![Paolo Valente](/assets/img/avatar_default.png)
On each deactivation or re-scheduling (after being served) of a bfq_queue, BFQ invokes the function __bfq_entity_update_weight_prio(), to perform pending updates of ioprio, weight and ioprio class for the bfq_queue. BFQ also invokes this function on I/O-request dispatches, to raise or lower weights more quickly when needed, thereby improving latency. However, the entity representing the bfq_queue may be on the active (sub)tree of a service tree when this happens, and, although with a very low probability, the bfq_queue may happen to also have a pending change of its ioprio class. If both conditions hold when __bfq_entity_update_weight_prio() is invoked, then the entity moves to a sort of hybrid state: the new service tree for the entity, as returned by bfq_entity_service_tree(), differs from service tree on which the entity still is. The functions that handle activations and deactivations of entities do not cope with such a hybrid state (and would need to become more complex to cope). This commit addresses this issue by just making __bfq_entity_update_weight_prio() not perform also a possible pending change of ioprio class, when invoked on an I/O-request dispatch for a bfq_queue. Such a change is thus postponed to when __bfq_entity_update_weight_prio() is invoked on deactivation or re-scheduling of the bfq_queue. Reported-by: Marco Piazza <mpiazza@gmail.com> Reported-by: Laurentiu Nicola <lnicola@dend.ro> Signed-off-by: Paolo Valente <paolo.valente@linaro.org> Tested-by: Marco Piazza <mpiazza@gmail.com> Signed-off-by: Jens Axboe <axboe@kernel.dk>
5074 lines
163 KiB
C
5074 lines
163 KiB
C
/*
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* Budget Fair Queueing (BFQ) I/O scheduler.
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*
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* Based on ideas and code from CFQ:
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* Copyright (C) 2003 Jens Axboe <axboe@kernel.dk>
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*
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* Copyright (C) 2008 Fabio Checconi <fabio@gandalf.sssup.it>
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* Paolo Valente <paolo.valente@unimore.it>
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*
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* Copyright (C) 2010 Paolo Valente <paolo.valente@unimore.it>
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* Arianna Avanzini <avanzini@google.com>
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*
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* Copyright (C) 2017 Paolo Valente <paolo.valente@linaro.org>
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*
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* This program is free software; you can redistribute it and/or
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* modify it under the terms of the GNU General Public License as
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* published by the Free Software Foundation; either version 2 of the
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* License, or (at your option) any later version.
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*
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* This program is distributed in the hope that it will be useful,
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* but WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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* General Public License for more details.
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*
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* BFQ is a proportional-share I/O scheduler, with some extra
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* low-latency capabilities. BFQ also supports full hierarchical
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* scheduling through cgroups. Next paragraphs provide an introduction
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* on BFQ inner workings. Details on BFQ benefits, usage and
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* limitations can be found in Documentation/block/bfq-iosched.txt.
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*
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* BFQ is a proportional-share storage-I/O scheduling algorithm based
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* on the slice-by-slice service scheme of CFQ. But BFQ assigns
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* budgets, measured in number of sectors, to processes instead of
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* time slices. The device is not granted to the in-service process
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* for a given time slice, but until it has exhausted its assigned
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* budget. This change from the time to the service domain enables BFQ
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* to distribute the device throughput among processes as desired,
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* without any distortion due to throughput fluctuations, or to device
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* internal queueing. BFQ uses an ad hoc internal scheduler, called
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* B-WF2Q+, to schedule processes according to their budgets. More
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* precisely, BFQ schedules queues associated with processes. Each
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* process/queue is assigned a user-configurable weight, and B-WF2Q+
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* guarantees that each queue receives a fraction of the throughput
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* proportional to its weight. Thanks to the accurate policy of
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* B-WF2Q+, BFQ can afford to assign high budgets to I/O-bound
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* processes issuing sequential requests (to boost the throughput),
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* and yet guarantee a low latency to interactive and soft real-time
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* applications.
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*
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* In particular, to provide these low-latency guarantees, BFQ
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* explicitly privileges the I/O of two classes of time-sensitive
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* applications: interactive and soft real-time. This feature enables
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* BFQ to provide applications in these classes with a very low
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* latency. Finally, BFQ also features additional heuristics for
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* preserving both a low latency and a high throughput on NCQ-capable,
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* rotational or flash-based devices, and to get the job done quickly
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* for applications consisting in many I/O-bound processes.
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*
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* NOTE: if the main or only goal, with a given device, is to achieve
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* the maximum-possible throughput at all times, then do switch off
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* all low-latency heuristics for that device, by setting low_latency
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* to 0.
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*
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* BFQ is described in [1], where also a reference to the initial, more
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* theoretical paper on BFQ can be found. The interested reader can find
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* in the latter paper full details on the main algorithm, as well as
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* formulas of the guarantees and formal proofs of all the properties.
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* With respect to the version of BFQ presented in these papers, this
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* implementation adds a few more heuristics, such as the one that
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* guarantees a low latency to soft real-time applications, and a
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* hierarchical extension based on H-WF2Q+.
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*
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* B-WF2Q+ is based on WF2Q+, which is described in [2], together with
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* H-WF2Q+, while the augmented tree used here to implement B-WF2Q+
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* with O(log N) complexity derives from the one introduced with EEVDF
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* in [3].
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*
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* [1] P. Valente, A. Avanzini, "Evolution of the BFQ Storage I/O
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* Scheduler", Proceedings of the First Workshop on Mobile System
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* Technologies (MST-2015), May 2015.
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* http://algogroup.unimore.it/people/paolo/disk_sched/mst-2015.pdf
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*
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* [2] Jon C.R. Bennett and H. Zhang, "Hierarchical Packet Fair Queueing
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* Algorithms", IEEE/ACM Transactions on Networking, 5(5):675-689,
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* Oct 1997.
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*
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* http://www.cs.cmu.edu/~hzhang/papers/TON-97-Oct.ps.gz
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*
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* [3] I. Stoica and H. Abdel-Wahab, "Earliest Eligible Virtual Deadline
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* First: A Flexible and Accurate Mechanism for Proportional Share
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* Resource Allocation", technical report.
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*
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* http://www.cs.berkeley.edu/~istoica/papers/eevdf-tr-95.pdf
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*/
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#include <linux/module.h>
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#include <linux/slab.h>
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#include <linux/blkdev.h>
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#include <linux/cgroup.h>
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#include <linux/elevator.h>
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#include <linux/ktime.h>
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#include <linux/rbtree.h>
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#include <linux/ioprio.h>
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#include <linux/sbitmap.h>
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#include <linux/delay.h>
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#include "blk.h"
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#include "blk-mq.h"
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#include "blk-mq-tag.h"
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#include "blk-mq-sched.h"
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#include "bfq-iosched.h"
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#define BFQ_BFQQ_FNS(name) \
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void bfq_mark_bfqq_##name(struct bfq_queue *bfqq) \
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{ \
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__set_bit(BFQQF_##name, &(bfqq)->flags); \
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} \
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void bfq_clear_bfqq_##name(struct bfq_queue *bfqq) \
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{ \
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__clear_bit(BFQQF_##name, &(bfqq)->flags); \
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} \
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int bfq_bfqq_##name(const struct bfq_queue *bfqq) \
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{ \
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return test_bit(BFQQF_##name, &(bfqq)->flags); \
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}
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BFQ_BFQQ_FNS(just_created);
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BFQ_BFQQ_FNS(busy);
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BFQ_BFQQ_FNS(wait_request);
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BFQ_BFQQ_FNS(non_blocking_wait_rq);
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BFQ_BFQQ_FNS(fifo_expire);
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BFQ_BFQQ_FNS(idle_window);
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BFQ_BFQQ_FNS(sync);
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BFQ_BFQQ_FNS(IO_bound);
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BFQ_BFQQ_FNS(in_large_burst);
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BFQ_BFQQ_FNS(coop);
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BFQ_BFQQ_FNS(split_coop);
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BFQ_BFQQ_FNS(softrt_update);
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#undef BFQ_BFQQ_FNS \
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/* Expiration time of sync (0) and async (1) requests, in ns. */
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static const u64 bfq_fifo_expire[2] = { NSEC_PER_SEC / 4, NSEC_PER_SEC / 8 };
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/* Maximum backwards seek (magic number lifted from CFQ), in KiB. */
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static const int bfq_back_max = 16 * 1024;
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/* Penalty of a backwards seek, in number of sectors. */
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static const int bfq_back_penalty = 2;
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/* Idling period duration, in ns. */
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static u64 bfq_slice_idle = NSEC_PER_SEC / 125;
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/* Minimum number of assigned budgets for which stats are safe to compute. */
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static const int bfq_stats_min_budgets = 194;
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/* Default maximum budget values, in sectors and number of requests. */
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static const int bfq_default_max_budget = 16 * 1024;
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/*
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* Async to sync throughput distribution is controlled as follows:
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* when an async request is served, the entity is charged the number
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* of sectors of the request, multiplied by the factor below
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*/
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static const int bfq_async_charge_factor = 10;
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/* Default timeout values, in jiffies, approximating CFQ defaults. */
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const int bfq_timeout = HZ / 8;
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static struct kmem_cache *bfq_pool;
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/* Below this threshold (in ns), we consider thinktime immediate. */
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#define BFQ_MIN_TT (2 * NSEC_PER_MSEC)
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/* hw_tag detection: parallel requests threshold and min samples needed. */
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#define BFQ_HW_QUEUE_THRESHOLD 4
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#define BFQ_HW_QUEUE_SAMPLES 32
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#define BFQQ_SEEK_THR (sector_t)(8 * 100)
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#define BFQQ_SECT_THR_NONROT (sector_t)(2 * 32)
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#define BFQQ_CLOSE_THR (sector_t)(8 * 1024)
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#define BFQQ_SEEKY(bfqq) (hweight32(bfqq->seek_history) > 32/8)
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/* Min number of samples required to perform peak-rate update */
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#define BFQ_RATE_MIN_SAMPLES 32
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/* Min observation time interval required to perform a peak-rate update (ns) */
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#define BFQ_RATE_MIN_INTERVAL (300*NSEC_PER_MSEC)
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/* Target observation time interval for a peak-rate update (ns) */
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#define BFQ_RATE_REF_INTERVAL NSEC_PER_SEC
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/* Shift used for peak rate fixed precision calculations. */
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#define BFQ_RATE_SHIFT 16
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/*
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* By default, BFQ computes the duration of the weight raising for
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* interactive applications automatically, using the following formula:
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* duration = (R / r) * T, where r is the peak rate of the device, and
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* R and T are two reference parameters.
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* In particular, R is the peak rate of the reference device (see below),
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* and T is a reference time: given the systems that are likely to be
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* installed on the reference device according to its speed class, T is
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* about the maximum time needed, under BFQ and while reading two files in
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* parallel, to load typical large applications on these systems.
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* In practice, the slower/faster the device at hand is, the more/less it
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* takes to load applications with respect to the reference device.
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* Accordingly, the longer/shorter BFQ grants weight raising to interactive
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* applications.
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*
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* BFQ uses four different reference pairs (R, T), depending on:
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* . whether the device is rotational or non-rotational;
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* . whether the device is slow, such as old or portable HDDs, as well as
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* SD cards, or fast, such as newer HDDs and SSDs.
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*
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* The device's speed class is dynamically (re)detected in
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* bfq_update_peak_rate() every time the estimated peak rate is updated.
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*
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* In the following definitions, R_slow[0]/R_fast[0] and
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* T_slow[0]/T_fast[0] are the reference values for a slow/fast
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* rotational device, whereas R_slow[1]/R_fast[1] and
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* T_slow[1]/T_fast[1] are the reference values for a slow/fast
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* non-rotational device. Finally, device_speed_thresh are the
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* thresholds used to switch between speed classes. The reference
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* rates are not the actual peak rates of the devices used as a
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* reference, but slightly lower values. The reason for using these
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* slightly lower values is that the peak-rate estimator tends to
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* yield slightly lower values than the actual peak rate (it can yield
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* the actual peak rate only if there is only one process doing I/O,
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* and the process does sequential I/O).
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*
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* Both the reference peak rates and the thresholds are measured in
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* sectors/usec, left-shifted by BFQ_RATE_SHIFT.
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*/
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static int R_slow[2] = {1000, 10700};
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static int R_fast[2] = {14000, 33000};
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/*
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* To improve readability, a conversion function is used to initialize the
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* following arrays, which entails that they can be initialized only in a
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* function.
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*/
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static int T_slow[2];
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static int T_fast[2];
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static int device_speed_thresh[2];
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#define RQ_BIC(rq) ((struct bfq_io_cq *) (rq)->elv.priv[0])
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#define RQ_BFQQ(rq) ((rq)->elv.priv[1])
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struct bfq_queue *bic_to_bfqq(struct bfq_io_cq *bic, bool is_sync)
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{
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return bic->bfqq[is_sync];
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}
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void bic_set_bfqq(struct bfq_io_cq *bic, struct bfq_queue *bfqq, bool is_sync)
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{
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bic->bfqq[is_sync] = bfqq;
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}
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struct bfq_data *bic_to_bfqd(struct bfq_io_cq *bic)
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{
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return bic->icq.q->elevator->elevator_data;
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}
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/**
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* icq_to_bic - convert iocontext queue structure to bfq_io_cq.
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* @icq: the iocontext queue.
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*/
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static struct bfq_io_cq *icq_to_bic(struct io_cq *icq)
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{
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/* bic->icq is the first member, %NULL will convert to %NULL */
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return container_of(icq, struct bfq_io_cq, icq);
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}
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/**
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* bfq_bic_lookup - search into @ioc a bic associated to @bfqd.
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* @bfqd: the lookup key.
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* @ioc: the io_context of the process doing I/O.
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* @q: the request queue.
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*/
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static struct bfq_io_cq *bfq_bic_lookup(struct bfq_data *bfqd,
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struct io_context *ioc,
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struct request_queue *q)
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{
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if (ioc) {
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unsigned long flags;
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struct bfq_io_cq *icq;
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spin_lock_irqsave(q->queue_lock, flags);
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icq = icq_to_bic(ioc_lookup_icq(ioc, q));
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spin_unlock_irqrestore(q->queue_lock, flags);
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return icq;
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}
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return NULL;
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}
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/*
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* Scheduler run of queue, if there are requests pending and no one in the
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* driver that will restart queueing.
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*/
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void bfq_schedule_dispatch(struct bfq_data *bfqd)
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{
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if (bfqd->queued != 0) {
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bfq_log(bfqd, "schedule dispatch");
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blk_mq_run_hw_queues(bfqd->queue, true);
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}
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}
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#define bfq_class_idle(bfqq) ((bfqq)->ioprio_class == IOPRIO_CLASS_IDLE)
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#define bfq_class_rt(bfqq) ((bfqq)->ioprio_class == IOPRIO_CLASS_RT)
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#define bfq_sample_valid(samples) ((samples) > 80)
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/*
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* Lifted from AS - choose which of rq1 and rq2 that is best served now.
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* We choose the request that is closesr to the head right now. Distance
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* behind the head is penalized and only allowed to a certain extent.
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*/
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static struct request *bfq_choose_req(struct bfq_data *bfqd,
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struct request *rq1,
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struct request *rq2,
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sector_t last)
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{
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sector_t s1, s2, d1 = 0, d2 = 0;
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unsigned long back_max;
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#define BFQ_RQ1_WRAP 0x01 /* request 1 wraps */
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#define BFQ_RQ2_WRAP 0x02 /* request 2 wraps */
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unsigned int wrap = 0; /* bit mask: requests behind the disk head? */
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if (!rq1 || rq1 == rq2)
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return rq2;
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if (!rq2)
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return rq1;
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if (rq_is_sync(rq1) && !rq_is_sync(rq2))
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return rq1;
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else if (rq_is_sync(rq2) && !rq_is_sync(rq1))
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return rq2;
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if ((rq1->cmd_flags & REQ_META) && !(rq2->cmd_flags & REQ_META))
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return rq1;
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else if ((rq2->cmd_flags & REQ_META) && !(rq1->cmd_flags & REQ_META))
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return rq2;
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s1 = blk_rq_pos(rq1);
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s2 = blk_rq_pos(rq2);
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/*
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* By definition, 1KiB is 2 sectors.
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*/
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back_max = bfqd->bfq_back_max * 2;
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/*
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* Strict one way elevator _except_ in the case where we allow
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* short backward seeks which are biased as twice the cost of a
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* similar forward seek.
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*/
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if (s1 >= last)
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d1 = s1 - last;
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else if (s1 + back_max >= last)
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d1 = (last - s1) * bfqd->bfq_back_penalty;
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else
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wrap |= BFQ_RQ1_WRAP;
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if (s2 >= last)
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d2 = s2 - last;
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else if (s2 + back_max >= last)
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d2 = (last - s2) * bfqd->bfq_back_penalty;
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else
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wrap |= BFQ_RQ2_WRAP;
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/* Found required data */
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/*
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* By doing switch() on the bit mask "wrap" we avoid having to
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* check two variables for all permutations: --> faster!
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*/
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switch (wrap) {
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case 0: /* common case for CFQ: rq1 and rq2 not wrapped */
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if (d1 < d2)
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return rq1;
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else if (d2 < d1)
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return rq2;
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if (s1 >= s2)
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return rq1;
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else
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return rq2;
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case BFQ_RQ2_WRAP:
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return rq1;
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case BFQ_RQ1_WRAP:
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return rq2;
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case BFQ_RQ1_WRAP|BFQ_RQ2_WRAP: /* both rqs wrapped */
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default:
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/*
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* Since both rqs are wrapped,
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* start with the one that's further behind head
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* (--> only *one* back seek required),
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* since back seek takes more time than forward.
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*/
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if (s1 <= s2)
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return rq1;
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else
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return rq2;
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}
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}
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static struct bfq_queue *
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bfq_rq_pos_tree_lookup(struct bfq_data *bfqd, struct rb_root *root,
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sector_t sector, struct rb_node **ret_parent,
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struct rb_node ***rb_link)
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{
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struct rb_node **p, *parent;
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struct bfq_queue *bfqq = NULL;
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parent = NULL;
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p = &root->rb_node;
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while (*p) {
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struct rb_node **n;
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parent = *p;
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bfqq = rb_entry(parent, struct bfq_queue, pos_node);
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/*
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* Sort strictly based on sector. Smallest to the left,
|
|
* largest to the right.
|
|
*/
|
|
if (sector > blk_rq_pos(bfqq->next_rq))
|
|
n = &(*p)->rb_right;
|
|
else if (sector < blk_rq_pos(bfqq->next_rq))
|
|
n = &(*p)->rb_left;
|
|
else
|
|
break;
|
|
p = n;
|
|
bfqq = NULL;
|
|
}
|
|
|
|
*ret_parent = parent;
|
|
if (rb_link)
|
|
*rb_link = p;
|
|
|
|
bfq_log(bfqd, "rq_pos_tree_lookup %llu: returning %d",
|
|
(unsigned long long)sector,
|
|
bfqq ? bfqq->pid : 0);
|
|
|
|
return bfqq;
|
|
}
|
|
|
|
void bfq_pos_tree_add_move(struct bfq_data *bfqd, struct bfq_queue *bfqq)
|
|
{
|
|
struct rb_node **p, *parent;
|
|
struct bfq_queue *__bfqq;
|
|
|
|
if (bfqq->pos_root) {
|
|
rb_erase(&bfqq->pos_node, bfqq->pos_root);
|
|
bfqq->pos_root = NULL;
|
|
}
|
|
|
|
if (bfq_class_idle(bfqq))
|
|
return;
|
|
if (!bfqq->next_rq)
|
|
return;
|
|
|
|
bfqq->pos_root = &bfq_bfqq_to_bfqg(bfqq)->rq_pos_tree;
|
|
__bfqq = bfq_rq_pos_tree_lookup(bfqd, bfqq->pos_root,
|
|
blk_rq_pos(bfqq->next_rq), &parent, &p);
|
|
if (!__bfqq) {
|
|
rb_link_node(&bfqq->pos_node, parent, p);
|
|
rb_insert_color(&bfqq->pos_node, bfqq->pos_root);
|
|
} else
|
|
bfqq->pos_root = NULL;
|
|
}
|
|
|
|
/*
|
|
* Tell whether there are active queues or groups with differentiated weights.
|
|
*/
|
|
static bool bfq_differentiated_weights(struct bfq_data *bfqd)
|
|
{
|
|
/*
|
|
* For weights to differ, at least one of the trees must contain
|
|
* at least two nodes.
|
|
*/
|
|
return (!RB_EMPTY_ROOT(&bfqd->queue_weights_tree) &&
|
|
(bfqd->queue_weights_tree.rb_node->rb_left ||
|
|
bfqd->queue_weights_tree.rb_node->rb_right)
|
|
#ifdef CONFIG_BFQ_GROUP_IOSCHED
|
|
) ||
|
|
(!RB_EMPTY_ROOT(&bfqd->group_weights_tree) &&
|
|
(bfqd->group_weights_tree.rb_node->rb_left ||
|
|
bfqd->group_weights_tree.rb_node->rb_right)
|
|
#endif
|
|
);
|
|
}
|
|
|
|
/*
|
|
* The following function returns true if every queue must receive the
|
|
* same share of the throughput (this condition is used when deciding
|
|
* whether idling may be disabled, see the comments in the function
|
|
* bfq_bfqq_may_idle()).
|
|
*
|
|
* Such a scenario occurs when:
|
|
* 1) all active queues have the same weight,
|
|
* 2) all active groups at the same level in the groups tree have the same
|
|
* weight,
|
|
* 3) all active groups at the same level in the groups tree have the same
|
|
* number of children.
|
|
*
|
|
* Unfortunately, keeping the necessary state for evaluating exactly the
|
|
* above symmetry conditions would be quite complex and time-consuming.
|
|
* Therefore this function evaluates, instead, the following stronger
|
|
* sub-conditions, for which it is much easier to maintain the needed
|
|
* state:
|
|
* 1) all active queues have the same weight,
|
|
* 2) all active groups have the same weight,
|
|
* 3) all active groups have at most one active child each.
|
|
* In particular, the last two conditions are always true if hierarchical
|
|
* support and the cgroups interface are not enabled, thus no state needs
|
|
* to be maintained in this case.
|
|
*/
|
|
static bool bfq_symmetric_scenario(struct bfq_data *bfqd)
|
|
{
|
|
return !bfq_differentiated_weights(bfqd);
|
|
}
|
|
|
|
/*
|
|
* If the weight-counter tree passed as input contains no counter for
|
|
* the weight of the input entity, then add that counter; otherwise just
|
|
* increment the existing counter.
|
|
*
|
|
* Note that weight-counter trees contain few nodes in mostly symmetric
|
|
* scenarios. For example, if all queues have the same weight, then the
|
|
* weight-counter tree for the queues may contain at most one node.
|
|
* This holds even if low_latency is on, because weight-raised queues
|
|
* are not inserted in the tree.
|
|
* In most scenarios, the rate at which nodes are created/destroyed
|
|
* should be low too.
|
|
*/
|
|
void bfq_weights_tree_add(struct bfq_data *bfqd, struct bfq_entity *entity,
|
|
struct rb_root *root)
|
|
{
|
|
struct rb_node **new = &(root->rb_node), *parent = NULL;
|
|
|
|
/*
|
|
* Do not insert if the entity is already associated with a
|
|
* counter, which happens if:
|
|
* 1) the entity is associated with a queue,
|
|
* 2) a request arrival has caused the queue to become both
|
|
* non-weight-raised, and hence change its weight, and
|
|
* backlogged; in this respect, each of the two events
|
|
* causes an invocation of this function,
|
|
* 3) this is the invocation of this function caused by the
|
|
* second event. This second invocation is actually useless,
|
|
* and we handle this fact by exiting immediately. More
|
|
* efficient or clearer solutions might possibly be adopted.
|
|
*/
|
|
if (entity->weight_counter)
|
|
return;
|
|
|
|
while (*new) {
|
|
struct bfq_weight_counter *__counter = container_of(*new,
|
|
struct bfq_weight_counter,
|
|
weights_node);
|
|
parent = *new;
|
|
|
|
if (entity->weight == __counter->weight) {
|
|
entity->weight_counter = __counter;
|
|
goto inc_counter;
|
|
}
|
|
if (entity->weight < __counter->weight)
|
|
new = &((*new)->rb_left);
|
|
else
|
|
new = &((*new)->rb_right);
|
|
}
|
|
|
|
entity->weight_counter = kzalloc(sizeof(struct bfq_weight_counter),
|
|
GFP_ATOMIC);
|
|
|
|
/*
|
|
* In the unlucky event of an allocation failure, we just
|
|
* exit. This will cause the weight of entity to not be
|
|
* considered in bfq_differentiated_weights, which, in its
|
|
* turn, causes the scenario to be deemed wrongly symmetric in
|
|
* case entity's weight would have been the only weight making
|
|
* the scenario asymmetric. On the bright side, no unbalance
|
|
* will however occur when entity becomes inactive again (the
|
|
* invocation of this function is triggered by an activation
|
|
* of entity). In fact, bfq_weights_tree_remove does nothing
|
|
* if !entity->weight_counter.
|
|
*/
|
|
if (unlikely(!entity->weight_counter))
|
|
return;
|
|
|
|
entity->weight_counter->weight = entity->weight;
|
|
rb_link_node(&entity->weight_counter->weights_node, parent, new);
|
|
rb_insert_color(&entity->weight_counter->weights_node, root);
|
|
|
|
inc_counter:
|
|
entity->weight_counter->num_active++;
|
|
}
|
|
|
|
/*
|
|
* Decrement the weight counter associated with the entity, and, if the
|
|
* counter reaches 0, remove the counter from the tree.
|
|
* See the comments to the function bfq_weights_tree_add() for considerations
|
|
* about overhead.
|
|
*/
|
|
void bfq_weights_tree_remove(struct bfq_data *bfqd, struct bfq_entity *entity,
|
|
struct rb_root *root)
|
|
{
|
|
if (!entity->weight_counter)
|
|
return;
|
|
|
|
entity->weight_counter->num_active--;
|
|
if (entity->weight_counter->num_active > 0)
|
|
goto reset_entity_pointer;
|
|
|
|
rb_erase(&entity->weight_counter->weights_node, root);
|
|
kfree(entity->weight_counter);
|
|
|
|
reset_entity_pointer:
|
|
entity->weight_counter = NULL;
|
|
}
|
|
|
|
/*
|
|
* Return expired entry, or NULL to just start from scratch in rbtree.
|
|
*/
|
|
static struct request *bfq_check_fifo(struct bfq_queue *bfqq,
|
|
struct request *last)
|
|
{
|
|
struct request *rq;
|
|
|
|
if (bfq_bfqq_fifo_expire(bfqq))
|
|
return NULL;
|
|
|
|
bfq_mark_bfqq_fifo_expire(bfqq);
|
|
|
|
rq = rq_entry_fifo(bfqq->fifo.next);
|
|
|
|
if (rq == last || ktime_get_ns() < rq->fifo_time)
|
|
return NULL;
|
|
|
|
bfq_log_bfqq(bfqq->bfqd, bfqq, "check_fifo: returned %p", rq);
|
|
return rq;
|
|
}
|
|
|
|
static struct request *bfq_find_next_rq(struct bfq_data *bfqd,
|
|
struct bfq_queue *bfqq,
|
|
struct request *last)
|
|
{
|
|
struct rb_node *rbnext = rb_next(&last->rb_node);
|
|
struct rb_node *rbprev = rb_prev(&last->rb_node);
|
|
struct request *next, *prev = NULL;
|
|
|
|
/* Follow expired path, else get first next available. */
|
|
next = bfq_check_fifo(bfqq, last);
|
|
if (next)
|
|
return next;
|
|
|
|
if (rbprev)
|
|
prev = rb_entry_rq(rbprev);
|
|
|
|
if (rbnext)
|
|
next = rb_entry_rq(rbnext);
|
|
else {
|
|
rbnext = rb_first(&bfqq->sort_list);
|
|
if (rbnext && rbnext != &last->rb_node)
|
|
next = rb_entry_rq(rbnext);
|
|
}
|
|
|
|
return bfq_choose_req(bfqd, next, prev, blk_rq_pos(last));
|
|
}
|
|
|
|
/* see the definition of bfq_async_charge_factor for details */
|
|
static unsigned long bfq_serv_to_charge(struct request *rq,
|
|
struct bfq_queue *bfqq)
|
|
{
|
|
if (bfq_bfqq_sync(bfqq) || bfqq->wr_coeff > 1)
|
|
return blk_rq_sectors(rq);
|
|
|
|
/*
|
|
* If there are no weight-raised queues, then amplify service
|
|
* by just the async charge factor; otherwise amplify service
|
|
* by twice the async charge factor, to further reduce latency
|
|
* for weight-raised queues.
|
|
*/
|
|
if (bfqq->bfqd->wr_busy_queues == 0)
|
|
return blk_rq_sectors(rq) * bfq_async_charge_factor;
|
|
|
|
return blk_rq_sectors(rq) * 2 * bfq_async_charge_factor;
|
|
}
|
|
|
|
/**
|
|
* bfq_updated_next_req - update the queue after a new next_rq selection.
|
|
* @bfqd: the device data the queue belongs to.
|
|
* @bfqq: the queue to update.
|
|
*
|
|
* If the first request of a queue changes we make sure that the queue
|
|
* has enough budget to serve at least its first request (if the
|
|
* request has grown). We do this because if the queue has not enough
|
|
* budget for its first request, it has to go through two dispatch
|
|
* rounds to actually get it dispatched.
|
|
*/
|
|
static void bfq_updated_next_req(struct bfq_data *bfqd,
|
|
struct bfq_queue *bfqq)
|
|
{
|
|
struct bfq_entity *entity = &bfqq->entity;
|
|
struct request *next_rq = bfqq->next_rq;
|
|
unsigned long new_budget;
|
|
|
|
if (!next_rq)
|
|
return;
|
|
|
|
if (bfqq == bfqd->in_service_queue)
|
|
/*
|
|
* In order not to break guarantees, budgets cannot be
|
|
* changed after an entity has been selected.
|
|
*/
|
|
return;
|
|
|
|
new_budget = max_t(unsigned long, bfqq->max_budget,
|
|
bfq_serv_to_charge(next_rq, bfqq));
|
|
if (entity->budget != new_budget) {
|
|
entity->budget = new_budget;
|
|
bfq_log_bfqq(bfqd, bfqq, "updated next rq: new budget %lu",
|
|
new_budget);
|
|
bfq_requeue_bfqq(bfqd, bfqq);
|
|
}
|
|
}
|
|
|
|
static void
|
|
bfq_bfqq_resume_state(struct bfq_queue *bfqq, struct bfq_data *bfqd,
|
|
struct bfq_io_cq *bic, bool bfq_already_existing)
|
|
{
|
|
unsigned int old_wr_coeff = bfqq->wr_coeff;
|
|
bool busy = bfq_already_existing && bfq_bfqq_busy(bfqq);
|
|
|
|
if (bic->saved_idle_window)
|
|
bfq_mark_bfqq_idle_window(bfqq);
|
|
else
|
|
bfq_clear_bfqq_idle_window(bfqq);
|
|
|
|
if (bic->saved_IO_bound)
|
|
bfq_mark_bfqq_IO_bound(bfqq);
|
|
else
|
|
bfq_clear_bfqq_IO_bound(bfqq);
|
|
|
|
bfqq->ttime = bic->saved_ttime;
|
|
bfqq->wr_coeff = bic->saved_wr_coeff;
|
|
bfqq->wr_start_at_switch_to_srt = bic->saved_wr_start_at_switch_to_srt;
|
|
bfqq->last_wr_start_finish = bic->saved_last_wr_start_finish;
|
|
bfqq->wr_cur_max_time = bic->saved_wr_cur_max_time;
|
|
|
|
if (bfqq->wr_coeff > 1 && (bfq_bfqq_in_large_burst(bfqq) ||
|
|
time_is_before_jiffies(bfqq->last_wr_start_finish +
|
|
bfqq->wr_cur_max_time))) {
|
|
bfq_log_bfqq(bfqq->bfqd, bfqq,
|
|
"resume state: switching off wr");
|
|
|
|
bfqq->wr_coeff = 1;
|
|
}
|
|
|
|
/* make sure weight will be updated, however we got here */
|
|
bfqq->entity.prio_changed = 1;
|
|
|
|
if (likely(!busy))
|
|
return;
|
|
|
|
if (old_wr_coeff == 1 && bfqq->wr_coeff > 1)
|
|
bfqd->wr_busy_queues++;
|
|
else if (old_wr_coeff > 1 && bfqq->wr_coeff == 1)
|
|
bfqd->wr_busy_queues--;
|
|
}
|
|
|
|
static int bfqq_process_refs(struct bfq_queue *bfqq)
|
|
{
|
|
return bfqq->ref - bfqq->allocated - bfqq->entity.on_st;
|
|
}
|
|
|
|
/* Empty burst list and add just bfqq (see comments on bfq_handle_burst) */
|
|
static void bfq_reset_burst_list(struct bfq_data *bfqd, struct bfq_queue *bfqq)
|
|
{
|
|
struct bfq_queue *item;
|
|
struct hlist_node *n;
|
|
|
|
hlist_for_each_entry_safe(item, n, &bfqd->burst_list, burst_list_node)
|
|
hlist_del_init(&item->burst_list_node);
|
|
hlist_add_head(&bfqq->burst_list_node, &bfqd->burst_list);
|
|
bfqd->burst_size = 1;
|
|
bfqd->burst_parent_entity = bfqq->entity.parent;
|
|
}
|
|
|
|
/* Add bfqq to the list of queues in current burst (see bfq_handle_burst) */
|
|
static void bfq_add_to_burst(struct bfq_data *bfqd, struct bfq_queue *bfqq)
|
|
{
|
|
/* Increment burst size to take into account also bfqq */
|
|
bfqd->burst_size++;
|
|
|
|
if (bfqd->burst_size == bfqd->bfq_large_burst_thresh) {
|
|
struct bfq_queue *pos, *bfqq_item;
|
|
struct hlist_node *n;
|
|
|
|
/*
|
|
* Enough queues have been activated shortly after each
|
|
* other to consider this burst as large.
|
|
*/
|
|
bfqd->large_burst = true;
|
|
|
|
/*
|
|
* We can now mark all queues in the burst list as
|
|
* belonging to a large burst.
|
|
*/
|
|
hlist_for_each_entry(bfqq_item, &bfqd->burst_list,
|
|
burst_list_node)
|
|
bfq_mark_bfqq_in_large_burst(bfqq_item);
|
|
bfq_mark_bfqq_in_large_burst(bfqq);
|
|
|
|
/*
|
|
* From now on, and until the current burst finishes, any
|
|
* new queue being activated shortly after the last queue
|
|
* was inserted in the burst can be immediately marked as
|
|
* belonging to a large burst. So the burst list is not
|
|
* needed any more. Remove it.
|
|
*/
|
|
hlist_for_each_entry_safe(pos, n, &bfqd->burst_list,
|
|
burst_list_node)
|
|
hlist_del_init(&pos->burst_list_node);
|
|
} else /*
|
|
* Burst not yet large: add bfqq to the burst list. Do
|
|
* not increment the ref counter for bfqq, because bfqq
|
|
* is removed from the burst list before freeing bfqq
|
|
* in put_queue.
|
|
*/
|
|
hlist_add_head(&bfqq->burst_list_node, &bfqd->burst_list);
|
|
}
|
|
|
|
/*
|
|
* If many queues belonging to the same group happen to be created
|
|
* shortly after each other, then the processes associated with these
|
|
* queues have typically a common goal. In particular, bursts of queue
|
|
* creations are usually caused by services or applications that spawn
|
|
* many parallel threads/processes. Examples are systemd during boot,
|
|
* or git grep. To help these processes get their job done as soon as
|
|
* possible, it is usually better to not grant either weight-raising
|
|
* or device idling to their queues.
|
|
*
|
|
* In this comment we describe, firstly, the reasons why this fact
|
|
* holds, and, secondly, the next function, which implements the main
|
|
* steps needed to properly mark these queues so that they can then be
|
|
* treated in a different way.
|
|
*
|
|
* The above services or applications benefit mostly from a high
|
|
* throughput: the quicker the requests of the activated queues are
|
|
* cumulatively served, the sooner the target job of these queues gets
|
|
* completed. As a consequence, weight-raising any of these queues,
|
|
* which also implies idling the device for it, is almost always
|
|
* counterproductive. In most cases it just lowers throughput.
|
|
*
|
|
* On the other hand, a burst of queue creations may be caused also by
|
|
* the start of an application that does not consist of a lot of
|
|
* parallel I/O-bound threads. In fact, with a complex application,
|
|
* several short processes may need to be executed to start-up the
|
|
* application. In this respect, to start an application as quickly as
|
|
* possible, the best thing to do is in any case to privilege the I/O
|
|
* related to the application with respect to all other
|
|
* I/O. Therefore, the best strategy to start as quickly as possible
|
|
* an application that causes a burst of queue creations is to
|
|
* weight-raise all the queues created during the burst. This is the
|
|
* exact opposite of the best strategy for the other type of bursts.
|
|
*
|
|
* In the end, to take the best action for each of the two cases, the
|
|
* two types of bursts need to be distinguished. Fortunately, this
|
|
* seems relatively easy, by looking at the sizes of the bursts. In
|
|
* particular, we found a threshold such that only bursts with a
|
|
* larger size than that threshold are apparently caused by
|
|
* services or commands such as systemd or git grep. For brevity,
|
|
* hereafter we call just 'large' these bursts. BFQ *does not*
|
|
* weight-raise queues whose creation occurs in a large burst. In
|
|
* addition, for each of these queues BFQ performs or does not perform
|
|
* idling depending on which choice boosts the throughput more. The
|
|
* exact choice depends on the device and request pattern at
|
|
* hand.
|
|
*
|
|
* Unfortunately, false positives may occur while an interactive task
|
|
* is starting (e.g., an application is being started). The
|
|
* consequence is that the queues associated with the task do not
|
|
* enjoy weight raising as expected. Fortunately these false positives
|
|
* are very rare. They typically occur if some service happens to
|
|
* start doing I/O exactly when the interactive task starts.
|
|
*
|
|
* Turning back to the next function, it implements all the steps
|
|
* needed to detect the occurrence of a large burst and to properly
|
|
* mark all the queues belonging to it (so that they can then be
|
|
* treated in a different way). This goal is achieved by maintaining a
|
|
* "burst list" that holds, temporarily, the queues that belong to the
|
|
* burst in progress. The list is then used to mark these queues as
|
|
* belonging to a large burst if the burst does become large. The main
|
|
* steps are the following.
|
|
*
|
|
* . when the very first queue is created, the queue is inserted into the
|
|
* list (as it could be the first queue in a possible burst)
|
|
*
|
|
* . if the current burst has not yet become large, and a queue Q that does
|
|
* not yet belong to the burst is activated shortly after the last time
|
|
* at which a new queue entered the burst list, then the function appends
|
|
* Q to the burst list
|
|
*
|
|
* . if, as a consequence of the previous step, the burst size reaches
|
|
* the large-burst threshold, then
|
|
*
|
|
* . all the queues in the burst list are marked as belonging to a
|
|
* large burst
|
|
*
|
|
* . the burst list is deleted; in fact, the burst list already served
|
|
* its purpose (keeping temporarily track of the queues in a burst,
|
|
* so as to be able to mark them as belonging to a large burst in the
|
|
* previous sub-step), and now is not needed any more
|
|
*
|
|
* . the device enters a large-burst mode
|
|
*
|
|
* . if a queue Q that does not belong to the burst is created while
|
|
* the device is in large-burst mode and shortly after the last time
|
|
* at which a queue either entered the burst list or was marked as
|
|
* belonging to the current large burst, then Q is immediately marked
|
|
* as belonging to a large burst.
|
|
*
|
|
* . if a queue Q that does not belong to the burst is created a while
|
|
* later, i.e., not shortly after, than the last time at which a queue
|
|
* either entered the burst list or was marked as belonging to the
|
|
* current large burst, then the current burst is deemed as finished and:
|
|
*
|
|
* . the large-burst mode is reset if set
|
|
*
|
|
* . the burst list is emptied
|
|
*
|
|
* . Q is inserted in the burst list, as Q may be the first queue
|
|
* in a possible new burst (then the burst list contains just Q
|
|
* after this step).
|
|
*/
|
|
static void bfq_handle_burst(struct bfq_data *bfqd, struct bfq_queue *bfqq)
|
|
{
|
|
/*
|
|
* If bfqq is already in the burst list or is part of a large
|
|
* burst, or finally has just been split, then there is
|
|
* nothing else to do.
|
|
*/
|
|
if (!hlist_unhashed(&bfqq->burst_list_node) ||
|
|
bfq_bfqq_in_large_burst(bfqq) ||
|
|
time_is_after_eq_jiffies(bfqq->split_time +
|
|
msecs_to_jiffies(10)))
|
|
return;
|
|
|
|
/*
|
|
* If bfqq's creation happens late enough, or bfqq belongs to
|
|
* a different group than the burst group, then the current
|
|
* burst is finished, and related data structures must be
|
|
* reset.
|
|
*
|
|
* In this respect, consider the special case where bfqq is
|
|
* the very first queue created after BFQ is selected for this
|
|
* device. In this case, last_ins_in_burst and
|
|
* burst_parent_entity are not yet significant when we get
|
|
* here. But it is easy to verify that, whether or not the
|
|
* following condition is true, bfqq will end up being
|
|
* inserted into the burst list. In particular the list will
|
|
* happen to contain only bfqq. And this is exactly what has
|
|
* to happen, as bfqq may be the first queue of the first
|
|
* burst.
|
|
*/
|
|
if (time_is_before_jiffies(bfqd->last_ins_in_burst +
|
|
bfqd->bfq_burst_interval) ||
|
|
bfqq->entity.parent != bfqd->burst_parent_entity) {
|
|
bfqd->large_burst = false;
|
|
bfq_reset_burst_list(bfqd, bfqq);
|
|
goto end;
|
|
}
|
|
|
|
/*
|
|
* If we get here, then bfqq is being activated shortly after the
|
|
* last queue. So, if the current burst is also large, we can mark
|
|
* bfqq as belonging to this large burst immediately.
|
|
*/
|
|
if (bfqd->large_burst) {
|
|
bfq_mark_bfqq_in_large_burst(bfqq);
|
|
goto end;
|
|
}
|
|
|
|
/*
|
|
* If we get here, then a large-burst state has not yet been
|
|
* reached, but bfqq is being activated shortly after the last
|
|
* queue. Then we add bfqq to the burst.
|
|
*/
|
|
bfq_add_to_burst(bfqd, bfqq);
|
|
end:
|
|
/*
|
|
* At this point, bfqq either has been added to the current
|
|
* burst or has caused the current burst to terminate and a
|
|
* possible new burst to start. In particular, in the second
|
|
* case, bfqq has become the first queue in the possible new
|
|
* burst. In both cases last_ins_in_burst needs to be moved
|
|
* forward.
|
|
*/
|
|
bfqd->last_ins_in_burst = jiffies;
|
|
}
|
|
|
|
static int bfq_bfqq_budget_left(struct bfq_queue *bfqq)
|
|
{
|
|
struct bfq_entity *entity = &bfqq->entity;
|
|
|
|
return entity->budget - entity->service;
|
|
}
|
|
|
|
/*
|
|
* If enough samples have been computed, return the current max budget
|
|
* stored in bfqd, which is dynamically updated according to the
|
|
* estimated disk peak rate; otherwise return the default max budget
|
|
*/
|
|
static int bfq_max_budget(struct bfq_data *bfqd)
|
|
{
|
|
if (bfqd->budgets_assigned < bfq_stats_min_budgets)
|
|
return bfq_default_max_budget;
|
|
else
|
|
return bfqd->bfq_max_budget;
|
|
}
|
|
|
|
/*
|
|
* Return min budget, which is a fraction of the current or default
|
|
* max budget (trying with 1/32)
|
|
*/
|
|
static int bfq_min_budget(struct bfq_data *bfqd)
|
|
{
|
|
if (bfqd->budgets_assigned < bfq_stats_min_budgets)
|
|
return bfq_default_max_budget / 32;
|
|
else
|
|
return bfqd->bfq_max_budget / 32;
|
|
}
|
|
|
|
/*
|
|
* The next function, invoked after the input queue bfqq switches from
|
|
* idle to busy, updates the budget of bfqq. The function also tells
|
|
* whether the in-service queue should be expired, by returning
|
|
* true. The purpose of expiring the in-service queue is to give bfqq
|
|
* the chance to possibly preempt the in-service queue, and the reason
|
|
* for preempting the in-service queue is to achieve one of the two
|
|
* goals below.
|
|
*
|
|
* 1. Guarantee to bfqq its reserved bandwidth even if bfqq has
|
|
* expired because it has remained idle. In particular, bfqq may have
|
|
* expired for one of the following two reasons:
|
|
*
|
|
* - BFQQE_NO_MORE_REQUESTS bfqq did not enjoy any device idling
|
|
* and did not make it to issue a new request before its last
|
|
* request was served;
|
|
*
|
|
* - BFQQE_TOO_IDLE bfqq did enjoy device idling, but did not issue
|
|
* a new request before the expiration of the idling-time.
|
|
*
|
|
* Even if bfqq has expired for one of the above reasons, the process
|
|
* associated with the queue may be however issuing requests greedily,
|
|
* and thus be sensitive to the bandwidth it receives (bfqq may have
|
|
* remained idle for other reasons: CPU high load, bfqq not enjoying
|
|
* idling, I/O throttling somewhere in the path from the process to
|
|
* the I/O scheduler, ...). But if, after every expiration for one of
|
|
* the above two reasons, bfqq has to wait for the service of at least
|
|
* one full budget of another queue before being served again, then
|
|
* bfqq is likely to get a much lower bandwidth or resource time than
|
|
* its reserved ones. To address this issue, two countermeasures need
|
|
* to be taken.
|
|
*
|
|
* First, the budget and the timestamps of bfqq need to be updated in
|
|
* a special way on bfqq reactivation: they need to be updated as if
|
|
* bfqq did not remain idle and did not expire. In fact, if they are
|
|
* computed as if bfqq expired and remained idle until reactivation,
|
|
* then the process associated with bfqq is treated as if, instead of
|
|
* being greedy, it stopped issuing requests when bfqq remained idle,
|
|
* and restarts issuing requests only on this reactivation. In other
|
|
* words, the scheduler does not help the process recover the "service
|
|
* hole" between bfqq expiration and reactivation. As a consequence,
|
|
* the process receives a lower bandwidth than its reserved one. In
|
|
* contrast, to recover this hole, the budget must be updated as if
|
|
* bfqq was not expired at all before this reactivation, i.e., it must
|
|
* be set to the value of the remaining budget when bfqq was
|
|
* expired. Along the same line, timestamps need to be assigned the
|
|
* value they had the last time bfqq was selected for service, i.e.,
|
|
* before last expiration. Thus timestamps need to be back-shifted
|
|
* with respect to their normal computation (see [1] for more details
|
|
* on this tricky aspect).
|
|
*
|
|
* Secondly, to allow the process to recover the hole, the in-service
|
|
* queue must be expired too, to give bfqq the chance to preempt it
|
|
* immediately. In fact, if bfqq has to wait for a full budget of the
|
|
* in-service queue to be completed, then it may become impossible to
|
|
* let the process recover the hole, even if the back-shifted
|
|
* timestamps of bfqq are lower than those of the in-service queue. If
|
|
* this happens for most or all of the holes, then the process may not
|
|
* receive its reserved bandwidth. In this respect, it is worth noting
|
|
* that, being the service of outstanding requests unpreemptible, a
|
|
* little fraction of the holes may however be unrecoverable, thereby
|
|
* causing a little loss of bandwidth.
|
|
*
|
|
* The last important point is detecting whether bfqq does need this
|
|
* bandwidth recovery. In this respect, the next function deems the
|
|
* process associated with bfqq greedy, and thus allows it to recover
|
|
* the hole, if: 1) the process is waiting for the arrival of a new
|
|
* request (which implies that bfqq expired for one of the above two
|
|
* reasons), and 2) such a request has arrived soon. The first
|
|
* condition is controlled through the flag non_blocking_wait_rq,
|
|
* while the second through the flag arrived_in_time. If both
|
|
* conditions hold, then the function computes the budget in the
|
|
* above-described special way, and signals that the in-service queue
|
|
* should be expired. Timestamp back-shifting is done later in
|
|
* __bfq_activate_entity.
|
|
*
|
|
* 2. Reduce latency. Even if timestamps are not backshifted to let
|
|
* the process associated with bfqq recover a service hole, bfqq may
|
|
* however happen to have, after being (re)activated, a lower finish
|
|
* timestamp than the in-service queue. That is, the next budget of
|
|
* bfqq may have to be completed before the one of the in-service
|
|
* queue. If this is the case, then preempting the in-service queue
|
|
* allows this goal to be achieved, apart from the unpreemptible,
|
|
* outstanding requests mentioned above.
|
|
*
|
|
* Unfortunately, regardless of which of the above two goals one wants
|
|
* to achieve, service trees need first to be updated to know whether
|
|
* the in-service queue must be preempted. To have service trees
|
|
* correctly updated, the in-service queue must be expired and
|
|
* rescheduled, and bfqq must be scheduled too. This is one of the
|
|
* most costly operations (in future versions, the scheduling
|
|
* mechanism may be re-designed in such a way to make it possible to
|
|
* know whether preemption is needed without needing to update service
|
|
* trees). In addition, queue preemptions almost always cause random
|
|
* I/O, and thus loss of throughput. Because of these facts, the next
|
|
* function adopts the following simple scheme to avoid both costly
|
|
* operations and too frequent preemptions: it requests the expiration
|
|
* of the in-service queue (unconditionally) only for queues that need
|
|
* to recover a hole, or that either are weight-raised or deserve to
|
|
* be weight-raised.
|
|
*/
|
|
static bool bfq_bfqq_update_budg_for_activation(struct bfq_data *bfqd,
|
|
struct bfq_queue *bfqq,
|
|
bool arrived_in_time,
|
|
bool wr_or_deserves_wr)
|
|
{
|
|
struct bfq_entity *entity = &bfqq->entity;
|
|
|
|
if (bfq_bfqq_non_blocking_wait_rq(bfqq) && arrived_in_time) {
|
|
/*
|
|
* We do not clear the flag non_blocking_wait_rq here, as
|
|
* the latter is used in bfq_activate_bfqq to signal
|
|
* that timestamps need to be back-shifted (and is
|
|
* cleared right after).
|
|
*/
|
|
|
|
/*
|
|
* In next assignment we rely on that either
|
|
* entity->service or entity->budget are not updated
|
|
* on expiration if bfqq is empty (see
|
|
* __bfq_bfqq_recalc_budget). Thus both quantities
|
|
* remain unchanged after such an expiration, and the
|
|
* following statement therefore assigns to
|
|
* entity->budget the remaining budget on such an
|
|
* expiration. For clarity, entity->service is not
|
|
* updated on expiration in any case, and, in normal
|
|
* operation, is reset only when bfqq is selected for
|
|
* service (see bfq_get_next_queue).
|
|
*/
|
|
entity->budget = min_t(unsigned long,
|
|
bfq_bfqq_budget_left(bfqq),
|
|
bfqq->max_budget);
|
|
|
|
return true;
|
|
}
|
|
|
|
entity->budget = max_t(unsigned long, bfqq->max_budget,
|
|
bfq_serv_to_charge(bfqq->next_rq, bfqq));
|
|
bfq_clear_bfqq_non_blocking_wait_rq(bfqq);
|
|
return wr_or_deserves_wr;
|
|
}
|
|
|
|
static unsigned int bfq_wr_duration(struct bfq_data *bfqd)
|
|
{
|
|
u64 dur;
|
|
|
|
if (bfqd->bfq_wr_max_time > 0)
|
|
return bfqd->bfq_wr_max_time;
|
|
|
|
dur = bfqd->RT_prod;
|
|
do_div(dur, bfqd->peak_rate);
|
|
|
|
/*
|
|
* Limit duration between 3 and 13 seconds. Tests show that
|
|
* higher values than 13 seconds often yield the opposite of
|
|
* the desired result, i.e., worsen responsiveness by letting
|
|
* non-interactive and non-soft-real-time applications
|
|
* preserve weight raising for a too long time interval.
|
|
*
|
|
* On the other end, lower values than 3 seconds make it
|
|
* difficult for most interactive tasks to complete their jobs
|
|
* before weight-raising finishes.
|
|
*/
|
|
if (dur > msecs_to_jiffies(13000))
|
|
dur = msecs_to_jiffies(13000);
|
|
else if (dur < msecs_to_jiffies(3000))
|
|
dur = msecs_to_jiffies(3000);
|
|
|
|
return dur;
|
|
}
|
|
|
|
static void bfq_update_bfqq_wr_on_rq_arrival(struct bfq_data *bfqd,
|
|
struct bfq_queue *bfqq,
|
|
unsigned int old_wr_coeff,
|
|
bool wr_or_deserves_wr,
|
|
bool interactive,
|
|
bool in_burst,
|
|
bool soft_rt)
|
|
{
|
|
if (old_wr_coeff == 1 && wr_or_deserves_wr) {
|
|
/* start a weight-raising period */
|
|
if (interactive) {
|
|
bfqq->wr_coeff = bfqd->bfq_wr_coeff;
|
|
bfqq->wr_cur_max_time = bfq_wr_duration(bfqd);
|
|
} else {
|
|
bfqq->wr_start_at_switch_to_srt = jiffies;
|
|
bfqq->wr_coeff = bfqd->bfq_wr_coeff *
|
|
BFQ_SOFTRT_WEIGHT_FACTOR;
|
|
bfqq->wr_cur_max_time =
|
|
bfqd->bfq_wr_rt_max_time;
|
|
}
|
|
|
|
/*
|
|
* If needed, further reduce budget to make sure it is
|
|
* close to bfqq's backlog, so as to reduce the
|
|
* scheduling-error component due to a too large
|
|
* budget. Do not care about throughput consequences,
|
|
* but only about latency. Finally, do not assign a
|
|
* too small budget either, to avoid increasing
|
|
* latency by causing too frequent expirations.
|
|
*/
|
|
bfqq->entity.budget = min_t(unsigned long,
|
|
bfqq->entity.budget,
|
|
2 * bfq_min_budget(bfqd));
|
|
} else if (old_wr_coeff > 1) {
|
|
if (interactive) { /* update wr coeff and duration */
|
|
bfqq->wr_coeff = bfqd->bfq_wr_coeff;
|
|
bfqq->wr_cur_max_time = bfq_wr_duration(bfqd);
|
|
} else if (in_burst)
|
|
bfqq->wr_coeff = 1;
|
|
else if (soft_rt) {
|
|
/*
|
|
* The application is now or still meeting the
|
|
* requirements for being deemed soft rt. We
|
|
* can then correctly and safely (re)charge
|
|
* the weight-raising duration for the
|
|
* application with the weight-raising
|
|
* duration for soft rt applications.
|
|
*
|
|
* In particular, doing this recharge now, i.e.,
|
|
* before the weight-raising period for the
|
|
* application finishes, reduces the probability
|
|
* of the following negative scenario:
|
|
* 1) the weight of a soft rt application is
|
|
* raised at startup (as for any newly
|
|
* created application),
|
|
* 2) since the application is not interactive,
|
|
* at a certain time weight-raising is
|
|
* stopped for the application,
|
|
* 3) at that time the application happens to
|
|
* still have pending requests, and hence
|
|
* is destined to not have a chance to be
|
|
* deemed soft rt before these requests are
|
|
* completed (see the comments to the
|
|
* function bfq_bfqq_softrt_next_start()
|
|
* for details on soft rt detection),
|
|
* 4) these pending requests experience a high
|
|
* latency because the application is not
|
|
* weight-raised while they are pending.
|
|
*/
|
|
if (bfqq->wr_cur_max_time !=
|
|
bfqd->bfq_wr_rt_max_time) {
|
|
bfqq->wr_start_at_switch_to_srt =
|
|
bfqq->last_wr_start_finish;
|
|
|
|
bfqq->wr_cur_max_time =
|
|
bfqd->bfq_wr_rt_max_time;
|
|
bfqq->wr_coeff = bfqd->bfq_wr_coeff *
|
|
BFQ_SOFTRT_WEIGHT_FACTOR;
|
|
}
|
|
bfqq->last_wr_start_finish = jiffies;
|
|
}
|
|
}
|
|
}
|
|
|
|
static bool bfq_bfqq_idle_for_long_time(struct bfq_data *bfqd,
|
|
struct bfq_queue *bfqq)
|
|
{
|
|
return bfqq->dispatched == 0 &&
|
|
time_is_before_jiffies(
|
|
bfqq->budget_timeout +
|
|
bfqd->bfq_wr_min_idle_time);
|
|
}
|
|
|
|
static void bfq_bfqq_handle_idle_busy_switch(struct bfq_data *bfqd,
|
|
struct bfq_queue *bfqq,
|
|
int old_wr_coeff,
|
|
struct request *rq,
|
|
bool *interactive)
|
|
{
|
|
bool soft_rt, in_burst, wr_or_deserves_wr,
|
|
bfqq_wants_to_preempt,
|
|
idle_for_long_time = bfq_bfqq_idle_for_long_time(bfqd, bfqq),
|
|
/*
|
|
* See the comments on
|
|
* bfq_bfqq_update_budg_for_activation for
|
|
* details on the usage of the next variable.
|
|
*/
|
|
arrived_in_time = ktime_get_ns() <=
|
|
bfqq->ttime.last_end_request +
|
|
bfqd->bfq_slice_idle * 3;
|
|
|
|
bfqg_stats_update_io_add(bfqq_group(RQ_BFQQ(rq)), bfqq, rq->cmd_flags);
|
|
|
|
/*
|
|
* bfqq deserves to be weight-raised if:
|
|
* - it is sync,
|
|
* - it does not belong to a large burst,
|
|
* - it has been idle for enough time or is soft real-time,
|
|
* - is linked to a bfq_io_cq (it is not shared in any sense).
|
|
*/
|
|
in_burst = bfq_bfqq_in_large_burst(bfqq);
|
|
soft_rt = bfqd->bfq_wr_max_softrt_rate > 0 &&
|
|
!in_burst &&
|
|
time_is_before_jiffies(bfqq->soft_rt_next_start);
|
|
*interactive = !in_burst && idle_for_long_time;
|
|
wr_or_deserves_wr = bfqd->low_latency &&
|
|
(bfqq->wr_coeff > 1 ||
|
|
(bfq_bfqq_sync(bfqq) &&
|
|
bfqq->bic && (*interactive || soft_rt)));
|
|
|
|
/*
|
|
* Using the last flag, update budget and check whether bfqq
|
|
* may want to preempt the in-service queue.
|
|
*/
|
|
bfqq_wants_to_preempt =
|
|
bfq_bfqq_update_budg_for_activation(bfqd, bfqq,
|
|
arrived_in_time,
|
|
wr_or_deserves_wr);
|
|
|
|
/*
|
|
* If bfqq happened to be activated in a burst, but has been
|
|
* idle for much more than an interactive queue, then we
|
|
* assume that, in the overall I/O initiated in the burst, the
|
|
* I/O associated with bfqq is finished. So bfqq does not need
|
|
* to be treated as a queue belonging to a burst
|
|
* anymore. Accordingly, we reset bfqq's in_large_burst flag
|
|
* if set, and remove bfqq from the burst list if it's
|
|
* there. We do not decrement burst_size, because the fact
|
|
* that bfqq does not need to belong to the burst list any
|
|
* more does not invalidate the fact that bfqq was created in
|
|
* a burst.
|
|
*/
|
|
if (likely(!bfq_bfqq_just_created(bfqq)) &&
|
|
idle_for_long_time &&
|
|
time_is_before_jiffies(
|
|
bfqq->budget_timeout +
|
|
msecs_to_jiffies(10000))) {
|
|
hlist_del_init(&bfqq->burst_list_node);
|
|
bfq_clear_bfqq_in_large_burst(bfqq);
|
|
}
|
|
|
|
bfq_clear_bfqq_just_created(bfqq);
|
|
|
|
|
|
if (!bfq_bfqq_IO_bound(bfqq)) {
|
|
if (arrived_in_time) {
|
|
bfqq->requests_within_timer++;
|
|
if (bfqq->requests_within_timer >=
|
|
bfqd->bfq_requests_within_timer)
|
|
bfq_mark_bfqq_IO_bound(bfqq);
|
|
} else
|
|
bfqq->requests_within_timer = 0;
|
|
}
|
|
|
|
if (bfqd->low_latency) {
|
|
if (unlikely(time_is_after_jiffies(bfqq->split_time)))
|
|
/* wraparound */
|
|
bfqq->split_time =
|
|
jiffies - bfqd->bfq_wr_min_idle_time - 1;
|
|
|
|
if (time_is_before_jiffies(bfqq->split_time +
|
|
bfqd->bfq_wr_min_idle_time)) {
|
|
bfq_update_bfqq_wr_on_rq_arrival(bfqd, bfqq,
|
|
old_wr_coeff,
|
|
wr_or_deserves_wr,
|
|
*interactive,
|
|
in_burst,
|
|
soft_rt);
|
|
|
|
if (old_wr_coeff != bfqq->wr_coeff)
|
|
bfqq->entity.prio_changed = 1;
|
|
}
|
|
}
|
|
|
|
bfqq->last_idle_bklogged = jiffies;
|
|
bfqq->service_from_backlogged = 0;
|
|
bfq_clear_bfqq_softrt_update(bfqq);
|
|
|
|
bfq_add_bfqq_busy(bfqd, bfqq);
|
|
|
|
/*
|
|
* Expire in-service queue only if preemption may be needed
|
|
* for guarantees. In this respect, the function
|
|
* next_queue_may_preempt just checks a simple, necessary
|
|
* condition, and not a sufficient condition based on
|
|
* timestamps. In fact, for the latter condition to be
|
|
* evaluated, timestamps would need first to be updated, and
|
|
* this operation is quite costly (see the comments on the
|
|
* function bfq_bfqq_update_budg_for_activation).
|
|
*/
|
|
if (bfqd->in_service_queue && bfqq_wants_to_preempt &&
|
|
bfqd->in_service_queue->wr_coeff < bfqq->wr_coeff &&
|
|
next_queue_may_preempt(bfqd))
|
|
bfq_bfqq_expire(bfqd, bfqd->in_service_queue,
|
|
false, BFQQE_PREEMPTED);
|
|
}
|
|
|
|
static void bfq_add_request(struct request *rq)
|
|
{
|
|
struct bfq_queue *bfqq = RQ_BFQQ(rq);
|
|
struct bfq_data *bfqd = bfqq->bfqd;
|
|
struct request *next_rq, *prev;
|
|
unsigned int old_wr_coeff = bfqq->wr_coeff;
|
|
bool interactive = false;
|
|
|
|
bfq_log_bfqq(bfqd, bfqq, "add_request %d", rq_is_sync(rq));
|
|
bfqq->queued[rq_is_sync(rq)]++;
|
|
bfqd->queued++;
|
|
|
|
elv_rb_add(&bfqq->sort_list, rq);
|
|
|
|
/*
|
|
* Check if this request is a better next-serve candidate.
|
|
*/
|
|
prev = bfqq->next_rq;
|
|
next_rq = bfq_choose_req(bfqd, bfqq->next_rq, rq, bfqd->last_position);
|
|
bfqq->next_rq = next_rq;
|
|
|
|
/*
|
|
* Adjust priority tree position, if next_rq changes.
|
|
*/
|
|
if (prev != bfqq->next_rq)
|
|
bfq_pos_tree_add_move(bfqd, bfqq);
|
|
|
|
if (!bfq_bfqq_busy(bfqq)) /* switching to busy ... */
|
|
bfq_bfqq_handle_idle_busy_switch(bfqd, bfqq, old_wr_coeff,
|
|
rq, &interactive);
|
|
else {
|
|
if (bfqd->low_latency && old_wr_coeff == 1 && !rq_is_sync(rq) &&
|
|
time_is_before_jiffies(
|
|
bfqq->last_wr_start_finish +
|
|
bfqd->bfq_wr_min_inter_arr_async)) {
|
|
bfqq->wr_coeff = bfqd->bfq_wr_coeff;
|
|
bfqq->wr_cur_max_time = bfq_wr_duration(bfqd);
|
|
|
|
bfqd->wr_busy_queues++;
|
|
bfqq->entity.prio_changed = 1;
|
|
}
|
|
if (prev != bfqq->next_rq)
|
|
bfq_updated_next_req(bfqd, bfqq);
|
|
}
|
|
|
|
/*
|
|
* Assign jiffies to last_wr_start_finish in the following
|
|
* cases:
|
|
*
|
|
* . if bfqq is not going to be weight-raised, because, for
|
|
* non weight-raised queues, last_wr_start_finish stores the
|
|
* arrival time of the last request; as of now, this piece
|
|
* of information is used only for deciding whether to
|
|
* weight-raise async queues
|
|
*
|
|
* . if bfqq is not weight-raised, because, if bfqq is now
|
|
* switching to weight-raised, then last_wr_start_finish
|
|
* stores the time when weight-raising starts
|
|
*
|
|
* . if bfqq is interactive, because, regardless of whether
|
|
* bfqq is currently weight-raised, the weight-raising
|
|
* period must start or restart (this case is considered
|
|
* separately because it is not detected by the above
|
|
* conditions, if bfqq is already weight-raised)
|
|
*
|
|
* last_wr_start_finish has to be updated also if bfqq is soft
|
|
* real-time, because the weight-raising period is constantly
|
|
* restarted on idle-to-busy transitions for these queues, but
|
|
* this is already done in bfq_bfqq_handle_idle_busy_switch if
|
|
* needed.
|
|
*/
|
|
if (bfqd->low_latency &&
|
|
(old_wr_coeff == 1 || bfqq->wr_coeff == 1 || interactive))
|
|
bfqq->last_wr_start_finish = jiffies;
|
|
}
|
|
|
|
static struct request *bfq_find_rq_fmerge(struct bfq_data *bfqd,
|
|
struct bio *bio,
|
|
struct request_queue *q)
|
|
{
|
|
struct bfq_queue *bfqq = bfqd->bio_bfqq;
|
|
|
|
|
|
if (bfqq)
|
|
return elv_rb_find(&bfqq->sort_list, bio_end_sector(bio));
|
|
|
|
return NULL;
|
|
}
|
|
|
|
static sector_t get_sdist(sector_t last_pos, struct request *rq)
|
|
{
|
|
if (last_pos)
|
|
return abs(blk_rq_pos(rq) - last_pos);
|
|
|
|
return 0;
|
|
}
|
|
|
|
#if 0 /* Still not clear if we can do without next two functions */
|
|
static void bfq_activate_request(struct request_queue *q, struct request *rq)
|
|
{
|
|
struct bfq_data *bfqd = q->elevator->elevator_data;
|
|
|
|
bfqd->rq_in_driver++;
|
|
}
|
|
|
|
static void bfq_deactivate_request(struct request_queue *q, struct request *rq)
|
|
{
|
|
struct bfq_data *bfqd = q->elevator->elevator_data;
|
|
|
|
bfqd->rq_in_driver--;
|
|
}
|
|
#endif
|
|
|
|
static void bfq_remove_request(struct request_queue *q,
|
|
struct request *rq)
|
|
{
|
|
struct bfq_queue *bfqq = RQ_BFQQ(rq);
|
|
struct bfq_data *bfqd = bfqq->bfqd;
|
|
const int sync = rq_is_sync(rq);
|
|
|
|
if (bfqq->next_rq == rq) {
|
|
bfqq->next_rq = bfq_find_next_rq(bfqd, bfqq, rq);
|
|
bfq_updated_next_req(bfqd, bfqq);
|
|
}
|
|
|
|
if (rq->queuelist.prev != &rq->queuelist)
|
|
list_del_init(&rq->queuelist);
|
|
bfqq->queued[sync]--;
|
|
bfqd->queued--;
|
|
elv_rb_del(&bfqq->sort_list, rq);
|
|
|
|
elv_rqhash_del(q, rq);
|
|
if (q->last_merge == rq)
|
|
q->last_merge = NULL;
|
|
|
|
if (RB_EMPTY_ROOT(&bfqq->sort_list)) {
|
|
bfqq->next_rq = NULL;
|
|
|
|
if (bfq_bfqq_busy(bfqq) && bfqq != bfqd->in_service_queue) {
|
|
bfq_del_bfqq_busy(bfqd, bfqq, false);
|
|
/*
|
|
* bfqq emptied. In normal operation, when
|
|
* bfqq is empty, bfqq->entity.service and
|
|
* bfqq->entity.budget must contain,
|
|
* respectively, the service received and the
|
|
* budget used last time bfqq emptied. These
|
|
* facts do not hold in this case, as at least
|
|
* this last removal occurred while bfqq is
|
|
* not in service. To avoid inconsistencies,
|
|
* reset both bfqq->entity.service and
|
|
* bfqq->entity.budget, if bfqq has still a
|
|
* process that may issue I/O requests to it.
|
|
*/
|
|
bfqq->entity.budget = bfqq->entity.service = 0;
|
|
}
|
|
|
|
/*
|
|
* Remove queue from request-position tree as it is empty.
|
|
*/
|
|
if (bfqq->pos_root) {
|
|
rb_erase(&bfqq->pos_node, bfqq->pos_root);
|
|
bfqq->pos_root = NULL;
|
|
}
|
|
}
|
|
|
|
if (rq->cmd_flags & REQ_META)
|
|
bfqq->meta_pending--;
|
|
|
|
bfqg_stats_update_io_remove(bfqq_group(bfqq), rq->cmd_flags);
|
|
}
|
|
|
|
static bool bfq_bio_merge(struct blk_mq_hw_ctx *hctx, struct bio *bio)
|
|
{
|
|
struct request_queue *q = hctx->queue;
|
|
struct bfq_data *bfqd = q->elevator->elevator_data;
|
|
struct request *free = NULL;
|
|
/*
|
|
* bfq_bic_lookup grabs the queue_lock: invoke it now and
|
|
* store its return value for later use, to avoid nesting
|
|
* queue_lock inside the bfqd->lock. We assume that the bic
|
|
* returned by bfq_bic_lookup does not go away before
|
|
* bfqd->lock is taken.
|
|
*/
|
|
struct bfq_io_cq *bic = bfq_bic_lookup(bfqd, current->io_context, q);
|
|
bool ret;
|
|
|
|
spin_lock_irq(&bfqd->lock);
|
|
|
|
if (bic)
|
|
bfqd->bio_bfqq = bic_to_bfqq(bic, op_is_sync(bio->bi_opf));
|
|
else
|
|
bfqd->bio_bfqq = NULL;
|
|
bfqd->bio_bic = bic;
|
|
|
|
ret = blk_mq_sched_try_merge(q, bio, &free);
|
|
|
|
if (free)
|
|
blk_mq_free_request(free);
|
|
spin_unlock_irq(&bfqd->lock);
|
|
|
|
return ret;
|
|
}
|
|
|
|
static int bfq_request_merge(struct request_queue *q, struct request **req,
|
|
struct bio *bio)
|
|
{
|
|
struct bfq_data *bfqd = q->elevator->elevator_data;
|
|
struct request *__rq;
|
|
|
|
__rq = bfq_find_rq_fmerge(bfqd, bio, q);
|
|
if (__rq && elv_bio_merge_ok(__rq, bio)) {
|
|
*req = __rq;
|
|
return ELEVATOR_FRONT_MERGE;
|
|
}
|
|
|
|
return ELEVATOR_NO_MERGE;
|
|
}
|
|
|
|
static void bfq_request_merged(struct request_queue *q, struct request *req,
|
|
enum elv_merge type)
|
|
{
|
|
if (type == ELEVATOR_FRONT_MERGE &&
|
|
rb_prev(&req->rb_node) &&
|
|
blk_rq_pos(req) <
|
|
blk_rq_pos(container_of(rb_prev(&req->rb_node),
|
|
struct request, rb_node))) {
|
|
struct bfq_queue *bfqq = RQ_BFQQ(req);
|
|
struct bfq_data *bfqd = bfqq->bfqd;
|
|
struct request *prev, *next_rq;
|
|
|
|
/* Reposition request in its sort_list */
|
|
elv_rb_del(&bfqq->sort_list, req);
|
|
elv_rb_add(&bfqq->sort_list, req);
|
|
|
|
/* Choose next request to be served for bfqq */
|
|
prev = bfqq->next_rq;
|
|
next_rq = bfq_choose_req(bfqd, bfqq->next_rq, req,
|
|
bfqd->last_position);
|
|
bfqq->next_rq = next_rq;
|
|
/*
|
|
* If next_rq changes, update both the queue's budget to
|
|
* fit the new request and the queue's position in its
|
|
* rq_pos_tree.
|
|
*/
|
|
if (prev != bfqq->next_rq) {
|
|
bfq_updated_next_req(bfqd, bfqq);
|
|
bfq_pos_tree_add_move(bfqd, bfqq);
|
|
}
|
|
}
|
|
}
|
|
|
|
static void bfq_requests_merged(struct request_queue *q, struct request *rq,
|
|
struct request *next)
|
|
{
|
|
struct bfq_queue *bfqq = RQ_BFQQ(rq), *next_bfqq = RQ_BFQQ(next);
|
|
|
|
if (!RB_EMPTY_NODE(&rq->rb_node))
|
|
goto end;
|
|
spin_lock_irq(&bfqq->bfqd->lock);
|
|
|
|
/*
|
|
* If next and rq belong to the same bfq_queue and next is older
|
|
* than rq, then reposition rq in the fifo (by substituting next
|
|
* with rq). Otherwise, if next and rq belong to different
|
|
* bfq_queues, never reposition rq: in fact, we would have to
|
|
* reposition it with respect to next's position in its own fifo,
|
|
* which would most certainly be too expensive with respect to
|
|
* the benefits.
|
|
*/
|
|
if (bfqq == next_bfqq &&
|
|
!list_empty(&rq->queuelist) && !list_empty(&next->queuelist) &&
|
|
next->fifo_time < rq->fifo_time) {
|
|
list_del_init(&rq->queuelist);
|
|
list_replace_init(&next->queuelist, &rq->queuelist);
|
|
rq->fifo_time = next->fifo_time;
|
|
}
|
|
|
|
if (bfqq->next_rq == next)
|
|
bfqq->next_rq = rq;
|
|
|
|
bfq_remove_request(q, next);
|
|
|
|
spin_unlock_irq(&bfqq->bfqd->lock);
|
|
end:
|
|
bfqg_stats_update_io_merged(bfqq_group(bfqq), next->cmd_flags);
|
|
}
|
|
|
|
/* Must be called with bfqq != NULL */
|
|
static void bfq_bfqq_end_wr(struct bfq_queue *bfqq)
|
|
{
|
|
if (bfq_bfqq_busy(bfqq))
|
|
bfqq->bfqd->wr_busy_queues--;
|
|
bfqq->wr_coeff = 1;
|
|
bfqq->wr_cur_max_time = 0;
|
|
bfqq->last_wr_start_finish = jiffies;
|
|
/*
|
|
* Trigger a weight change on the next invocation of
|
|
* __bfq_entity_update_weight_prio.
|
|
*/
|
|
bfqq->entity.prio_changed = 1;
|
|
}
|
|
|
|
void bfq_end_wr_async_queues(struct bfq_data *bfqd,
|
|
struct bfq_group *bfqg)
|
|
{
|
|
int i, j;
|
|
|
|
for (i = 0; i < 2; i++)
|
|
for (j = 0; j < IOPRIO_BE_NR; j++)
|
|
if (bfqg->async_bfqq[i][j])
|
|
bfq_bfqq_end_wr(bfqg->async_bfqq[i][j]);
|
|
if (bfqg->async_idle_bfqq)
|
|
bfq_bfqq_end_wr(bfqg->async_idle_bfqq);
|
|
}
|
|
|
|
static void bfq_end_wr(struct bfq_data *bfqd)
|
|
{
|
|
struct bfq_queue *bfqq;
|
|
|
|
spin_lock_irq(&bfqd->lock);
|
|
|
|
list_for_each_entry(bfqq, &bfqd->active_list, bfqq_list)
|
|
bfq_bfqq_end_wr(bfqq);
|
|
list_for_each_entry(bfqq, &bfqd->idle_list, bfqq_list)
|
|
bfq_bfqq_end_wr(bfqq);
|
|
bfq_end_wr_async(bfqd);
|
|
|
|
spin_unlock_irq(&bfqd->lock);
|
|
}
|
|
|
|
static sector_t bfq_io_struct_pos(void *io_struct, bool request)
|
|
{
|
|
if (request)
|
|
return blk_rq_pos(io_struct);
|
|
else
|
|
return ((struct bio *)io_struct)->bi_iter.bi_sector;
|
|
}
|
|
|
|
static int bfq_rq_close_to_sector(void *io_struct, bool request,
|
|
sector_t sector)
|
|
{
|
|
return abs(bfq_io_struct_pos(io_struct, request) - sector) <=
|
|
BFQQ_CLOSE_THR;
|
|
}
|
|
|
|
static struct bfq_queue *bfqq_find_close(struct bfq_data *bfqd,
|
|
struct bfq_queue *bfqq,
|
|
sector_t sector)
|
|
{
|
|
struct rb_root *root = &bfq_bfqq_to_bfqg(bfqq)->rq_pos_tree;
|
|
struct rb_node *parent, *node;
|
|
struct bfq_queue *__bfqq;
|
|
|
|
if (RB_EMPTY_ROOT(root))
|
|
return NULL;
|
|
|
|
/*
|
|
* First, if we find a request starting at the end of the last
|
|
* request, choose it.
|
|
*/
|
|
__bfqq = bfq_rq_pos_tree_lookup(bfqd, root, sector, &parent, NULL);
|
|
if (__bfqq)
|
|
return __bfqq;
|
|
|
|
/*
|
|
* If the exact sector wasn't found, the parent of the NULL leaf
|
|
* will contain the closest sector (rq_pos_tree sorted by
|
|
* next_request position).
|
|
*/
|
|
__bfqq = rb_entry(parent, struct bfq_queue, pos_node);
|
|
if (bfq_rq_close_to_sector(__bfqq->next_rq, true, sector))
|
|
return __bfqq;
|
|
|
|
if (blk_rq_pos(__bfqq->next_rq) < sector)
|
|
node = rb_next(&__bfqq->pos_node);
|
|
else
|
|
node = rb_prev(&__bfqq->pos_node);
|
|
if (!node)
|
|
return NULL;
|
|
|
|
__bfqq = rb_entry(node, struct bfq_queue, pos_node);
|
|
if (bfq_rq_close_to_sector(__bfqq->next_rq, true, sector))
|
|
return __bfqq;
|
|
|
|
return NULL;
|
|
}
|
|
|
|
static struct bfq_queue *bfq_find_close_cooperator(struct bfq_data *bfqd,
|
|
struct bfq_queue *cur_bfqq,
|
|
sector_t sector)
|
|
{
|
|
struct bfq_queue *bfqq;
|
|
|
|
/*
|
|
* We shall notice if some of the queues are cooperating,
|
|
* e.g., working closely on the same area of the device. In
|
|
* that case, we can group them together and: 1) don't waste
|
|
* time idling, and 2) serve the union of their requests in
|
|
* the best possible order for throughput.
|
|
*/
|
|
bfqq = bfqq_find_close(bfqd, cur_bfqq, sector);
|
|
if (!bfqq || bfqq == cur_bfqq)
|
|
return NULL;
|
|
|
|
return bfqq;
|
|
}
|
|
|
|
static struct bfq_queue *
|
|
bfq_setup_merge(struct bfq_queue *bfqq, struct bfq_queue *new_bfqq)
|
|
{
|
|
int process_refs, new_process_refs;
|
|
struct bfq_queue *__bfqq;
|
|
|
|
/*
|
|
* If there are no process references on the new_bfqq, then it is
|
|
* unsafe to follow the ->new_bfqq chain as other bfqq's in the chain
|
|
* may have dropped their last reference (not just their last process
|
|
* reference).
|
|
*/
|
|
if (!bfqq_process_refs(new_bfqq))
|
|
return NULL;
|
|
|
|
/* Avoid a circular list and skip interim queue merges. */
|
|
while ((__bfqq = new_bfqq->new_bfqq)) {
|
|
if (__bfqq == bfqq)
|
|
return NULL;
|
|
new_bfqq = __bfqq;
|
|
}
|
|
|
|
process_refs = bfqq_process_refs(bfqq);
|
|
new_process_refs = bfqq_process_refs(new_bfqq);
|
|
/*
|
|
* If the process for the bfqq has gone away, there is no
|
|
* sense in merging the queues.
|
|
*/
|
|
if (process_refs == 0 || new_process_refs == 0)
|
|
return NULL;
|
|
|
|
bfq_log_bfqq(bfqq->bfqd, bfqq, "scheduling merge with queue %d",
|
|
new_bfqq->pid);
|
|
|
|
/*
|
|
* Merging is just a redirection: the requests of the process
|
|
* owning one of the two queues are redirected to the other queue.
|
|
* The latter queue, in its turn, is set as shared if this is the
|
|
* first time that the requests of some process are redirected to
|
|
* it.
|
|
*
|
|
* We redirect bfqq to new_bfqq and not the opposite, because
|
|
* we are in the context of the process owning bfqq, thus we
|
|
* have the io_cq of this process. So we can immediately
|
|
* configure this io_cq to redirect the requests of the
|
|
* process to new_bfqq. In contrast, the io_cq of new_bfqq is
|
|
* not available any more (new_bfqq->bic == NULL).
|
|
*
|
|
* Anyway, even in case new_bfqq coincides with the in-service
|
|
* queue, redirecting requests the in-service queue is the
|
|
* best option, as we feed the in-service queue with new
|
|
* requests close to the last request served and, by doing so,
|
|
* are likely to increase the throughput.
|
|
*/
|
|
bfqq->new_bfqq = new_bfqq;
|
|
new_bfqq->ref += process_refs;
|
|
return new_bfqq;
|
|
}
|
|
|
|
static bool bfq_may_be_close_cooperator(struct bfq_queue *bfqq,
|
|
struct bfq_queue *new_bfqq)
|
|
{
|
|
if (bfq_class_idle(bfqq) || bfq_class_idle(new_bfqq) ||
|
|
(bfqq->ioprio_class != new_bfqq->ioprio_class))
|
|
return false;
|
|
|
|
/*
|
|
* If either of the queues has already been detected as seeky,
|
|
* then merging it with the other queue is unlikely to lead to
|
|
* sequential I/O.
|
|
*/
|
|
if (BFQQ_SEEKY(bfqq) || BFQQ_SEEKY(new_bfqq))
|
|
return false;
|
|
|
|
/*
|
|
* Interleaved I/O is known to be done by (some) applications
|
|
* only for reads, so it does not make sense to merge async
|
|
* queues.
|
|
*/
|
|
if (!bfq_bfqq_sync(bfqq) || !bfq_bfqq_sync(new_bfqq))
|
|
return false;
|
|
|
|
return true;
|
|
}
|
|
|
|
/*
|
|
* If this function returns true, then bfqq cannot be merged. The idea
|
|
* is that true cooperation happens very early after processes start
|
|
* to do I/O. Usually, late cooperations are just accidental false
|
|
* positives. In case bfqq is weight-raised, such false positives
|
|
* would evidently degrade latency guarantees for bfqq.
|
|
*/
|
|
static bool wr_from_too_long(struct bfq_queue *bfqq)
|
|
{
|
|
return bfqq->wr_coeff > 1 &&
|
|
time_is_before_jiffies(bfqq->last_wr_start_finish +
|
|
msecs_to_jiffies(100));
|
|
}
|
|
|
|
/*
|
|
* Attempt to schedule a merge of bfqq with the currently in-service
|
|
* queue or with a close queue among the scheduled queues. Return
|
|
* NULL if no merge was scheduled, a pointer to the shared bfq_queue
|
|
* structure otherwise.
|
|
*
|
|
* The OOM queue is not allowed to participate to cooperation: in fact, since
|
|
* the requests temporarily redirected to the OOM queue could be redirected
|
|
* again to dedicated queues at any time, the state needed to correctly
|
|
* handle merging with the OOM queue would be quite complex and expensive
|
|
* to maintain. Besides, in such a critical condition as an out of memory,
|
|
* the benefits of queue merging may be little relevant, or even negligible.
|
|
*
|
|
* Weight-raised queues can be merged only if their weight-raising
|
|
* period has just started. In fact cooperating processes are usually
|
|
* started together. Thus, with this filter we avoid false positives
|
|
* that would jeopardize low-latency guarantees.
|
|
*
|
|
* WARNING: queue merging may impair fairness among non-weight raised
|
|
* queues, for at least two reasons: 1) the original weight of a
|
|
* merged queue may change during the merged state, 2) even being the
|
|
* weight the same, a merged queue may be bloated with many more
|
|
* requests than the ones produced by its originally-associated
|
|
* process.
|
|
*/
|
|
static struct bfq_queue *
|
|
bfq_setup_cooperator(struct bfq_data *bfqd, struct bfq_queue *bfqq,
|
|
void *io_struct, bool request)
|
|
{
|
|
struct bfq_queue *in_service_bfqq, *new_bfqq;
|
|
|
|
if (bfqq->new_bfqq)
|
|
return bfqq->new_bfqq;
|
|
|
|
if (!io_struct ||
|
|
wr_from_too_long(bfqq) ||
|
|
unlikely(bfqq == &bfqd->oom_bfqq))
|
|
return NULL;
|
|
|
|
/* If there is only one backlogged queue, don't search. */
|
|
if (bfqd->busy_queues == 1)
|
|
return NULL;
|
|
|
|
in_service_bfqq = bfqd->in_service_queue;
|
|
|
|
if (!in_service_bfqq || in_service_bfqq == bfqq
|
|
|| wr_from_too_long(in_service_bfqq) ||
|
|
unlikely(in_service_bfqq == &bfqd->oom_bfqq))
|
|
goto check_scheduled;
|
|
|
|
if (bfq_rq_close_to_sector(io_struct, request, bfqd->last_position) &&
|
|
bfqq->entity.parent == in_service_bfqq->entity.parent &&
|
|
bfq_may_be_close_cooperator(bfqq, in_service_bfqq)) {
|
|
new_bfqq = bfq_setup_merge(bfqq, in_service_bfqq);
|
|
if (new_bfqq)
|
|
return new_bfqq;
|
|
}
|
|
/*
|
|
* Check whether there is a cooperator among currently scheduled
|
|
* queues. The only thing we need is that the bio/request is not
|
|
* NULL, as we need it to establish whether a cooperator exists.
|
|
*/
|
|
check_scheduled:
|
|
new_bfqq = bfq_find_close_cooperator(bfqd, bfqq,
|
|
bfq_io_struct_pos(io_struct, request));
|
|
|
|
if (new_bfqq && !wr_from_too_long(new_bfqq) &&
|
|
likely(new_bfqq != &bfqd->oom_bfqq) &&
|
|
bfq_may_be_close_cooperator(bfqq, new_bfqq))
|
|
return bfq_setup_merge(bfqq, new_bfqq);
|
|
|
|
return NULL;
|
|
}
|
|
|
|
static void bfq_bfqq_save_state(struct bfq_queue *bfqq)
|
|
{
|
|
struct bfq_io_cq *bic = bfqq->bic;
|
|
|
|
/*
|
|
* If !bfqq->bic, the queue is already shared or its requests
|
|
* have already been redirected to a shared queue; both idle window
|
|
* and weight raising state have already been saved. Do nothing.
|
|
*/
|
|
if (!bic)
|
|
return;
|
|
|
|
bic->saved_ttime = bfqq->ttime;
|
|
bic->saved_idle_window = bfq_bfqq_idle_window(bfqq);
|
|
bic->saved_IO_bound = bfq_bfqq_IO_bound(bfqq);
|
|
bic->saved_in_large_burst = bfq_bfqq_in_large_burst(bfqq);
|
|
bic->was_in_burst_list = !hlist_unhashed(&bfqq->burst_list_node);
|
|
bic->saved_wr_coeff = bfqq->wr_coeff;
|
|
bic->saved_wr_start_at_switch_to_srt = bfqq->wr_start_at_switch_to_srt;
|
|
bic->saved_last_wr_start_finish = bfqq->last_wr_start_finish;
|
|
bic->saved_wr_cur_max_time = bfqq->wr_cur_max_time;
|
|
}
|
|
|
|
static void
|
|
bfq_merge_bfqqs(struct bfq_data *bfqd, struct bfq_io_cq *bic,
|
|
struct bfq_queue *bfqq, struct bfq_queue *new_bfqq)
|
|
{
|
|
bfq_log_bfqq(bfqd, bfqq, "merging with queue %lu",
|
|
(unsigned long)new_bfqq->pid);
|
|
/* Save weight raising and idle window of the merged queues */
|
|
bfq_bfqq_save_state(bfqq);
|
|
bfq_bfqq_save_state(new_bfqq);
|
|
if (bfq_bfqq_IO_bound(bfqq))
|
|
bfq_mark_bfqq_IO_bound(new_bfqq);
|
|
bfq_clear_bfqq_IO_bound(bfqq);
|
|
|
|
/*
|
|
* If bfqq is weight-raised, then let new_bfqq inherit
|
|
* weight-raising. To reduce false positives, neglect the case
|
|
* where bfqq has just been created, but has not yet made it
|
|
* to be weight-raised (which may happen because EQM may merge
|
|
* bfqq even before bfq_add_request is executed for the first
|
|
* time for bfqq). Handling this case would however be very
|
|
* easy, thanks to the flag just_created.
|
|
*/
|
|
if (new_bfqq->wr_coeff == 1 && bfqq->wr_coeff > 1) {
|
|
new_bfqq->wr_coeff = bfqq->wr_coeff;
|
|
new_bfqq->wr_cur_max_time = bfqq->wr_cur_max_time;
|
|
new_bfqq->last_wr_start_finish = bfqq->last_wr_start_finish;
|
|
new_bfqq->wr_start_at_switch_to_srt =
|
|
bfqq->wr_start_at_switch_to_srt;
|
|
if (bfq_bfqq_busy(new_bfqq))
|
|
bfqd->wr_busy_queues++;
|
|
new_bfqq->entity.prio_changed = 1;
|
|
}
|
|
|
|
if (bfqq->wr_coeff > 1) { /* bfqq has given its wr to new_bfqq */
|
|
bfqq->wr_coeff = 1;
|
|
bfqq->entity.prio_changed = 1;
|
|
if (bfq_bfqq_busy(bfqq))
|
|
bfqd->wr_busy_queues--;
|
|
}
|
|
|
|
bfq_log_bfqq(bfqd, new_bfqq, "merge_bfqqs: wr_busy %d",
|
|
bfqd->wr_busy_queues);
|
|
|
|
/*
|
|
* Merge queues (that is, let bic redirect its requests to new_bfqq)
|
|
*/
|
|
bic_set_bfqq(bic, new_bfqq, 1);
|
|
bfq_mark_bfqq_coop(new_bfqq);
|
|
/*
|
|
* new_bfqq now belongs to at least two bics (it is a shared queue):
|
|
* set new_bfqq->bic to NULL. bfqq either:
|
|
* - does not belong to any bic any more, and hence bfqq->bic must
|
|
* be set to NULL, or
|
|
* - is a queue whose owning bics have already been redirected to a
|
|
* different queue, hence the queue is destined to not belong to
|
|
* any bic soon and bfqq->bic is already NULL (therefore the next
|
|
* assignment causes no harm).
|
|
*/
|
|
new_bfqq->bic = NULL;
|
|
bfqq->bic = NULL;
|
|
/* release process reference to bfqq */
|
|
bfq_put_queue(bfqq);
|
|
}
|
|
|
|
static bool bfq_allow_bio_merge(struct request_queue *q, struct request *rq,
|
|
struct bio *bio)
|
|
{
|
|
struct bfq_data *bfqd = q->elevator->elevator_data;
|
|
bool is_sync = op_is_sync(bio->bi_opf);
|
|
struct bfq_queue *bfqq = bfqd->bio_bfqq, *new_bfqq;
|
|
|
|
/*
|
|
* Disallow merge of a sync bio into an async request.
|
|
*/
|
|
if (is_sync && !rq_is_sync(rq))
|
|
return false;
|
|
|
|
/*
|
|
* Lookup the bfqq that this bio will be queued with. Allow
|
|
* merge only if rq is queued there.
|
|
*/
|
|
if (!bfqq)
|
|
return false;
|
|
|
|
/*
|
|
* We take advantage of this function to perform an early merge
|
|
* of the queues of possible cooperating processes.
|
|
*/
|
|
new_bfqq = bfq_setup_cooperator(bfqd, bfqq, bio, false);
|
|
if (new_bfqq) {
|
|
/*
|
|
* bic still points to bfqq, then it has not yet been
|
|
* redirected to some other bfq_queue, and a queue
|
|
* merge beween bfqq and new_bfqq can be safely
|
|
* fulfillled, i.e., bic can be redirected to new_bfqq
|
|
* and bfqq can be put.
|
|
*/
|
|
bfq_merge_bfqqs(bfqd, bfqd->bio_bic, bfqq,
|
|
new_bfqq);
|
|
/*
|
|
* If we get here, bio will be queued into new_queue,
|
|
* so use new_bfqq to decide whether bio and rq can be
|
|
* merged.
|
|
*/
|
|
bfqq = new_bfqq;
|
|
|
|
/*
|
|
* Change also bqfd->bio_bfqq, as
|
|
* bfqd->bio_bic now points to new_bfqq, and
|
|
* this function may be invoked again (and then may
|
|
* use again bqfd->bio_bfqq).
|
|
*/
|
|
bfqd->bio_bfqq = bfqq;
|
|
}
|
|
|
|
return bfqq == RQ_BFQQ(rq);
|
|
}
|
|
|
|
/*
|
|
* Set the maximum time for the in-service queue to consume its
|
|
* budget. This prevents seeky processes from lowering the throughput.
|
|
* In practice, a time-slice service scheme is used with seeky
|
|
* processes.
|
|
*/
|
|
static void bfq_set_budget_timeout(struct bfq_data *bfqd,
|
|
struct bfq_queue *bfqq)
|
|
{
|
|
unsigned int timeout_coeff;
|
|
|
|
if (bfqq->wr_cur_max_time == bfqd->bfq_wr_rt_max_time)
|
|
timeout_coeff = 1;
|
|
else
|
|
timeout_coeff = bfqq->entity.weight / bfqq->entity.orig_weight;
|
|
|
|
bfqd->last_budget_start = ktime_get();
|
|
|
|
bfqq->budget_timeout = jiffies +
|
|
bfqd->bfq_timeout * timeout_coeff;
|
|
}
|
|
|
|
static void __bfq_set_in_service_queue(struct bfq_data *bfqd,
|
|
struct bfq_queue *bfqq)
|
|
{
|
|
if (bfqq) {
|
|
bfqg_stats_update_avg_queue_size(bfqq_group(bfqq));
|
|
bfq_clear_bfqq_fifo_expire(bfqq);
|
|
|
|
bfqd->budgets_assigned = (bfqd->budgets_assigned * 7 + 256) / 8;
|
|
|
|
if (time_is_before_jiffies(bfqq->last_wr_start_finish) &&
|
|
bfqq->wr_coeff > 1 &&
|
|
bfqq->wr_cur_max_time == bfqd->bfq_wr_rt_max_time &&
|
|
time_is_before_jiffies(bfqq->budget_timeout)) {
|
|
/*
|
|
* For soft real-time queues, move the start
|
|
* of the weight-raising period forward by the
|
|
* time the queue has not received any
|
|
* service. Otherwise, a relatively long
|
|
* service delay is likely to cause the
|
|
* weight-raising period of the queue to end,
|
|
* because of the short duration of the
|
|
* weight-raising period of a soft real-time
|
|
* queue. It is worth noting that this move
|
|
* is not so dangerous for the other queues,
|
|
* because soft real-time queues are not
|
|
* greedy.
|
|
*
|
|
* To not add a further variable, we use the
|
|
* overloaded field budget_timeout to
|
|
* determine for how long the queue has not
|
|
* received service, i.e., how much time has
|
|
* elapsed since the queue expired. However,
|
|
* this is a little imprecise, because
|
|
* budget_timeout is set to jiffies if bfqq
|
|
* not only expires, but also remains with no
|
|
* request.
|
|
*/
|
|
if (time_after(bfqq->budget_timeout,
|
|
bfqq->last_wr_start_finish))
|
|
bfqq->last_wr_start_finish +=
|
|
jiffies - bfqq->budget_timeout;
|
|
else
|
|
bfqq->last_wr_start_finish = jiffies;
|
|
}
|
|
|
|
bfq_set_budget_timeout(bfqd, bfqq);
|
|
bfq_log_bfqq(bfqd, bfqq,
|
|
"set_in_service_queue, cur-budget = %d",
|
|
bfqq->entity.budget);
|
|
}
|
|
|
|
bfqd->in_service_queue = bfqq;
|
|
}
|
|
|
|
/*
|
|
* Get and set a new queue for service.
|
|
*/
|
|
static struct bfq_queue *bfq_set_in_service_queue(struct bfq_data *bfqd)
|
|
{
|
|
struct bfq_queue *bfqq = bfq_get_next_queue(bfqd);
|
|
|
|
__bfq_set_in_service_queue(bfqd, bfqq);
|
|
return bfqq;
|
|
}
|
|
|
|
static void bfq_arm_slice_timer(struct bfq_data *bfqd)
|
|
{
|
|
struct bfq_queue *bfqq = bfqd->in_service_queue;
|
|
u32 sl;
|
|
|
|
bfq_mark_bfqq_wait_request(bfqq);
|
|
|
|
/*
|
|
* We don't want to idle for seeks, but we do want to allow
|
|
* fair distribution of slice time for a process doing back-to-back
|
|
* seeks. So allow a little bit of time for him to submit a new rq.
|
|
*/
|
|
sl = bfqd->bfq_slice_idle;
|
|
/*
|
|
* Unless the queue is being weight-raised or the scenario is
|
|
* asymmetric, grant only minimum idle time if the queue
|
|
* is seeky. A long idling is preserved for a weight-raised
|
|
* queue, or, more in general, in an asymmetric scenario,
|
|
* because a long idling is needed for guaranteeing to a queue
|
|
* its reserved share of the throughput (in particular, it is
|
|
* needed if the queue has a higher weight than some other
|
|
* queue).
|
|
*/
|
|
if (BFQQ_SEEKY(bfqq) && bfqq->wr_coeff == 1 &&
|
|
bfq_symmetric_scenario(bfqd))
|
|
sl = min_t(u64, sl, BFQ_MIN_TT);
|
|
|
|
bfqd->last_idling_start = ktime_get();
|
|
hrtimer_start(&bfqd->idle_slice_timer, ns_to_ktime(sl),
|
|
HRTIMER_MODE_REL);
|
|
bfqg_stats_set_start_idle_time(bfqq_group(bfqq));
|
|
}
|
|
|
|
/*
|
|
* In autotuning mode, max_budget is dynamically recomputed as the
|
|
* amount of sectors transferred in timeout at the estimated peak
|
|
* rate. This enables BFQ to utilize a full timeslice with a full
|
|
* budget, even if the in-service queue is served at peak rate. And
|
|
* this maximises throughput with sequential workloads.
|
|
*/
|
|
static unsigned long bfq_calc_max_budget(struct bfq_data *bfqd)
|
|
{
|
|
return (u64)bfqd->peak_rate * USEC_PER_MSEC *
|
|
jiffies_to_msecs(bfqd->bfq_timeout)>>BFQ_RATE_SHIFT;
|
|
}
|
|
|
|
/*
|
|
* Update parameters related to throughput and responsiveness, as a
|
|
* function of the estimated peak rate. See comments on
|
|
* bfq_calc_max_budget(), and on T_slow and T_fast arrays.
|
|
*/
|
|
static void update_thr_responsiveness_params(struct bfq_data *bfqd)
|
|
{
|
|
int dev_type = blk_queue_nonrot(bfqd->queue);
|
|
|
|
if (bfqd->bfq_user_max_budget == 0)
|
|
bfqd->bfq_max_budget =
|
|
bfq_calc_max_budget(bfqd);
|
|
|
|
if (bfqd->device_speed == BFQ_BFQD_FAST &&
|
|
bfqd->peak_rate < device_speed_thresh[dev_type]) {
|
|
bfqd->device_speed = BFQ_BFQD_SLOW;
|
|
bfqd->RT_prod = R_slow[dev_type] *
|
|
T_slow[dev_type];
|
|
} else if (bfqd->device_speed == BFQ_BFQD_SLOW &&
|
|
bfqd->peak_rate > device_speed_thresh[dev_type]) {
|
|
bfqd->device_speed = BFQ_BFQD_FAST;
|
|
bfqd->RT_prod = R_fast[dev_type] *
|
|
T_fast[dev_type];
|
|
}
|
|
|
|
bfq_log(bfqd,
|
|
"dev_type %s dev_speed_class = %s (%llu sects/sec), thresh %llu setcs/sec",
|
|
dev_type == 0 ? "ROT" : "NONROT",
|
|
bfqd->device_speed == BFQ_BFQD_FAST ? "FAST" : "SLOW",
|
|
bfqd->device_speed == BFQ_BFQD_FAST ?
|
|
(USEC_PER_SEC*(u64)R_fast[dev_type])>>BFQ_RATE_SHIFT :
|
|
(USEC_PER_SEC*(u64)R_slow[dev_type])>>BFQ_RATE_SHIFT,
|
|
(USEC_PER_SEC*(u64)device_speed_thresh[dev_type])>>
|
|
BFQ_RATE_SHIFT);
|
|
}
|
|
|
|
static void bfq_reset_rate_computation(struct bfq_data *bfqd,
|
|
struct request *rq)
|
|
{
|
|
if (rq != NULL) { /* new rq dispatch now, reset accordingly */
|
|
bfqd->last_dispatch = bfqd->first_dispatch = ktime_get_ns();
|
|
bfqd->peak_rate_samples = 1;
|
|
bfqd->sequential_samples = 0;
|
|
bfqd->tot_sectors_dispatched = bfqd->last_rq_max_size =
|
|
blk_rq_sectors(rq);
|
|
} else /* no new rq dispatched, just reset the number of samples */
|
|
bfqd->peak_rate_samples = 0; /* full re-init on next disp. */
|
|
|
|
bfq_log(bfqd,
|
|
"reset_rate_computation at end, sample %u/%u tot_sects %llu",
|
|
bfqd->peak_rate_samples, bfqd->sequential_samples,
|
|
bfqd->tot_sectors_dispatched);
|
|
}
|
|
|
|
static void bfq_update_rate_reset(struct bfq_data *bfqd, struct request *rq)
|
|
{
|
|
u32 rate, weight, divisor;
|
|
|
|
/*
|
|
* For the convergence property to hold (see comments on
|
|
* bfq_update_peak_rate()) and for the assessment to be
|
|
* reliable, a minimum number of samples must be present, and
|
|
* a minimum amount of time must have elapsed. If not so, do
|
|
* not compute new rate. Just reset parameters, to get ready
|
|
* for a new evaluation attempt.
|
|
*/
|
|
if (bfqd->peak_rate_samples < BFQ_RATE_MIN_SAMPLES ||
|
|
bfqd->delta_from_first < BFQ_RATE_MIN_INTERVAL)
|
|
goto reset_computation;
|
|
|
|
/*
|
|
* If a new request completion has occurred after last
|
|
* dispatch, then, to approximate the rate at which requests
|
|
* have been served by the device, it is more precise to
|
|
* extend the observation interval to the last completion.
|
|
*/
|
|
bfqd->delta_from_first =
|
|
max_t(u64, bfqd->delta_from_first,
|
|
bfqd->last_completion - bfqd->first_dispatch);
|
|
|
|
/*
|
|
* Rate computed in sects/usec, and not sects/nsec, for
|
|
* precision issues.
|
|
*/
|
|
rate = div64_ul(bfqd->tot_sectors_dispatched<<BFQ_RATE_SHIFT,
|
|
div_u64(bfqd->delta_from_first, NSEC_PER_USEC));
|
|
|
|
/*
|
|
* Peak rate not updated if:
|
|
* - the percentage of sequential dispatches is below 3/4 of the
|
|
* total, and rate is below the current estimated peak rate
|
|
* - rate is unreasonably high (> 20M sectors/sec)
|
|
*/
|
|
if ((bfqd->sequential_samples < (3 * bfqd->peak_rate_samples)>>2 &&
|
|
rate <= bfqd->peak_rate) ||
|
|
rate > 20<<BFQ_RATE_SHIFT)
|
|
goto reset_computation;
|
|
|
|
/*
|
|
* We have to update the peak rate, at last! To this purpose,
|
|
* we use a low-pass filter. We compute the smoothing constant
|
|
* of the filter as a function of the 'weight' of the new
|
|
* measured rate.
|
|
*
|
|
* As can be seen in next formulas, we define this weight as a
|
|
* quantity proportional to how sequential the workload is,
|
|
* and to how long the observation time interval is.
|
|
*
|
|
* The weight runs from 0 to 8. The maximum value of the
|
|
* weight, 8, yields the minimum value for the smoothing
|
|
* constant. At this minimum value for the smoothing constant,
|
|
* the measured rate contributes for half of the next value of
|
|
* the estimated peak rate.
|
|
*
|
|
* So, the first step is to compute the weight as a function
|
|
* of how sequential the workload is. Note that the weight
|
|
* cannot reach 9, because bfqd->sequential_samples cannot
|
|
* become equal to bfqd->peak_rate_samples, which, in its
|
|
* turn, holds true because bfqd->sequential_samples is not
|
|
* incremented for the first sample.
|
|
*/
|
|
weight = (9 * bfqd->sequential_samples) / bfqd->peak_rate_samples;
|
|
|
|
/*
|
|
* Second step: further refine the weight as a function of the
|
|
* duration of the observation interval.
|
|
*/
|
|
weight = min_t(u32, 8,
|
|
div_u64(weight * bfqd->delta_from_first,
|
|
BFQ_RATE_REF_INTERVAL));
|
|
|
|
/*
|
|
* Divisor ranging from 10, for minimum weight, to 2, for
|
|
* maximum weight.
|
|
*/
|
|
divisor = 10 - weight;
|
|
|
|
/*
|
|
* Finally, update peak rate:
|
|
*
|
|
* peak_rate = peak_rate * (divisor-1) / divisor + rate / divisor
|
|
*/
|
|
bfqd->peak_rate *= divisor-1;
|
|
bfqd->peak_rate /= divisor;
|
|
rate /= divisor; /* smoothing constant alpha = 1/divisor */
|
|
|
|
bfqd->peak_rate += rate;
|
|
update_thr_responsiveness_params(bfqd);
|
|
|
|
reset_computation:
|
|
bfq_reset_rate_computation(bfqd, rq);
|
|
}
|
|
|
|
/*
|
|
* Update the read/write peak rate (the main quantity used for
|
|
* auto-tuning, see update_thr_responsiveness_params()).
|
|
*
|
|
* It is not trivial to estimate the peak rate (correctly): because of
|
|
* the presence of sw and hw queues between the scheduler and the
|
|
* device components that finally serve I/O requests, it is hard to
|
|
* say exactly when a given dispatched request is served inside the
|
|
* device, and for how long. As a consequence, it is hard to know
|
|
* precisely at what rate a given set of requests is actually served
|
|
* by the device.
|
|
*
|
|
* On the opposite end, the dispatch time of any request is trivially
|
|
* available, and, from this piece of information, the "dispatch rate"
|
|
* of requests can be immediately computed. So, the idea in the next
|
|
* function is to use what is known, namely request dispatch times
|
|
* (plus, when useful, request completion times), to estimate what is
|
|
* unknown, namely in-device request service rate.
|
|
*
|
|
* The main issue is that, because of the above facts, the rate at
|
|
* which a certain set of requests is dispatched over a certain time
|
|
* interval can vary greatly with respect to the rate at which the
|
|
* same requests are then served. But, since the size of any
|
|
* intermediate queue is limited, and the service scheme is lossless
|
|
* (no request is silently dropped), the following obvious convergence
|
|
* property holds: the number of requests dispatched MUST become
|
|
* closer and closer to the number of requests completed as the
|
|
* observation interval grows. This is the key property used in
|
|
* the next function to estimate the peak service rate as a function
|
|
* of the observed dispatch rate. The function assumes to be invoked
|
|
* on every request dispatch.
|
|
*/
|
|
static void bfq_update_peak_rate(struct bfq_data *bfqd, struct request *rq)
|
|
{
|
|
u64 now_ns = ktime_get_ns();
|
|
|
|
if (bfqd->peak_rate_samples == 0) { /* first dispatch */
|
|
bfq_log(bfqd, "update_peak_rate: goto reset, samples %d",
|
|
bfqd->peak_rate_samples);
|
|
bfq_reset_rate_computation(bfqd, rq);
|
|
goto update_last_values; /* will add one sample */
|
|
}
|
|
|
|
/*
|
|
* Device idle for very long: the observation interval lasting
|
|
* up to this dispatch cannot be a valid observation interval
|
|
* for computing a new peak rate (similarly to the late-
|
|
* completion event in bfq_completed_request()). Go to
|
|
* update_rate_and_reset to have the following three steps
|
|
* taken:
|
|
* - close the observation interval at the last (previous)
|
|
* request dispatch or completion
|
|
* - compute rate, if possible, for that observation interval
|
|
* - start a new observation interval with this dispatch
|
|
*/
|
|
if (now_ns - bfqd->last_dispatch > 100*NSEC_PER_MSEC &&
|
|
bfqd->rq_in_driver == 0)
|
|
goto update_rate_and_reset;
|
|
|
|
/* Update sampling information */
|
|
bfqd->peak_rate_samples++;
|
|
|
|
if ((bfqd->rq_in_driver > 0 ||
|
|
now_ns - bfqd->last_completion < BFQ_MIN_TT)
|
|
&& get_sdist(bfqd->last_position, rq) < BFQQ_SEEK_THR)
|
|
bfqd->sequential_samples++;
|
|
|
|
bfqd->tot_sectors_dispatched += blk_rq_sectors(rq);
|
|
|
|
/* Reset max observed rq size every 32 dispatches */
|
|
if (likely(bfqd->peak_rate_samples % 32))
|
|
bfqd->last_rq_max_size =
|
|
max_t(u32, blk_rq_sectors(rq), bfqd->last_rq_max_size);
|
|
else
|
|
bfqd->last_rq_max_size = blk_rq_sectors(rq);
|
|
|
|
bfqd->delta_from_first = now_ns - bfqd->first_dispatch;
|
|
|
|
/* Target observation interval not yet reached, go on sampling */
|
|
if (bfqd->delta_from_first < BFQ_RATE_REF_INTERVAL)
|
|
goto update_last_values;
|
|
|
|
update_rate_and_reset:
|
|
bfq_update_rate_reset(bfqd, rq);
|
|
update_last_values:
|
|
bfqd->last_position = blk_rq_pos(rq) + blk_rq_sectors(rq);
|
|
bfqd->last_dispatch = now_ns;
|
|
}
|
|
|
|
/*
|
|
* Remove request from internal lists.
|
|
*/
|
|
static void bfq_dispatch_remove(struct request_queue *q, struct request *rq)
|
|
{
|
|
struct bfq_queue *bfqq = RQ_BFQQ(rq);
|
|
|
|
/*
|
|
* For consistency, the next instruction should have been
|
|
* executed after removing the request from the queue and
|
|
* dispatching it. We execute instead this instruction before
|
|
* bfq_remove_request() (and hence introduce a temporary
|
|
* inconsistency), for efficiency. In fact, should this
|
|
* dispatch occur for a non in-service bfqq, this anticipated
|
|
* increment prevents two counters related to bfqq->dispatched
|
|
* from risking to be, first, uselessly decremented, and then
|
|
* incremented again when the (new) value of bfqq->dispatched
|
|
* happens to be taken into account.
|
|
*/
|
|
bfqq->dispatched++;
|
|
bfq_update_peak_rate(q->elevator->elevator_data, rq);
|
|
|
|
bfq_remove_request(q, rq);
|
|
}
|
|
|
|
static void __bfq_bfqq_expire(struct bfq_data *bfqd, struct bfq_queue *bfqq)
|
|
{
|
|
/*
|
|
* If this bfqq is shared between multiple processes, check
|
|
* to make sure that those processes are still issuing I/Os
|
|
* within the mean seek distance. If not, it may be time to
|
|
* break the queues apart again.
|
|
*/
|
|
if (bfq_bfqq_coop(bfqq) && BFQQ_SEEKY(bfqq))
|
|
bfq_mark_bfqq_split_coop(bfqq);
|
|
|
|
if (RB_EMPTY_ROOT(&bfqq->sort_list)) {
|
|
if (bfqq->dispatched == 0)
|
|
/*
|
|
* Overloading budget_timeout field to store
|
|
* the time at which the queue remains with no
|
|
* backlog and no outstanding request; used by
|
|
* the weight-raising mechanism.
|
|
*/
|
|
bfqq->budget_timeout = jiffies;
|
|
|
|
bfq_del_bfqq_busy(bfqd, bfqq, true);
|
|
} else {
|
|
bfq_requeue_bfqq(bfqd, bfqq);
|
|
/*
|
|
* Resort priority tree of potential close cooperators.
|
|
*/
|
|
bfq_pos_tree_add_move(bfqd, bfqq);
|
|
}
|
|
|
|
/*
|
|
* All in-service entities must have been properly deactivated
|
|
* or requeued before executing the next function, which
|
|
* resets all in-service entites as no more in service.
|
|
*/
|
|
__bfq_bfqd_reset_in_service(bfqd);
|
|
}
|
|
|
|
/**
|
|
* __bfq_bfqq_recalc_budget - try to adapt the budget to the @bfqq behavior.
|
|
* @bfqd: device data.
|
|
* @bfqq: queue to update.
|
|
* @reason: reason for expiration.
|
|
*
|
|
* Handle the feedback on @bfqq budget at queue expiration.
|
|
* See the body for detailed comments.
|
|
*/
|
|
static void __bfq_bfqq_recalc_budget(struct bfq_data *bfqd,
|
|
struct bfq_queue *bfqq,
|
|
enum bfqq_expiration reason)
|
|
{
|
|
struct request *next_rq;
|
|
int budget, min_budget;
|
|
|
|
min_budget = bfq_min_budget(bfqd);
|
|
|
|
if (bfqq->wr_coeff == 1)
|
|
budget = bfqq->max_budget;
|
|
else /*
|
|
* Use a constant, low budget for weight-raised queues,
|
|
* to help achieve a low latency. Keep it slightly higher
|
|
* than the minimum possible budget, to cause a little
|
|
* bit fewer expirations.
|
|
*/
|
|
budget = 2 * min_budget;
|
|
|
|
bfq_log_bfqq(bfqd, bfqq, "recalc_budg: last budg %d, budg left %d",
|
|
bfqq->entity.budget, bfq_bfqq_budget_left(bfqq));
|
|
bfq_log_bfqq(bfqd, bfqq, "recalc_budg: last max_budg %d, min budg %d",
|
|
budget, bfq_min_budget(bfqd));
|
|
bfq_log_bfqq(bfqd, bfqq, "recalc_budg: sync %d, seeky %d",
|
|
bfq_bfqq_sync(bfqq), BFQQ_SEEKY(bfqd->in_service_queue));
|
|
|
|
if (bfq_bfqq_sync(bfqq) && bfqq->wr_coeff == 1) {
|
|
switch (reason) {
|
|
/*
|
|
* Caveat: in all the following cases we trade latency
|
|
* for throughput.
|
|
*/
|
|
case BFQQE_TOO_IDLE:
|
|
/*
|
|
* This is the only case where we may reduce
|
|
* the budget: if there is no request of the
|
|
* process still waiting for completion, then
|
|
* we assume (tentatively) that the timer has
|
|
* expired because the batch of requests of
|
|
* the process could have been served with a
|
|
* smaller budget. Hence, betting that
|
|
* process will behave in the same way when it
|
|
* becomes backlogged again, we reduce its
|
|
* next budget. As long as we guess right,
|
|
* this budget cut reduces the latency
|
|
* experienced by the process.
|
|
*
|
|
* However, if there are still outstanding
|
|
* requests, then the process may have not yet
|
|
* issued its next request just because it is
|
|
* still waiting for the completion of some of
|
|
* the still outstanding ones. So in this
|
|
* subcase we do not reduce its budget, on the
|
|
* contrary we increase it to possibly boost
|
|
* the throughput, as discussed in the
|
|
* comments to the BUDGET_TIMEOUT case.
|
|
*/
|
|
if (bfqq->dispatched > 0) /* still outstanding reqs */
|
|
budget = min(budget * 2, bfqd->bfq_max_budget);
|
|
else {
|
|
if (budget > 5 * min_budget)
|
|
budget -= 4 * min_budget;
|
|
else
|
|
budget = min_budget;
|
|
}
|
|
break;
|
|
case BFQQE_BUDGET_TIMEOUT:
|
|
/*
|
|
* We double the budget here because it gives
|
|
* the chance to boost the throughput if this
|
|
* is not a seeky process (and has bumped into
|
|
* this timeout because of, e.g., ZBR).
|
|
*/
|
|
budget = min(budget * 2, bfqd->bfq_max_budget);
|
|
break;
|
|
case BFQQE_BUDGET_EXHAUSTED:
|
|
/*
|
|
* The process still has backlog, and did not
|
|
* let either the budget timeout or the disk
|
|
* idling timeout expire. Hence it is not
|
|
* seeky, has a short thinktime and may be
|
|
* happy with a higher budget too. So
|
|
* definitely increase the budget of this good
|
|
* candidate to boost the disk throughput.
|
|
*/
|
|
budget = min(budget * 4, bfqd->bfq_max_budget);
|
|
break;
|
|
case BFQQE_NO_MORE_REQUESTS:
|
|
/*
|
|
* For queues that expire for this reason, it
|
|
* is particularly important to keep the
|
|
* budget close to the actual service they
|
|
* need. Doing so reduces the timestamp
|
|
* misalignment problem described in the
|
|
* comments in the body of
|
|
* __bfq_activate_entity. In fact, suppose
|
|
* that a queue systematically expires for
|
|
* BFQQE_NO_MORE_REQUESTS and presents a
|
|
* new request in time to enjoy timestamp
|
|
* back-shifting. The larger the budget of the
|
|
* queue is with respect to the service the
|
|
* queue actually requests in each service
|
|
* slot, the more times the queue can be
|
|
* reactivated with the same virtual finish
|
|
* time. It follows that, even if this finish
|
|
* time is pushed to the system virtual time
|
|
* to reduce the consequent timestamp
|
|
* misalignment, the queue unjustly enjoys for
|
|
* many re-activations a lower finish time
|
|
* than all newly activated queues.
|
|
*
|
|
* The service needed by bfqq is measured
|
|
* quite precisely by bfqq->entity.service.
|
|
* Since bfqq does not enjoy device idling,
|
|
* bfqq->entity.service is equal to the number
|
|
* of sectors that the process associated with
|
|
* bfqq requested to read/write before waiting
|
|
* for request completions, or blocking for
|
|
* other reasons.
|
|
*/
|
|
budget = max_t(int, bfqq->entity.service, min_budget);
|
|
break;
|
|
default:
|
|
return;
|
|
}
|
|
} else if (!bfq_bfqq_sync(bfqq)) {
|
|
/*
|
|
* Async queues get always the maximum possible
|
|
* budget, as for them we do not care about latency
|
|
* (in addition, their ability to dispatch is limited
|
|
* by the charging factor).
|
|
*/
|
|
budget = bfqd->bfq_max_budget;
|
|
}
|
|
|
|
bfqq->max_budget = budget;
|
|
|
|
if (bfqd->budgets_assigned >= bfq_stats_min_budgets &&
|
|
!bfqd->bfq_user_max_budget)
|
|
bfqq->max_budget = min(bfqq->max_budget, bfqd->bfq_max_budget);
|
|
|
|
/*
|
|
* If there is still backlog, then assign a new budget, making
|
|
* sure that it is large enough for the next request. Since
|
|
* the finish time of bfqq must be kept in sync with the
|
|
* budget, be sure to call __bfq_bfqq_expire() *after* this
|
|
* update.
|
|
*
|
|
* If there is no backlog, then no need to update the budget;
|
|
* it will be updated on the arrival of a new request.
|
|
*/
|
|
next_rq = bfqq->next_rq;
|
|
if (next_rq)
|
|
bfqq->entity.budget = max_t(unsigned long, bfqq->max_budget,
|
|
bfq_serv_to_charge(next_rq, bfqq));
|
|
|
|
bfq_log_bfqq(bfqd, bfqq, "head sect: %u, new budget %d",
|
|
next_rq ? blk_rq_sectors(next_rq) : 0,
|
|
bfqq->entity.budget);
|
|
}
|
|
|
|
/*
|
|
* Return true if the process associated with bfqq is "slow". The slow
|
|
* flag is used, in addition to the budget timeout, to reduce the
|
|
* amount of service provided to seeky processes, and thus reduce
|
|
* their chances to lower the throughput. More details in the comments
|
|
* on the function bfq_bfqq_expire().
|
|
*
|
|
* An important observation is in order: as discussed in the comments
|
|
* on the function bfq_update_peak_rate(), with devices with internal
|
|
* queues, it is hard if ever possible to know when and for how long
|
|
* an I/O request is processed by the device (apart from the trivial
|
|
* I/O pattern where a new request is dispatched only after the
|
|
* previous one has been completed). This makes it hard to evaluate
|
|
* the real rate at which the I/O requests of each bfq_queue are
|
|
* served. In fact, for an I/O scheduler like BFQ, serving a
|
|
* bfq_queue means just dispatching its requests during its service
|
|
* slot (i.e., until the budget of the queue is exhausted, or the
|
|
* queue remains idle, or, finally, a timeout fires). But, during the
|
|
* service slot of a bfq_queue, around 100 ms at most, the device may
|
|
* be even still processing requests of bfq_queues served in previous
|
|
* service slots. On the opposite end, the requests of the in-service
|
|
* bfq_queue may be completed after the service slot of the queue
|
|
* finishes.
|
|
*
|
|
* Anyway, unless more sophisticated solutions are used
|
|
* (where possible), the sum of the sizes of the requests dispatched
|
|
* during the service slot of a bfq_queue is probably the only
|
|
* approximation available for the service received by the bfq_queue
|
|
* during its service slot. And this sum is the quantity used in this
|
|
* function to evaluate the I/O speed of a process.
|
|
*/
|
|
static bool bfq_bfqq_is_slow(struct bfq_data *bfqd, struct bfq_queue *bfqq,
|
|
bool compensate, enum bfqq_expiration reason,
|
|
unsigned long *delta_ms)
|
|
{
|
|
ktime_t delta_ktime;
|
|
u32 delta_usecs;
|
|
bool slow = BFQQ_SEEKY(bfqq); /* if delta too short, use seekyness */
|
|
|
|
if (!bfq_bfqq_sync(bfqq))
|
|
return false;
|
|
|
|
if (compensate)
|
|
delta_ktime = bfqd->last_idling_start;
|
|
else
|
|
delta_ktime = ktime_get();
|
|
delta_ktime = ktime_sub(delta_ktime, bfqd->last_budget_start);
|
|
delta_usecs = ktime_to_us(delta_ktime);
|
|
|
|
/* don't use too short time intervals */
|
|
if (delta_usecs < 1000) {
|
|
if (blk_queue_nonrot(bfqd->queue))
|
|
/*
|
|
* give same worst-case guarantees as idling
|
|
* for seeky
|
|
*/
|
|
*delta_ms = BFQ_MIN_TT / NSEC_PER_MSEC;
|
|
else /* charge at least one seek */
|
|
*delta_ms = bfq_slice_idle / NSEC_PER_MSEC;
|
|
|
|
return slow;
|
|
}
|
|
|
|
*delta_ms = delta_usecs / USEC_PER_MSEC;
|
|
|
|
/*
|
|
* Use only long (> 20ms) intervals to filter out excessive
|
|
* spikes in service rate estimation.
|
|
*/
|
|
if (delta_usecs > 20000) {
|
|
/*
|
|
* Caveat for rotational devices: processes doing I/O
|
|
* in the slower disk zones tend to be slow(er) even
|
|
* if not seeky. In this respect, the estimated peak
|
|
* rate is likely to be an average over the disk
|
|
* surface. Accordingly, to not be too harsh with
|
|
* unlucky processes, a process is deemed slow only if
|
|
* its rate has been lower than half of the estimated
|
|
* peak rate.
|
|
*/
|
|
slow = bfqq->entity.service < bfqd->bfq_max_budget / 2;
|
|
}
|
|
|
|
bfq_log_bfqq(bfqd, bfqq, "bfq_bfqq_is_slow: slow %d", slow);
|
|
|
|
return slow;
|
|
}
|
|
|
|
/*
|
|
* To be deemed as soft real-time, an application must meet two
|
|
* requirements. First, the application must not require an average
|
|
* bandwidth higher than the approximate bandwidth required to playback or
|
|
* record a compressed high-definition video.
|
|
* The next function is invoked on the completion of the last request of a
|
|
* batch, to compute the next-start time instant, soft_rt_next_start, such
|
|
* that, if the next request of the application does not arrive before
|
|
* soft_rt_next_start, then the above requirement on the bandwidth is met.
|
|
*
|
|
* The second requirement is that the request pattern of the application is
|
|
* isochronous, i.e., that, after issuing a request or a batch of requests,
|
|
* the application stops issuing new requests until all its pending requests
|
|
* have been completed. After that, the application may issue a new batch,
|
|
* and so on.
|
|
* For this reason the next function is invoked to compute
|
|
* soft_rt_next_start only for applications that meet this requirement,
|
|
* whereas soft_rt_next_start is set to infinity for applications that do
|
|
* not.
|
|
*
|
|
* Unfortunately, even a greedy application may happen to behave in an
|
|
* isochronous way if the CPU load is high. In fact, the application may
|
|
* stop issuing requests while the CPUs are busy serving other processes,
|
|
* then restart, then stop again for a while, and so on. In addition, if
|
|
* the disk achieves a low enough throughput with the request pattern
|
|
* issued by the application (e.g., because the request pattern is random
|
|
* and/or the device is slow), then the application may meet the above
|
|
* bandwidth requirement too. To prevent such a greedy application to be
|
|
* deemed as soft real-time, a further rule is used in the computation of
|
|
* soft_rt_next_start: soft_rt_next_start must be higher than the current
|
|
* time plus the maximum time for which the arrival of a request is waited
|
|
* for when a sync queue becomes idle, namely bfqd->bfq_slice_idle.
|
|
* This filters out greedy applications, as the latter issue instead their
|
|
* next request as soon as possible after the last one has been completed
|
|
* (in contrast, when a batch of requests is completed, a soft real-time
|
|
* application spends some time processing data).
|
|
*
|
|
* Unfortunately, the last filter may easily generate false positives if
|
|
* only bfqd->bfq_slice_idle is used as a reference time interval and one
|
|
* or both the following cases occur:
|
|
* 1) HZ is so low that the duration of a jiffy is comparable to or higher
|
|
* than bfqd->bfq_slice_idle. This happens, e.g., on slow devices with
|
|
* HZ=100.
|
|
* 2) jiffies, instead of increasing at a constant rate, may stop increasing
|
|
* for a while, then suddenly 'jump' by several units to recover the lost
|
|
* increments. This seems to happen, e.g., inside virtual machines.
|
|
* To address this issue, we do not use as a reference time interval just
|
|
* bfqd->bfq_slice_idle, but bfqd->bfq_slice_idle plus a few jiffies. In
|
|
* particular we add the minimum number of jiffies for which the filter
|
|
* seems to be quite precise also in embedded systems and KVM/QEMU virtual
|
|
* machines.
|
|
*/
|
|
static unsigned long bfq_bfqq_softrt_next_start(struct bfq_data *bfqd,
|
|
struct bfq_queue *bfqq)
|
|
{
|
|
return max(bfqq->last_idle_bklogged +
|
|
HZ * bfqq->service_from_backlogged /
|
|
bfqd->bfq_wr_max_softrt_rate,
|
|
jiffies + nsecs_to_jiffies(bfqq->bfqd->bfq_slice_idle) + 4);
|
|
}
|
|
|
|
/*
|
|
* Return the farthest future time instant according to jiffies
|
|
* macros.
|
|
*/
|
|
static unsigned long bfq_greatest_from_now(void)
|
|
{
|
|
return jiffies + MAX_JIFFY_OFFSET;
|
|
}
|
|
|
|
/*
|
|
* Return the farthest past time instant according to jiffies
|
|
* macros.
|
|
*/
|
|
static unsigned long bfq_smallest_from_now(void)
|
|
{
|
|
return jiffies - MAX_JIFFY_OFFSET;
|
|
}
|
|
|
|
/**
|
|
* bfq_bfqq_expire - expire a queue.
|
|
* @bfqd: device owning the queue.
|
|
* @bfqq: the queue to expire.
|
|
* @compensate: if true, compensate for the time spent idling.
|
|
* @reason: the reason causing the expiration.
|
|
*
|
|
* If the process associated with bfqq does slow I/O (e.g., because it
|
|
* issues random requests), we charge bfqq with the time it has been
|
|
* in service instead of the service it has received (see
|
|
* bfq_bfqq_charge_time for details on how this goal is achieved). As
|
|
* a consequence, bfqq will typically get higher timestamps upon
|
|
* reactivation, and hence it will be rescheduled as if it had
|
|
* received more service than what it has actually received. In the
|
|
* end, bfqq receives less service in proportion to how slowly its
|
|
* associated process consumes its budgets (and hence how seriously it
|
|
* tends to lower the throughput). In addition, this time-charging
|
|
* strategy guarantees time fairness among slow processes. In
|
|
* contrast, if the process associated with bfqq is not slow, we
|
|
* charge bfqq exactly with the service it has received.
|
|
*
|
|
* Charging time to the first type of queues and the exact service to
|
|
* the other has the effect of using the WF2Q+ policy to schedule the
|
|
* former on a timeslice basis, without violating service domain
|
|
* guarantees among the latter.
|
|
*/
|
|
void bfq_bfqq_expire(struct bfq_data *bfqd,
|
|
struct bfq_queue *bfqq,
|
|
bool compensate,
|
|
enum bfqq_expiration reason)
|
|
{
|
|
bool slow;
|
|
unsigned long delta = 0;
|
|
struct bfq_entity *entity = &bfqq->entity;
|
|
int ref;
|
|
|
|
/*
|
|
* Check whether the process is slow (see bfq_bfqq_is_slow).
|
|
*/
|
|
slow = bfq_bfqq_is_slow(bfqd, bfqq, compensate, reason, &delta);
|
|
|
|
/*
|
|
* Increase service_from_backlogged before next statement,
|
|
* because the possible next invocation of
|
|
* bfq_bfqq_charge_time would likely inflate
|
|
* entity->service. In contrast, service_from_backlogged must
|
|
* contain real service, to enable the soft real-time
|
|
* heuristic to correctly compute the bandwidth consumed by
|
|
* bfqq.
|
|
*/
|
|
bfqq->service_from_backlogged += entity->service;
|
|
|
|
/*
|
|
* As above explained, charge slow (typically seeky) and
|
|
* timed-out queues with the time and not the service
|
|
* received, to favor sequential workloads.
|
|
*
|
|
* Processes doing I/O in the slower disk zones will tend to
|
|
* be slow(er) even if not seeky. Therefore, since the
|
|
* estimated peak rate is actually an average over the disk
|
|
* surface, these processes may timeout just for bad luck. To
|
|
* avoid punishing them, do not charge time to processes that
|
|
* succeeded in consuming at least 2/3 of their budget. This
|
|
* allows BFQ to preserve enough elasticity to still perform
|
|
* bandwidth, and not time, distribution with little unlucky
|
|
* or quasi-sequential processes.
|
|
*/
|
|
if (bfqq->wr_coeff == 1 &&
|
|
(slow ||
|
|
(reason == BFQQE_BUDGET_TIMEOUT &&
|
|
bfq_bfqq_budget_left(bfqq) >= entity->budget / 3)))
|
|
bfq_bfqq_charge_time(bfqd, bfqq, delta);
|
|
|
|
if (reason == BFQQE_TOO_IDLE &&
|
|
entity->service <= 2 * entity->budget / 10)
|
|
bfq_clear_bfqq_IO_bound(bfqq);
|
|
|
|
if (bfqd->low_latency && bfqq->wr_coeff == 1)
|
|
bfqq->last_wr_start_finish = jiffies;
|
|
|
|
if (bfqd->low_latency && bfqd->bfq_wr_max_softrt_rate > 0 &&
|
|
RB_EMPTY_ROOT(&bfqq->sort_list)) {
|
|
/*
|
|
* If we get here, and there are no outstanding
|
|
* requests, then the request pattern is isochronous
|
|
* (see the comments on the function
|
|
* bfq_bfqq_softrt_next_start()). Thus we can compute
|
|
* soft_rt_next_start. If, instead, the queue still
|
|
* has outstanding requests, then we have to wait for
|
|
* the completion of all the outstanding requests to
|
|
* discover whether the request pattern is actually
|
|
* isochronous.
|
|
*/
|
|
if (bfqq->dispatched == 0)
|
|
bfqq->soft_rt_next_start =
|
|
bfq_bfqq_softrt_next_start(bfqd, bfqq);
|
|
else {
|
|
/*
|
|
* The application is still waiting for the
|
|
* completion of one or more requests:
|
|
* prevent it from possibly being incorrectly
|
|
* deemed as soft real-time by setting its
|
|
* soft_rt_next_start to infinity. In fact,
|
|
* without this assignment, the application
|
|
* would be incorrectly deemed as soft
|
|
* real-time if:
|
|
* 1) it issued a new request before the
|
|
* completion of all its in-flight
|
|
* requests, and
|
|
* 2) at that time, its soft_rt_next_start
|
|
* happened to be in the past.
|
|
*/
|
|
bfqq->soft_rt_next_start =
|
|
bfq_greatest_from_now();
|
|
/*
|
|
* Schedule an update of soft_rt_next_start to when
|
|
* the task may be discovered to be isochronous.
|
|
*/
|
|
bfq_mark_bfqq_softrt_update(bfqq);
|
|
}
|
|
}
|
|
|
|
bfq_log_bfqq(bfqd, bfqq,
|
|
"expire (%d, slow %d, num_disp %d, idle_win %d)", reason,
|
|
slow, bfqq->dispatched, bfq_bfqq_idle_window(bfqq));
|
|
|
|
/*
|
|
* Increase, decrease or leave budget unchanged according to
|
|
* reason.
|
|
*/
|
|
__bfq_bfqq_recalc_budget(bfqd, bfqq, reason);
|
|
ref = bfqq->ref;
|
|
__bfq_bfqq_expire(bfqd, bfqq);
|
|
|
|
/* mark bfqq as waiting a request only if a bic still points to it */
|
|
if (ref > 1 && !bfq_bfqq_busy(bfqq) &&
|
|
reason != BFQQE_BUDGET_TIMEOUT &&
|
|
reason != BFQQE_BUDGET_EXHAUSTED)
|
|
bfq_mark_bfqq_non_blocking_wait_rq(bfqq);
|
|
}
|
|
|
|
/*
|
|
* Budget timeout is not implemented through a dedicated timer, but
|
|
* just checked on request arrivals and completions, as well as on
|
|
* idle timer expirations.
|
|
*/
|
|
static bool bfq_bfqq_budget_timeout(struct bfq_queue *bfqq)
|
|
{
|
|
return time_is_before_eq_jiffies(bfqq->budget_timeout);
|
|
}
|
|
|
|
/*
|
|
* If we expire a queue that is actively waiting (i.e., with the
|
|
* device idled) for the arrival of a new request, then we may incur
|
|
* the timestamp misalignment problem described in the body of the
|
|
* function __bfq_activate_entity. Hence we return true only if this
|
|
* condition does not hold, or if the queue is slow enough to deserve
|
|
* only to be kicked off for preserving a high throughput.
|
|
*/
|
|
static bool bfq_may_expire_for_budg_timeout(struct bfq_queue *bfqq)
|
|
{
|
|
bfq_log_bfqq(bfqq->bfqd, bfqq,
|
|
"may_budget_timeout: wait_request %d left %d timeout %d",
|
|
bfq_bfqq_wait_request(bfqq),
|
|
bfq_bfqq_budget_left(bfqq) >= bfqq->entity.budget / 3,
|
|
bfq_bfqq_budget_timeout(bfqq));
|
|
|
|
return (!bfq_bfqq_wait_request(bfqq) ||
|
|
bfq_bfqq_budget_left(bfqq) >= bfqq->entity.budget / 3)
|
|
&&
|
|
bfq_bfqq_budget_timeout(bfqq);
|
|
}
|
|
|
|
/*
|
|
* For a queue that becomes empty, device idling is allowed only if
|
|
* this function returns true for the queue. As a consequence, since
|
|
* device idling plays a critical role in both throughput boosting and
|
|
* service guarantees, the return value of this function plays a
|
|
* critical role in both these aspects as well.
|
|
*
|
|
* In a nutshell, this function returns true only if idling is
|
|
* beneficial for throughput or, even if detrimental for throughput,
|
|
* idling is however necessary to preserve service guarantees (low
|
|
* latency, desired throughput distribution, ...). In particular, on
|
|
* NCQ-capable devices, this function tries to return false, so as to
|
|
* help keep the drives' internal queues full, whenever this helps the
|
|
* device boost the throughput without causing any service-guarantee
|
|
* issue.
|
|
*
|
|
* In more detail, the return value of this function is obtained by,
|
|
* first, computing a number of boolean variables that take into
|
|
* account throughput and service-guarantee issues, and, then,
|
|
* combining these variables in a logical expression. Most of the
|
|
* issues taken into account are not trivial. We discuss these issues
|
|
* individually while introducing the variables.
|
|
*/
|
|
static bool bfq_bfqq_may_idle(struct bfq_queue *bfqq)
|
|
{
|
|
struct bfq_data *bfqd = bfqq->bfqd;
|
|
bool idling_boosts_thr, idling_boosts_thr_without_issues,
|
|
idling_needed_for_service_guarantees,
|
|
asymmetric_scenario;
|
|
|
|
if (bfqd->strict_guarantees)
|
|
return true;
|
|
|
|
/*
|
|
* The next variable takes into account the cases where idling
|
|
* boosts the throughput.
|
|
*
|
|
* The value of the variable is computed considering, first, that
|
|
* idling is virtually always beneficial for the throughput if:
|
|
* (a) the device is not NCQ-capable, or
|
|
* (b) regardless of the presence of NCQ, the device is rotational
|
|
* and the request pattern for bfqq is I/O-bound and sequential.
|
|
*
|
|
* Secondly, and in contrast to the above item (b), idling an
|
|
* NCQ-capable flash-based device would not boost the
|
|
* throughput even with sequential I/O; rather it would lower
|
|
* the throughput in proportion to how fast the device
|
|
* is. Accordingly, the next variable is true if any of the
|
|
* above conditions (a) and (b) is true, and, in particular,
|
|
* happens to be false if bfqd is an NCQ-capable flash-based
|
|
* device.
|
|
*/
|
|
idling_boosts_thr = !bfqd->hw_tag ||
|
|
(!blk_queue_nonrot(bfqd->queue) && bfq_bfqq_IO_bound(bfqq) &&
|
|
bfq_bfqq_idle_window(bfqq));
|
|
|
|
/*
|
|
* The value of the next variable,
|
|
* idling_boosts_thr_without_issues, is equal to that of
|
|
* idling_boosts_thr, unless a special case holds. In this
|
|
* special case, described below, idling may cause problems to
|
|
* weight-raised queues.
|
|
*
|
|
* When the request pool is saturated (e.g., in the presence
|
|
* of write hogs), if the processes associated with
|
|
* non-weight-raised queues ask for requests at a lower rate,
|
|
* then processes associated with weight-raised queues have a
|
|
* higher probability to get a request from the pool
|
|
* immediately (or at least soon) when they need one. Thus
|
|
* they have a higher probability to actually get a fraction
|
|
* of the device throughput proportional to their high
|
|
* weight. This is especially true with NCQ-capable drives,
|
|
* which enqueue several requests in advance, and further
|
|
* reorder internally-queued requests.
|
|
*
|
|
* For this reason, we force to false the value of
|
|
* idling_boosts_thr_without_issues if there are weight-raised
|
|
* busy queues. In this case, and if bfqq is not weight-raised,
|
|
* this guarantees that the device is not idled for bfqq (if,
|
|
* instead, bfqq is weight-raised, then idling will be
|
|
* guaranteed by another variable, see below). Combined with
|
|
* the timestamping rules of BFQ (see [1] for details), this
|
|
* behavior causes bfqq, and hence any sync non-weight-raised
|
|
* queue, to get a lower number of requests served, and thus
|
|
* to ask for a lower number of requests from the request
|
|
* pool, before the busy weight-raised queues get served
|
|
* again. This often mitigates starvation problems in the
|
|
* presence of heavy write workloads and NCQ, thereby
|
|
* guaranteeing a higher application and system responsiveness
|
|
* in these hostile scenarios.
|
|
*/
|
|
idling_boosts_thr_without_issues = idling_boosts_thr &&
|
|
bfqd->wr_busy_queues == 0;
|
|
|
|
/*
|
|
* There is then a case where idling must be performed not
|
|
* for throughput concerns, but to preserve service
|
|
* guarantees.
|
|
*
|
|
* To introduce this case, we can note that allowing the drive
|
|
* to enqueue more than one request at a time, and hence
|
|
* delegating de facto final scheduling decisions to the
|
|
* drive's internal scheduler, entails loss of control on the
|
|
* actual request service order. In particular, the critical
|
|
* situation is when requests from different processes happen
|
|
* to be present, at the same time, in the internal queue(s)
|
|
* of the drive. In such a situation, the drive, by deciding
|
|
* the service order of the internally-queued requests, does
|
|
* determine also the actual throughput distribution among
|
|
* these processes. But the drive typically has no notion or
|
|
* concern about per-process throughput distribution, and
|
|
* makes its decisions only on a per-request basis. Therefore,
|
|
* the service distribution enforced by the drive's internal
|
|
* scheduler is likely to coincide with the desired
|
|
* device-throughput distribution only in a completely
|
|
* symmetric scenario where:
|
|
* (i) each of these processes must get the same throughput as
|
|
* the others;
|
|
* (ii) all these processes have the same I/O pattern
|
|
(either sequential or random).
|
|
* In fact, in such a scenario, the drive will tend to treat
|
|
* the requests of each of these processes in about the same
|
|
* way as the requests of the others, and thus to provide
|
|
* each of these processes with about the same throughput
|
|
* (which is exactly the desired throughput distribution). In
|
|
* contrast, in any asymmetric scenario, device idling is
|
|
* certainly needed to guarantee that bfqq receives its
|
|
* assigned fraction of the device throughput (see [1] for
|
|
* details).
|
|
*
|
|
* We address this issue by controlling, actually, only the
|
|
* symmetry sub-condition (i), i.e., provided that
|
|
* sub-condition (i) holds, idling is not performed,
|
|
* regardless of whether sub-condition (ii) holds. In other
|
|
* words, only if sub-condition (i) holds, then idling is
|
|
* allowed, and the device tends to be prevented from queueing
|
|
* many requests, possibly of several processes. The reason
|
|
* for not controlling also sub-condition (ii) is that we
|
|
* exploit preemption to preserve guarantees in case of
|
|
* symmetric scenarios, even if (ii) does not hold, as
|
|
* explained in the next two paragraphs.
|
|
*
|
|
* Even if a queue, say Q, is expired when it remains idle, Q
|
|
* can still preempt the new in-service queue if the next
|
|
* request of Q arrives soon (see the comments on
|
|
* bfq_bfqq_update_budg_for_activation). If all queues and
|
|
* groups have the same weight, this form of preemption,
|
|
* combined with the hole-recovery heuristic described in the
|
|
* comments on function bfq_bfqq_update_budg_for_activation,
|
|
* are enough to preserve a correct bandwidth distribution in
|
|
* the mid term, even without idling. In fact, even if not
|
|
* idling allows the internal queues of the device to contain
|
|
* many requests, and thus to reorder requests, we can rather
|
|
* safely assume that the internal scheduler still preserves a
|
|
* minimum of mid-term fairness. The motivation for using
|
|
* preemption instead of idling is that, by not idling,
|
|
* service guarantees are preserved without minimally
|
|
* sacrificing throughput. In other words, both a high
|
|
* throughput and its desired distribution are obtained.
|
|
*
|
|
* More precisely, this preemption-based, idleless approach
|
|
* provides fairness in terms of IOPS, and not sectors per
|
|
* second. This can be seen with a simple example. Suppose
|
|
* that there are two queues with the same weight, but that
|
|
* the first queue receives requests of 8 sectors, while the
|
|
* second queue receives requests of 1024 sectors. In
|
|
* addition, suppose that each of the two queues contains at
|
|
* most one request at a time, which implies that each queue
|
|
* always remains idle after it is served. Finally, after
|
|
* remaining idle, each queue receives very quickly a new
|
|
* request. It follows that the two queues are served
|
|
* alternatively, preempting each other if needed. This
|
|
* implies that, although both queues have the same weight,
|
|
* the queue with large requests receives a service that is
|
|
* 1024/8 times as high as the service received by the other
|
|
* queue.
|
|
*
|
|
* On the other hand, device idling is performed, and thus
|
|
* pure sector-domain guarantees are provided, for the
|
|
* following queues, which are likely to need stronger
|
|
* throughput guarantees: weight-raised queues, and queues
|
|
* with a higher weight than other queues. When such queues
|
|
* are active, sub-condition (i) is false, which triggers
|
|
* device idling.
|
|
*
|
|
* According to the above considerations, the next variable is
|
|
* true (only) if sub-condition (i) holds. To compute the
|
|
* value of this variable, we not only use the return value of
|
|
* the function bfq_symmetric_scenario(), but also check
|
|
* whether bfqq is being weight-raised, because
|
|
* bfq_symmetric_scenario() does not take into account also
|
|
* weight-raised queues (see comments on
|
|
* bfq_weights_tree_add()).
|
|
*
|
|
* As a side note, it is worth considering that the above
|
|
* device-idling countermeasures may however fail in the
|
|
* following unlucky scenario: if idling is (correctly)
|
|
* disabled in a time period during which all symmetry
|
|
* sub-conditions hold, and hence the device is allowed to
|
|
* enqueue many requests, but at some later point in time some
|
|
* sub-condition stops to hold, then it may become impossible
|
|
* to let requests be served in the desired order until all
|
|
* the requests already queued in the device have been served.
|
|
*/
|
|
asymmetric_scenario = bfqq->wr_coeff > 1 ||
|
|
!bfq_symmetric_scenario(bfqd);
|
|
|
|
/*
|
|
* Finally, there is a case where maximizing throughput is the
|
|
* best choice even if it may cause unfairness toward
|
|
* bfqq. Such a case is when bfqq became active in a burst of
|
|
* queue activations. Queues that became active during a large
|
|
* burst benefit only from throughput, as discussed in the
|
|
* comments on bfq_handle_burst. Thus, if bfqq became active
|
|
* in a burst and not idling the device maximizes throughput,
|
|
* then the device must no be idled, because not idling the
|
|
* device provides bfqq and all other queues in the burst with
|
|
* maximum benefit. Combining this and the above case, we can
|
|
* now establish when idling is actually needed to preserve
|
|
* service guarantees.
|
|
*/
|
|
idling_needed_for_service_guarantees =
|
|
asymmetric_scenario && !bfq_bfqq_in_large_burst(bfqq);
|
|
|
|
/*
|
|
* We have now all the components we need to compute the return
|
|
* value of the function, which is true only if both the following
|
|
* conditions hold:
|
|
* 1) bfqq is sync, because idling make sense only for sync queues;
|
|
* 2) idling either boosts the throughput (without issues), or
|
|
* is necessary to preserve service guarantees.
|
|
*/
|
|
return bfq_bfqq_sync(bfqq) &&
|
|
(idling_boosts_thr_without_issues ||
|
|
idling_needed_for_service_guarantees);
|
|
}
|
|
|
|
/*
|
|
* If the in-service queue is empty but the function bfq_bfqq_may_idle
|
|
* returns true, then:
|
|
* 1) the queue must remain in service and cannot be expired, and
|
|
* 2) the device must be idled to wait for the possible arrival of a new
|
|
* request for the queue.
|
|
* See the comments on the function bfq_bfqq_may_idle for the reasons
|
|
* why performing device idling is the best choice to boost the throughput
|
|
* and preserve service guarantees when bfq_bfqq_may_idle itself
|
|
* returns true.
|
|
*/
|
|
static bool bfq_bfqq_must_idle(struct bfq_queue *bfqq)
|
|
{
|
|
struct bfq_data *bfqd = bfqq->bfqd;
|
|
|
|
return RB_EMPTY_ROOT(&bfqq->sort_list) && bfqd->bfq_slice_idle != 0 &&
|
|
bfq_bfqq_may_idle(bfqq);
|
|
}
|
|
|
|
/*
|
|
* Select a queue for service. If we have a current queue in service,
|
|
* check whether to continue servicing it, or retrieve and set a new one.
|
|
*/
|
|
static struct bfq_queue *bfq_select_queue(struct bfq_data *bfqd)
|
|
{
|
|
struct bfq_queue *bfqq;
|
|
struct request *next_rq;
|
|
enum bfqq_expiration reason = BFQQE_BUDGET_TIMEOUT;
|
|
|
|
bfqq = bfqd->in_service_queue;
|
|
if (!bfqq)
|
|
goto new_queue;
|
|
|
|
bfq_log_bfqq(bfqd, bfqq, "select_queue: already in-service queue");
|
|
|
|
if (bfq_may_expire_for_budg_timeout(bfqq) &&
|
|
!bfq_bfqq_wait_request(bfqq) &&
|
|
!bfq_bfqq_must_idle(bfqq))
|
|
goto expire;
|
|
|
|
check_queue:
|
|
/*
|
|
* This loop is rarely executed more than once. Even when it
|
|
* happens, it is much more convenient to re-execute this loop
|
|
* than to return NULL and trigger a new dispatch to get a
|
|
* request served.
|
|
*/
|
|
next_rq = bfqq->next_rq;
|
|
/*
|
|
* If bfqq has requests queued and it has enough budget left to
|
|
* serve them, keep the queue, otherwise expire it.
|
|
*/
|
|
if (next_rq) {
|
|
if (bfq_serv_to_charge(next_rq, bfqq) >
|
|
bfq_bfqq_budget_left(bfqq)) {
|
|
/*
|
|
* Expire the queue for budget exhaustion,
|
|
* which makes sure that the next budget is
|
|
* enough to serve the next request, even if
|
|
* it comes from the fifo expired path.
|
|
*/
|
|
reason = BFQQE_BUDGET_EXHAUSTED;
|
|
goto expire;
|
|
} else {
|
|
/*
|
|
* The idle timer may be pending because we may
|
|
* not disable disk idling even when a new request
|
|
* arrives.
|
|
*/
|
|
if (bfq_bfqq_wait_request(bfqq)) {
|
|
/*
|
|
* If we get here: 1) at least a new request
|
|
* has arrived but we have not disabled the
|
|
* timer because the request was too small,
|
|
* 2) then the block layer has unplugged
|
|
* the device, causing the dispatch to be
|
|
* invoked.
|
|
*
|
|
* Since the device is unplugged, now the
|
|
* requests are probably large enough to
|
|
* provide a reasonable throughput.
|
|
* So we disable idling.
|
|
*/
|
|
bfq_clear_bfqq_wait_request(bfqq);
|
|
hrtimer_try_to_cancel(&bfqd->idle_slice_timer);
|
|
bfqg_stats_update_idle_time(bfqq_group(bfqq));
|
|
}
|
|
goto keep_queue;
|
|
}
|
|
}
|
|
|
|
/*
|
|
* No requests pending. However, if the in-service queue is idling
|
|
* for a new request, or has requests waiting for a completion and
|
|
* may idle after their completion, then keep it anyway.
|
|
*/
|
|
if (bfq_bfqq_wait_request(bfqq) ||
|
|
(bfqq->dispatched != 0 && bfq_bfqq_may_idle(bfqq))) {
|
|
bfqq = NULL;
|
|
goto keep_queue;
|
|
}
|
|
|
|
reason = BFQQE_NO_MORE_REQUESTS;
|
|
expire:
|
|
bfq_bfqq_expire(bfqd, bfqq, false, reason);
|
|
new_queue:
|
|
bfqq = bfq_set_in_service_queue(bfqd);
|
|
if (bfqq) {
|
|
bfq_log_bfqq(bfqd, bfqq, "select_queue: checking new queue");
|
|
goto check_queue;
|
|
}
|
|
keep_queue:
|
|
if (bfqq)
|
|
bfq_log_bfqq(bfqd, bfqq, "select_queue: returned this queue");
|
|
else
|
|
bfq_log(bfqd, "select_queue: no queue returned");
|
|
|
|
return bfqq;
|
|
}
|
|
|
|
static void bfq_update_wr_data(struct bfq_data *bfqd, struct bfq_queue *bfqq)
|
|
{
|
|
struct bfq_entity *entity = &bfqq->entity;
|
|
|
|
if (bfqq->wr_coeff > 1) { /* queue is being weight-raised */
|
|
bfq_log_bfqq(bfqd, bfqq,
|
|
"raising period dur %u/%u msec, old coeff %u, w %d(%d)",
|
|
jiffies_to_msecs(jiffies - bfqq->last_wr_start_finish),
|
|
jiffies_to_msecs(bfqq->wr_cur_max_time),
|
|
bfqq->wr_coeff,
|
|
bfqq->entity.weight, bfqq->entity.orig_weight);
|
|
|
|
if (entity->prio_changed)
|
|
bfq_log_bfqq(bfqd, bfqq, "WARN: pending prio change");
|
|
|
|
/*
|
|
* If the queue was activated in a burst, or too much
|
|
* time has elapsed from the beginning of this
|
|
* weight-raising period, then end weight raising.
|
|
*/
|
|
if (bfq_bfqq_in_large_burst(bfqq))
|
|
bfq_bfqq_end_wr(bfqq);
|
|
else if (time_is_before_jiffies(bfqq->last_wr_start_finish +
|
|
bfqq->wr_cur_max_time)) {
|
|
if (bfqq->wr_cur_max_time != bfqd->bfq_wr_rt_max_time ||
|
|
time_is_before_jiffies(bfqq->wr_start_at_switch_to_srt +
|
|
bfq_wr_duration(bfqd)))
|
|
bfq_bfqq_end_wr(bfqq);
|
|
else {
|
|
/* switch back to interactive wr */
|
|
bfqq->wr_coeff = bfqd->bfq_wr_coeff;
|
|
bfqq->wr_cur_max_time = bfq_wr_duration(bfqd);
|
|
bfqq->last_wr_start_finish =
|
|
bfqq->wr_start_at_switch_to_srt;
|
|
bfqq->entity.prio_changed = 1;
|
|
}
|
|
}
|
|
}
|
|
/*
|
|
* To improve latency (for this or other queues), immediately
|
|
* update weight both if it must be raised and if it must be
|
|
* lowered. Since, entity may be on some active tree here, and
|
|
* might have a pending change of its ioprio class, invoke
|
|
* next function with the last parameter unset (see the
|
|
* comments on the function).
|
|
*/
|
|
if ((entity->weight > entity->orig_weight) != (bfqq->wr_coeff > 1))
|
|
__bfq_entity_update_weight_prio(bfq_entity_service_tree(entity),
|
|
entity, false);
|
|
}
|
|
|
|
/*
|
|
* Dispatch next request from bfqq.
|
|
*/
|
|
static struct request *bfq_dispatch_rq_from_bfqq(struct bfq_data *bfqd,
|
|
struct bfq_queue *bfqq)
|
|
{
|
|
struct request *rq = bfqq->next_rq;
|
|
unsigned long service_to_charge;
|
|
|
|
service_to_charge = bfq_serv_to_charge(rq, bfqq);
|
|
|
|
bfq_bfqq_served(bfqq, service_to_charge);
|
|
|
|
bfq_dispatch_remove(bfqd->queue, rq);
|
|
|
|
/*
|
|
* If weight raising has to terminate for bfqq, then next
|
|
* function causes an immediate update of bfqq's weight,
|
|
* without waiting for next activation. As a consequence, on
|
|
* expiration, bfqq will be timestamped as if has never been
|
|
* weight-raised during this service slot, even if it has
|
|
* received part or even most of the service as a
|
|
* weight-raised queue. This inflates bfqq's timestamps, which
|
|
* is beneficial, as bfqq is then more willing to leave the
|
|
* device immediately to possible other weight-raised queues.
|
|
*/
|
|
bfq_update_wr_data(bfqd, bfqq);
|
|
|
|
/*
|
|
* Expire bfqq, pretending that its budget expired, if bfqq
|
|
* belongs to CLASS_IDLE and other queues are waiting for
|
|
* service.
|
|
*/
|
|
if (bfqd->busy_queues > 1 && bfq_class_idle(bfqq))
|
|
goto expire;
|
|
|
|
return rq;
|
|
|
|
expire:
|
|
bfq_bfqq_expire(bfqd, bfqq, false, BFQQE_BUDGET_EXHAUSTED);
|
|
return rq;
|
|
}
|
|
|
|
static bool bfq_has_work(struct blk_mq_hw_ctx *hctx)
|
|
{
|
|
struct bfq_data *bfqd = hctx->queue->elevator->elevator_data;
|
|
|
|
/*
|
|
* Avoiding lock: a race on bfqd->busy_queues should cause at
|
|
* most a call to dispatch for nothing
|
|
*/
|
|
return !list_empty_careful(&bfqd->dispatch) ||
|
|
bfqd->busy_queues > 0;
|
|
}
|
|
|
|
static struct request *__bfq_dispatch_request(struct blk_mq_hw_ctx *hctx)
|
|
{
|
|
struct bfq_data *bfqd = hctx->queue->elevator->elevator_data;
|
|
struct request *rq = NULL;
|
|
struct bfq_queue *bfqq = NULL;
|
|
|
|
if (!list_empty(&bfqd->dispatch)) {
|
|
rq = list_first_entry(&bfqd->dispatch, struct request,
|
|
queuelist);
|
|
list_del_init(&rq->queuelist);
|
|
|
|
bfqq = RQ_BFQQ(rq);
|
|
|
|
if (bfqq) {
|
|
/*
|
|
* Increment counters here, because this
|
|
* dispatch does not follow the standard
|
|
* dispatch flow (where counters are
|
|
* incremented)
|
|
*/
|
|
bfqq->dispatched++;
|
|
|
|
goto inc_in_driver_start_rq;
|
|
}
|
|
|
|
/*
|
|
* We exploit the put_rq_private hook to decrement
|
|
* rq_in_driver, but put_rq_private will not be
|
|
* invoked on this request. So, to avoid unbalance,
|
|
* just start this request, without incrementing
|
|
* rq_in_driver. As a negative consequence,
|
|
* rq_in_driver is deceptively lower than it should be
|
|
* while this request is in service. This may cause
|
|
* bfq_schedule_dispatch to be invoked uselessly.
|
|
*
|
|
* As for implementing an exact solution, the
|
|
* put_request hook, if defined, is probably invoked
|
|
* also on this request. So, by exploiting this hook,
|
|
* we could 1) increment rq_in_driver here, and 2)
|
|
* decrement it in put_request. Such a solution would
|
|
* let the value of the counter be always accurate,
|
|
* but it would entail using an extra interface
|
|
* function. This cost seems higher than the benefit,
|
|
* being the frequency of non-elevator-private
|
|
* requests very low.
|
|
*/
|
|
goto start_rq;
|
|
}
|
|
|
|
bfq_log(bfqd, "dispatch requests: %d busy queues", bfqd->busy_queues);
|
|
|
|
if (bfqd->busy_queues == 0)
|
|
goto exit;
|
|
|
|
/*
|
|
* Force device to serve one request at a time if
|
|
* strict_guarantees is true. Forcing this service scheme is
|
|
* currently the ONLY way to guarantee that the request
|
|
* service order enforced by the scheduler is respected by a
|
|
* queueing device. Otherwise the device is free even to make
|
|
* some unlucky request wait for as long as the device
|
|
* wishes.
|
|
*
|
|
* Of course, serving one request at at time may cause loss of
|
|
* throughput.
|
|
*/
|
|
if (bfqd->strict_guarantees && bfqd->rq_in_driver > 0)
|
|
goto exit;
|
|
|
|
bfqq = bfq_select_queue(bfqd);
|
|
if (!bfqq)
|
|
goto exit;
|
|
|
|
rq = bfq_dispatch_rq_from_bfqq(bfqd, bfqq);
|
|
|
|
if (rq) {
|
|
inc_in_driver_start_rq:
|
|
bfqd->rq_in_driver++;
|
|
start_rq:
|
|
rq->rq_flags |= RQF_STARTED;
|
|
}
|
|
exit:
|
|
return rq;
|
|
}
|
|
|
|
static struct request *bfq_dispatch_request(struct blk_mq_hw_ctx *hctx)
|
|
{
|
|
struct bfq_data *bfqd = hctx->queue->elevator->elevator_data;
|
|
struct request *rq;
|
|
|
|
spin_lock_irq(&bfqd->lock);
|
|
|
|
rq = __bfq_dispatch_request(hctx);
|
|
spin_unlock_irq(&bfqd->lock);
|
|
|
|
return rq;
|
|
}
|
|
|
|
/*
|
|
* Task holds one reference to the queue, dropped when task exits. Each rq
|
|
* in-flight on this queue also holds a reference, dropped when rq is freed.
|
|
*
|
|
* Scheduler lock must be held here. Recall not to use bfqq after calling
|
|
* this function on it.
|
|
*/
|
|
void bfq_put_queue(struct bfq_queue *bfqq)
|
|
{
|
|
#ifdef CONFIG_BFQ_GROUP_IOSCHED
|
|
struct bfq_group *bfqg = bfqq_group(bfqq);
|
|
#endif
|
|
|
|
if (bfqq->bfqd)
|
|
bfq_log_bfqq(bfqq->bfqd, bfqq, "put_queue: %p %d",
|
|
bfqq, bfqq->ref);
|
|
|
|
bfqq->ref--;
|
|
if (bfqq->ref)
|
|
return;
|
|
|
|
if (bfq_bfqq_sync(bfqq))
|
|
/*
|
|
* The fact that this queue is being destroyed does not
|
|
* invalidate the fact that this queue may have been
|
|
* activated during the current burst. As a consequence,
|
|
* although the queue does not exist anymore, and hence
|
|
* needs to be removed from the burst list if there,
|
|
* the burst size has not to be decremented.
|
|
*/
|
|
hlist_del_init(&bfqq->burst_list_node);
|
|
|
|
kmem_cache_free(bfq_pool, bfqq);
|
|
#ifdef CONFIG_BFQ_GROUP_IOSCHED
|
|
bfqg_and_blkg_put(bfqg);
|
|
#endif
|
|
}
|
|
|
|
static void bfq_put_cooperator(struct bfq_queue *bfqq)
|
|
{
|
|
struct bfq_queue *__bfqq, *next;
|
|
|
|
/*
|
|
* If this queue was scheduled to merge with another queue, be
|
|
* sure to drop the reference taken on that queue (and others in
|
|
* the merge chain). See bfq_setup_merge and bfq_merge_bfqqs.
|
|
*/
|
|
__bfqq = bfqq->new_bfqq;
|
|
while (__bfqq) {
|
|
if (__bfqq == bfqq)
|
|
break;
|
|
next = __bfqq->new_bfqq;
|
|
bfq_put_queue(__bfqq);
|
|
__bfqq = next;
|
|
}
|
|
}
|
|
|
|
static void bfq_exit_bfqq(struct bfq_data *bfqd, struct bfq_queue *bfqq)
|
|
{
|
|
if (bfqq == bfqd->in_service_queue) {
|
|
__bfq_bfqq_expire(bfqd, bfqq);
|
|
bfq_schedule_dispatch(bfqd);
|
|
}
|
|
|
|
bfq_log_bfqq(bfqd, bfqq, "exit_bfqq: %p, %d", bfqq, bfqq->ref);
|
|
|
|
bfq_put_cooperator(bfqq);
|
|
|
|
bfq_put_queue(bfqq); /* release process reference */
|
|
}
|
|
|
|
static void bfq_exit_icq_bfqq(struct bfq_io_cq *bic, bool is_sync)
|
|
{
|
|
struct bfq_queue *bfqq = bic_to_bfqq(bic, is_sync);
|
|
struct bfq_data *bfqd;
|
|
|
|
if (bfqq)
|
|
bfqd = bfqq->bfqd; /* NULL if scheduler already exited */
|
|
|
|
if (bfqq && bfqd) {
|
|
unsigned long flags;
|
|
|
|
spin_lock_irqsave(&bfqd->lock, flags);
|
|
bfq_exit_bfqq(bfqd, bfqq);
|
|
bic_set_bfqq(bic, NULL, is_sync);
|
|
spin_unlock_irqrestore(&bfqd->lock, flags);
|
|
}
|
|
}
|
|
|
|
static void bfq_exit_icq(struct io_cq *icq)
|
|
{
|
|
struct bfq_io_cq *bic = icq_to_bic(icq);
|
|
|
|
bfq_exit_icq_bfqq(bic, true);
|
|
bfq_exit_icq_bfqq(bic, false);
|
|
}
|
|
|
|
/*
|
|
* Update the entity prio values; note that the new values will not
|
|
* be used until the next (re)activation.
|
|
*/
|
|
static void
|
|
bfq_set_next_ioprio_data(struct bfq_queue *bfqq, struct bfq_io_cq *bic)
|
|
{
|
|
struct task_struct *tsk = current;
|
|
int ioprio_class;
|
|
struct bfq_data *bfqd = bfqq->bfqd;
|
|
|
|
if (!bfqd)
|
|
return;
|
|
|
|
ioprio_class = IOPRIO_PRIO_CLASS(bic->ioprio);
|
|
switch (ioprio_class) {
|
|
default:
|
|
dev_err(bfqq->bfqd->queue->backing_dev_info->dev,
|
|
"bfq: bad prio class %d\n", ioprio_class);
|
|
case IOPRIO_CLASS_NONE:
|
|
/*
|
|
* No prio set, inherit CPU scheduling settings.
|
|
*/
|
|
bfqq->new_ioprio = task_nice_ioprio(tsk);
|
|
bfqq->new_ioprio_class = task_nice_ioclass(tsk);
|
|
break;
|
|
case IOPRIO_CLASS_RT:
|
|
bfqq->new_ioprio = IOPRIO_PRIO_DATA(bic->ioprio);
|
|
bfqq->new_ioprio_class = IOPRIO_CLASS_RT;
|
|
break;
|
|
case IOPRIO_CLASS_BE:
|
|
bfqq->new_ioprio = IOPRIO_PRIO_DATA(bic->ioprio);
|
|
bfqq->new_ioprio_class = IOPRIO_CLASS_BE;
|
|
break;
|
|
case IOPRIO_CLASS_IDLE:
|
|
bfqq->new_ioprio_class = IOPRIO_CLASS_IDLE;
|
|
bfqq->new_ioprio = 7;
|
|
bfq_clear_bfqq_idle_window(bfqq);
|
|
break;
|
|
}
|
|
|
|
if (bfqq->new_ioprio >= IOPRIO_BE_NR) {
|
|
pr_crit("bfq_set_next_ioprio_data: new_ioprio %d\n",
|
|
bfqq->new_ioprio);
|
|
bfqq->new_ioprio = IOPRIO_BE_NR;
|
|
}
|
|
|
|
bfqq->entity.new_weight = bfq_ioprio_to_weight(bfqq->new_ioprio);
|
|
bfqq->entity.prio_changed = 1;
|
|
}
|
|
|
|
static struct bfq_queue *bfq_get_queue(struct bfq_data *bfqd,
|
|
struct bio *bio, bool is_sync,
|
|
struct bfq_io_cq *bic);
|
|
|
|
static void bfq_check_ioprio_change(struct bfq_io_cq *bic, struct bio *bio)
|
|
{
|
|
struct bfq_data *bfqd = bic_to_bfqd(bic);
|
|
struct bfq_queue *bfqq;
|
|
int ioprio = bic->icq.ioc->ioprio;
|
|
|
|
/*
|
|
* This condition may trigger on a newly created bic, be sure to
|
|
* drop the lock before returning.
|
|
*/
|
|
if (unlikely(!bfqd) || likely(bic->ioprio == ioprio))
|
|
return;
|
|
|
|
bic->ioprio = ioprio;
|
|
|
|
bfqq = bic_to_bfqq(bic, false);
|
|
if (bfqq) {
|
|
/* release process reference on this queue */
|
|
bfq_put_queue(bfqq);
|
|
bfqq = bfq_get_queue(bfqd, bio, BLK_RW_ASYNC, bic);
|
|
bic_set_bfqq(bic, bfqq, false);
|
|
}
|
|
|
|
bfqq = bic_to_bfqq(bic, true);
|
|
if (bfqq)
|
|
bfq_set_next_ioprio_data(bfqq, bic);
|
|
}
|
|
|
|
static void bfq_init_bfqq(struct bfq_data *bfqd, struct bfq_queue *bfqq,
|
|
struct bfq_io_cq *bic, pid_t pid, int is_sync)
|
|
{
|
|
RB_CLEAR_NODE(&bfqq->entity.rb_node);
|
|
INIT_LIST_HEAD(&bfqq->fifo);
|
|
INIT_HLIST_NODE(&bfqq->burst_list_node);
|
|
|
|
bfqq->ref = 0;
|
|
bfqq->bfqd = bfqd;
|
|
|
|
if (bic)
|
|
bfq_set_next_ioprio_data(bfqq, bic);
|
|
|
|
if (is_sync) {
|
|
if (!bfq_class_idle(bfqq))
|
|
bfq_mark_bfqq_idle_window(bfqq);
|
|
bfq_mark_bfqq_sync(bfqq);
|
|
bfq_mark_bfqq_just_created(bfqq);
|
|
} else
|
|
bfq_clear_bfqq_sync(bfqq);
|
|
|
|
/* set end request to minus infinity from now */
|
|
bfqq->ttime.last_end_request = ktime_get_ns() + 1;
|
|
|
|
bfq_mark_bfqq_IO_bound(bfqq);
|
|
|
|
bfqq->pid = pid;
|
|
|
|
/* Tentative initial value to trade off between thr and lat */
|
|
bfqq->max_budget = (2 * bfq_max_budget(bfqd)) / 3;
|
|
bfqq->budget_timeout = bfq_smallest_from_now();
|
|
|
|
bfqq->wr_coeff = 1;
|
|
bfqq->last_wr_start_finish = jiffies;
|
|
bfqq->wr_start_at_switch_to_srt = bfq_smallest_from_now();
|
|
bfqq->split_time = bfq_smallest_from_now();
|
|
|
|
/*
|
|
* Set to the value for which bfqq will not be deemed as
|
|
* soft rt when it becomes backlogged.
|
|
*/
|
|
bfqq->soft_rt_next_start = bfq_greatest_from_now();
|
|
|
|
/* first request is almost certainly seeky */
|
|
bfqq->seek_history = 1;
|
|
}
|
|
|
|
static struct bfq_queue **bfq_async_queue_prio(struct bfq_data *bfqd,
|
|
struct bfq_group *bfqg,
|
|
int ioprio_class, int ioprio)
|
|
{
|
|
switch (ioprio_class) {
|
|
case IOPRIO_CLASS_RT:
|
|
return &bfqg->async_bfqq[0][ioprio];
|
|
case IOPRIO_CLASS_NONE:
|
|
ioprio = IOPRIO_NORM;
|
|
/* fall through */
|
|
case IOPRIO_CLASS_BE:
|
|
return &bfqg->async_bfqq[1][ioprio];
|
|
case IOPRIO_CLASS_IDLE:
|
|
return &bfqg->async_idle_bfqq;
|
|
default:
|
|
return NULL;
|
|
}
|
|
}
|
|
|
|
static struct bfq_queue *bfq_get_queue(struct bfq_data *bfqd,
|
|
struct bio *bio, bool is_sync,
|
|
struct bfq_io_cq *bic)
|
|
{
|
|
const int ioprio = IOPRIO_PRIO_DATA(bic->ioprio);
|
|
const int ioprio_class = IOPRIO_PRIO_CLASS(bic->ioprio);
|
|
struct bfq_queue **async_bfqq = NULL;
|
|
struct bfq_queue *bfqq;
|
|
struct bfq_group *bfqg;
|
|
|
|
rcu_read_lock();
|
|
|
|
bfqg = bfq_find_set_group(bfqd, bio_blkcg(bio));
|
|
if (!bfqg) {
|
|
bfqq = &bfqd->oom_bfqq;
|
|
goto out;
|
|
}
|
|
|
|
if (!is_sync) {
|
|
async_bfqq = bfq_async_queue_prio(bfqd, bfqg, ioprio_class,
|
|
ioprio);
|
|
bfqq = *async_bfqq;
|
|
if (bfqq)
|
|
goto out;
|
|
}
|
|
|
|
bfqq = kmem_cache_alloc_node(bfq_pool,
|
|
GFP_NOWAIT | __GFP_ZERO | __GFP_NOWARN,
|
|
bfqd->queue->node);
|
|
|
|
if (bfqq) {
|
|
bfq_init_bfqq(bfqd, bfqq, bic, current->pid,
|
|
is_sync);
|
|
bfq_init_entity(&bfqq->entity, bfqg);
|
|
bfq_log_bfqq(bfqd, bfqq, "allocated");
|
|
} else {
|
|
bfqq = &bfqd->oom_bfqq;
|
|
bfq_log_bfqq(bfqd, bfqq, "using oom bfqq");
|
|
goto out;
|
|
}
|
|
|
|
/*
|
|
* Pin the queue now that it's allocated, scheduler exit will
|
|
* prune it.
|
|
*/
|
|
if (async_bfqq) {
|
|
bfqq->ref++; /*
|
|
* Extra group reference, w.r.t. sync
|
|
* queue. This extra reference is removed
|
|
* only if bfqq->bfqg disappears, to
|
|
* guarantee that this queue is not freed
|
|
* until its group goes away.
|
|
*/
|
|
bfq_log_bfqq(bfqd, bfqq, "get_queue, bfqq not in async: %p, %d",
|
|
bfqq, bfqq->ref);
|
|
*async_bfqq = bfqq;
|
|
}
|
|
|
|
out:
|
|
bfqq->ref++; /* get a process reference to this queue */
|
|
bfq_log_bfqq(bfqd, bfqq, "get_queue, at end: %p, %d", bfqq, bfqq->ref);
|
|
rcu_read_unlock();
|
|
return bfqq;
|
|
}
|
|
|
|
static void bfq_update_io_thinktime(struct bfq_data *bfqd,
|
|
struct bfq_queue *bfqq)
|
|
{
|
|
struct bfq_ttime *ttime = &bfqq->ttime;
|
|
u64 elapsed = ktime_get_ns() - bfqq->ttime.last_end_request;
|
|
|
|
elapsed = min_t(u64, elapsed, 2ULL * bfqd->bfq_slice_idle);
|
|
|
|
ttime->ttime_samples = (7*bfqq->ttime.ttime_samples + 256) / 8;
|
|
ttime->ttime_total = div_u64(7*ttime->ttime_total + 256*elapsed, 8);
|
|
ttime->ttime_mean = div64_ul(ttime->ttime_total + 128,
|
|
ttime->ttime_samples);
|
|
}
|
|
|
|
static void
|
|
bfq_update_io_seektime(struct bfq_data *bfqd, struct bfq_queue *bfqq,
|
|
struct request *rq)
|
|
{
|
|
bfqq->seek_history <<= 1;
|
|
bfqq->seek_history |=
|
|
get_sdist(bfqq->last_request_pos, rq) > BFQQ_SEEK_THR &&
|
|
(!blk_queue_nonrot(bfqd->queue) ||
|
|
blk_rq_sectors(rq) < BFQQ_SECT_THR_NONROT);
|
|
}
|
|
|
|
/*
|
|
* Disable idle window if the process thinks too long or seeks so much that
|
|
* it doesn't matter.
|
|
*/
|
|
static void bfq_update_idle_window(struct bfq_data *bfqd,
|
|
struct bfq_queue *bfqq,
|
|
struct bfq_io_cq *bic)
|
|
{
|
|
int enable_idle;
|
|
|
|
/* Don't idle for async or idle io prio class. */
|
|
if (!bfq_bfqq_sync(bfqq) || bfq_class_idle(bfqq))
|
|
return;
|
|
|
|
/* Idle window just restored, statistics are meaningless. */
|
|
if (time_is_after_eq_jiffies(bfqq->split_time +
|
|
bfqd->bfq_wr_min_idle_time))
|
|
return;
|
|
|
|
enable_idle = bfq_bfqq_idle_window(bfqq);
|
|
|
|
if (atomic_read(&bic->icq.ioc->active_ref) == 0 ||
|
|
bfqd->bfq_slice_idle == 0 ||
|
|
(bfqd->hw_tag && BFQQ_SEEKY(bfqq) &&
|
|
bfqq->wr_coeff == 1))
|
|
enable_idle = 0;
|
|
else if (bfq_sample_valid(bfqq->ttime.ttime_samples)) {
|
|
if (bfqq->ttime.ttime_mean > bfqd->bfq_slice_idle &&
|
|
bfqq->wr_coeff == 1)
|
|
enable_idle = 0;
|
|
else
|
|
enable_idle = 1;
|
|
}
|
|
bfq_log_bfqq(bfqd, bfqq, "update_idle_window: enable_idle %d",
|
|
enable_idle);
|
|
|
|
if (enable_idle)
|
|
bfq_mark_bfqq_idle_window(bfqq);
|
|
else
|
|
bfq_clear_bfqq_idle_window(bfqq);
|
|
}
|
|
|
|
/*
|
|
* Called when a new fs request (rq) is added to bfqq. Check if there's
|
|
* something we should do about it.
|
|
*/
|
|
static void bfq_rq_enqueued(struct bfq_data *bfqd, struct bfq_queue *bfqq,
|
|
struct request *rq)
|
|
{
|
|
struct bfq_io_cq *bic = RQ_BIC(rq);
|
|
|
|
if (rq->cmd_flags & REQ_META)
|
|
bfqq->meta_pending++;
|
|
|
|
bfq_update_io_thinktime(bfqd, bfqq);
|
|
bfq_update_io_seektime(bfqd, bfqq, rq);
|
|
if (bfqq->entity.service > bfq_max_budget(bfqd) / 8 ||
|
|
!BFQQ_SEEKY(bfqq))
|
|
bfq_update_idle_window(bfqd, bfqq, bic);
|
|
|
|
bfq_log_bfqq(bfqd, bfqq,
|
|
"rq_enqueued: idle_window=%d (seeky %d)",
|
|
bfq_bfqq_idle_window(bfqq), BFQQ_SEEKY(bfqq));
|
|
|
|
bfqq->last_request_pos = blk_rq_pos(rq) + blk_rq_sectors(rq);
|
|
|
|
if (bfqq == bfqd->in_service_queue && bfq_bfqq_wait_request(bfqq)) {
|
|
bool small_req = bfqq->queued[rq_is_sync(rq)] == 1 &&
|
|
blk_rq_sectors(rq) < 32;
|
|
bool budget_timeout = bfq_bfqq_budget_timeout(bfqq);
|
|
|
|
/*
|
|
* There is just this request queued: if the request
|
|
* is small and the queue is not to be expired, then
|
|
* just exit.
|
|
*
|
|
* In this way, if the device is being idled to wait
|
|
* for a new request from the in-service queue, we
|
|
* avoid unplugging the device and committing the
|
|
* device to serve just a small request. On the
|
|
* contrary, we wait for the block layer to decide
|
|
* when to unplug the device: hopefully, new requests
|
|
* will be merged to this one quickly, then the device
|
|
* will be unplugged and larger requests will be
|
|
* dispatched.
|
|
*/
|
|
if (small_req && !budget_timeout)
|
|
return;
|
|
|
|
/*
|
|
* A large enough request arrived, or the queue is to
|
|
* be expired: in both cases disk idling is to be
|
|
* stopped, so clear wait_request flag and reset
|
|
* timer.
|
|
*/
|
|
bfq_clear_bfqq_wait_request(bfqq);
|
|
hrtimer_try_to_cancel(&bfqd->idle_slice_timer);
|
|
bfqg_stats_update_idle_time(bfqq_group(bfqq));
|
|
|
|
/*
|
|
* The queue is not empty, because a new request just
|
|
* arrived. Hence we can safely expire the queue, in
|
|
* case of budget timeout, without risking that the
|
|
* timestamps of the queue are not updated correctly.
|
|
* See [1] for more details.
|
|
*/
|
|
if (budget_timeout)
|
|
bfq_bfqq_expire(bfqd, bfqq, false,
|
|
BFQQE_BUDGET_TIMEOUT);
|
|
}
|
|
}
|
|
|
|
static void __bfq_insert_request(struct bfq_data *bfqd, struct request *rq)
|
|
{
|
|
struct bfq_queue *bfqq = RQ_BFQQ(rq),
|
|
*new_bfqq = bfq_setup_cooperator(bfqd, bfqq, rq, true);
|
|
|
|
if (new_bfqq) {
|
|
if (bic_to_bfqq(RQ_BIC(rq), 1) != bfqq)
|
|
new_bfqq = bic_to_bfqq(RQ_BIC(rq), 1);
|
|
/*
|
|
* Release the request's reference to the old bfqq
|
|
* and make sure one is taken to the shared queue.
|
|
*/
|
|
new_bfqq->allocated++;
|
|
bfqq->allocated--;
|
|
new_bfqq->ref++;
|
|
bfq_clear_bfqq_just_created(bfqq);
|
|
/*
|
|
* If the bic associated with the process
|
|
* issuing this request still points to bfqq
|
|
* (and thus has not been already redirected
|
|
* to new_bfqq or even some other bfq_queue),
|
|
* then complete the merge and redirect it to
|
|
* new_bfqq.
|
|
*/
|
|
if (bic_to_bfqq(RQ_BIC(rq), 1) == bfqq)
|
|
bfq_merge_bfqqs(bfqd, RQ_BIC(rq),
|
|
bfqq, new_bfqq);
|
|
/*
|
|
* rq is about to be enqueued into new_bfqq,
|
|
* release rq reference on bfqq
|
|
*/
|
|
bfq_put_queue(bfqq);
|
|
rq->elv.priv[1] = new_bfqq;
|
|
bfqq = new_bfqq;
|
|
}
|
|
|
|
bfq_add_request(rq);
|
|
|
|
rq->fifo_time = ktime_get_ns() + bfqd->bfq_fifo_expire[rq_is_sync(rq)];
|
|
list_add_tail(&rq->queuelist, &bfqq->fifo);
|
|
|
|
bfq_rq_enqueued(bfqd, bfqq, rq);
|
|
}
|
|
|
|
static void bfq_insert_request(struct blk_mq_hw_ctx *hctx, struct request *rq,
|
|
bool at_head)
|
|
{
|
|
struct request_queue *q = hctx->queue;
|
|
struct bfq_data *bfqd = q->elevator->elevator_data;
|
|
|
|
spin_lock_irq(&bfqd->lock);
|
|
if (blk_mq_sched_try_insert_merge(q, rq)) {
|
|
spin_unlock_irq(&bfqd->lock);
|
|
return;
|
|
}
|
|
|
|
spin_unlock_irq(&bfqd->lock);
|
|
|
|
blk_mq_sched_request_inserted(rq);
|
|
|
|
spin_lock_irq(&bfqd->lock);
|
|
if (at_head || blk_rq_is_passthrough(rq)) {
|
|
if (at_head)
|
|
list_add(&rq->queuelist, &bfqd->dispatch);
|
|
else
|
|
list_add_tail(&rq->queuelist, &bfqd->dispatch);
|
|
} else {
|
|
__bfq_insert_request(bfqd, rq);
|
|
|
|
if (rq_mergeable(rq)) {
|
|
elv_rqhash_add(q, rq);
|
|
if (!q->last_merge)
|
|
q->last_merge = rq;
|
|
}
|
|
}
|
|
|
|
spin_unlock_irq(&bfqd->lock);
|
|
}
|
|
|
|
static void bfq_insert_requests(struct blk_mq_hw_ctx *hctx,
|
|
struct list_head *list, bool at_head)
|
|
{
|
|
while (!list_empty(list)) {
|
|
struct request *rq;
|
|
|
|
rq = list_first_entry(list, struct request, queuelist);
|
|
list_del_init(&rq->queuelist);
|
|
bfq_insert_request(hctx, rq, at_head);
|
|
}
|
|
}
|
|
|
|
static void bfq_update_hw_tag(struct bfq_data *bfqd)
|
|
{
|
|
bfqd->max_rq_in_driver = max_t(int, bfqd->max_rq_in_driver,
|
|
bfqd->rq_in_driver);
|
|
|
|
if (bfqd->hw_tag == 1)
|
|
return;
|
|
|
|
/*
|
|
* This sample is valid if the number of outstanding requests
|
|
* is large enough to allow a queueing behavior. Note that the
|
|
* sum is not exact, as it's not taking into account deactivated
|
|
* requests.
|
|
*/
|
|
if (bfqd->rq_in_driver + bfqd->queued < BFQ_HW_QUEUE_THRESHOLD)
|
|
return;
|
|
|
|
if (bfqd->hw_tag_samples++ < BFQ_HW_QUEUE_SAMPLES)
|
|
return;
|
|
|
|
bfqd->hw_tag = bfqd->max_rq_in_driver > BFQ_HW_QUEUE_THRESHOLD;
|
|
bfqd->max_rq_in_driver = 0;
|
|
bfqd->hw_tag_samples = 0;
|
|
}
|
|
|
|
static void bfq_completed_request(struct bfq_queue *bfqq, struct bfq_data *bfqd)
|
|
{
|
|
u64 now_ns;
|
|
u32 delta_us;
|
|
|
|
bfq_update_hw_tag(bfqd);
|
|
|
|
bfqd->rq_in_driver--;
|
|
bfqq->dispatched--;
|
|
|
|
if (!bfqq->dispatched && !bfq_bfqq_busy(bfqq)) {
|
|
/*
|
|
* Set budget_timeout (which we overload to store the
|
|
* time at which the queue remains with no backlog and
|
|
* no outstanding request; used by the weight-raising
|
|
* mechanism).
|
|
*/
|
|
bfqq->budget_timeout = jiffies;
|
|
|
|
bfq_weights_tree_remove(bfqd, &bfqq->entity,
|
|
&bfqd->queue_weights_tree);
|
|
}
|
|
|
|
now_ns = ktime_get_ns();
|
|
|
|
bfqq->ttime.last_end_request = now_ns;
|
|
|
|
/*
|
|
* Using us instead of ns, to get a reasonable precision in
|
|
* computing rate in next check.
|
|
*/
|
|
delta_us = div_u64(now_ns - bfqd->last_completion, NSEC_PER_USEC);
|
|
|
|
/*
|
|
* If the request took rather long to complete, and, according
|
|
* to the maximum request size recorded, this completion latency
|
|
* implies that the request was certainly served at a very low
|
|
* rate (less than 1M sectors/sec), then the whole observation
|
|
* interval that lasts up to this time instant cannot be a
|
|
* valid time interval for computing a new peak rate. Invoke
|
|
* bfq_update_rate_reset to have the following three steps
|
|
* taken:
|
|
* - close the observation interval at the last (previous)
|
|
* request dispatch or completion
|
|
* - compute rate, if possible, for that observation interval
|
|
* - reset to zero samples, which will trigger a proper
|
|
* re-initialization of the observation interval on next
|
|
* dispatch
|
|
*/
|
|
if (delta_us > BFQ_MIN_TT/NSEC_PER_USEC &&
|
|
(bfqd->last_rq_max_size<<BFQ_RATE_SHIFT)/delta_us <
|
|
1UL<<(BFQ_RATE_SHIFT - 10))
|
|
bfq_update_rate_reset(bfqd, NULL);
|
|
bfqd->last_completion = now_ns;
|
|
|
|
/*
|
|
* If we are waiting to discover whether the request pattern
|
|
* of the task associated with the queue is actually
|
|
* isochronous, and both requisites for this condition to hold
|
|
* are now satisfied, then compute soft_rt_next_start (see the
|
|
* comments on the function bfq_bfqq_softrt_next_start()). We
|
|
* schedule this delayed check when bfqq expires, if it still
|
|
* has in-flight requests.
|
|
*/
|
|
if (bfq_bfqq_softrt_update(bfqq) && bfqq->dispatched == 0 &&
|
|
RB_EMPTY_ROOT(&bfqq->sort_list))
|
|
bfqq->soft_rt_next_start =
|
|
bfq_bfqq_softrt_next_start(bfqd, bfqq);
|
|
|
|
/*
|
|
* If this is the in-service queue, check if it needs to be expired,
|
|
* or if we want to idle in case it has no pending requests.
|
|
*/
|
|
if (bfqd->in_service_queue == bfqq) {
|
|
if (bfqq->dispatched == 0 && bfq_bfqq_must_idle(bfqq)) {
|
|
bfq_arm_slice_timer(bfqd);
|
|
return;
|
|
} else if (bfq_may_expire_for_budg_timeout(bfqq))
|
|
bfq_bfqq_expire(bfqd, bfqq, false,
|
|
BFQQE_BUDGET_TIMEOUT);
|
|
else if (RB_EMPTY_ROOT(&bfqq->sort_list) &&
|
|
(bfqq->dispatched == 0 ||
|
|
!bfq_bfqq_may_idle(bfqq)))
|
|
bfq_bfqq_expire(bfqd, bfqq, false,
|
|
BFQQE_NO_MORE_REQUESTS);
|
|
}
|
|
}
|
|
|
|
static void bfq_put_rq_priv_body(struct bfq_queue *bfqq)
|
|
{
|
|
bfqq->allocated--;
|
|
|
|
bfq_put_queue(bfqq);
|
|
}
|
|
|
|
static void bfq_finish_request(struct request *rq)
|
|
{
|
|
struct bfq_queue *bfqq;
|
|
struct bfq_data *bfqd;
|
|
|
|
if (!rq->elv.icq)
|
|
return;
|
|
|
|
bfqq = RQ_BFQQ(rq);
|
|
bfqd = bfqq->bfqd;
|
|
|
|
if (rq->rq_flags & RQF_STARTED)
|
|
bfqg_stats_update_completion(bfqq_group(bfqq),
|
|
rq_start_time_ns(rq),
|
|
rq_io_start_time_ns(rq),
|
|
rq->cmd_flags);
|
|
|
|
if (likely(rq->rq_flags & RQF_STARTED)) {
|
|
unsigned long flags;
|
|
|
|
spin_lock_irqsave(&bfqd->lock, flags);
|
|
|
|
bfq_completed_request(bfqq, bfqd);
|
|
bfq_put_rq_priv_body(bfqq);
|
|
|
|
spin_unlock_irqrestore(&bfqd->lock, flags);
|
|
} else {
|
|
/*
|
|
* Request rq may be still/already in the scheduler,
|
|
* in which case we need to remove it. And we cannot
|
|
* defer such a check and removal, to avoid
|
|
* inconsistencies in the time interval from the end
|
|
* of this function to the start of the deferred work.
|
|
* This situation seems to occur only in process
|
|
* context, as a consequence of a merge. In the
|
|
* current version of the code, this implies that the
|
|
* lock is held.
|
|
*/
|
|
|
|
if (!RB_EMPTY_NODE(&rq->rb_node))
|
|
bfq_remove_request(rq->q, rq);
|
|
bfq_put_rq_priv_body(bfqq);
|
|
}
|
|
|
|
rq->elv.priv[0] = NULL;
|
|
rq->elv.priv[1] = NULL;
|
|
}
|
|
|
|
/*
|
|
* Returns NULL if a new bfqq should be allocated, or the old bfqq if this
|
|
* was the last process referring to that bfqq.
|
|
*/
|
|
static struct bfq_queue *
|
|
bfq_split_bfqq(struct bfq_io_cq *bic, struct bfq_queue *bfqq)
|
|
{
|
|
bfq_log_bfqq(bfqq->bfqd, bfqq, "splitting queue");
|
|
|
|
if (bfqq_process_refs(bfqq) == 1) {
|
|
bfqq->pid = current->pid;
|
|
bfq_clear_bfqq_coop(bfqq);
|
|
bfq_clear_bfqq_split_coop(bfqq);
|
|
return bfqq;
|
|
}
|
|
|
|
bic_set_bfqq(bic, NULL, 1);
|
|
|
|
bfq_put_cooperator(bfqq);
|
|
|
|
bfq_put_queue(bfqq);
|
|
return NULL;
|
|
}
|
|
|
|
static struct bfq_queue *bfq_get_bfqq_handle_split(struct bfq_data *bfqd,
|
|
struct bfq_io_cq *bic,
|
|
struct bio *bio,
|
|
bool split, bool is_sync,
|
|
bool *new_queue)
|
|
{
|
|
struct bfq_queue *bfqq = bic_to_bfqq(bic, is_sync);
|
|
|
|
if (likely(bfqq && bfqq != &bfqd->oom_bfqq))
|
|
return bfqq;
|
|
|
|
if (new_queue)
|
|
*new_queue = true;
|
|
|
|
if (bfqq)
|
|
bfq_put_queue(bfqq);
|
|
bfqq = bfq_get_queue(bfqd, bio, is_sync, bic);
|
|
|
|
bic_set_bfqq(bic, bfqq, is_sync);
|
|
if (split && is_sync) {
|
|
if ((bic->was_in_burst_list && bfqd->large_burst) ||
|
|
bic->saved_in_large_burst)
|
|
bfq_mark_bfqq_in_large_burst(bfqq);
|
|
else {
|
|
bfq_clear_bfqq_in_large_burst(bfqq);
|
|
if (bic->was_in_burst_list)
|
|
hlist_add_head(&bfqq->burst_list_node,
|
|
&bfqd->burst_list);
|
|
}
|
|
bfqq->split_time = jiffies;
|
|
}
|
|
|
|
return bfqq;
|
|
}
|
|
|
|
/*
|
|
* Allocate bfq data structures associated with this request.
|
|
*/
|
|
static void bfq_prepare_request(struct request *rq, struct bio *bio)
|
|
{
|
|
struct request_queue *q = rq->q;
|
|
struct bfq_data *bfqd = q->elevator->elevator_data;
|
|
struct bfq_io_cq *bic;
|
|
const int is_sync = rq_is_sync(rq);
|
|
struct bfq_queue *bfqq;
|
|
bool new_queue = false;
|
|
bool bfqq_already_existing = false, split = false;
|
|
|
|
if (!rq->elv.icq)
|
|
return;
|
|
bic = icq_to_bic(rq->elv.icq);
|
|
|
|
spin_lock_irq(&bfqd->lock);
|
|
|
|
bfq_check_ioprio_change(bic, bio);
|
|
|
|
bfq_bic_update_cgroup(bic, bio);
|
|
|
|
bfqq = bfq_get_bfqq_handle_split(bfqd, bic, bio, false, is_sync,
|
|
&new_queue);
|
|
|
|
if (likely(!new_queue)) {
|
|
/* If the queue was seeky for too long, break it apart. */
|
|
if (bfq_bfqq_coop(bfqq) && bfq_bfqq_split_coop(bfqq)) {
|
|
bfq_log_bfqq(bfqd, bfqq, "breaking apart bfqq");
|
|
|
|
/* Update bic before losing reference to bfqq */
|
|
if (bfq_bfqq_in_large_burst(bfqq))
|
|
bic->saved_in_large_burst = true;
|
|
|
|
bfqq = bfq_split_bfqq(bic, bfqq);
|
|
split = true;
|
|
|
|
if (!bfqq)
|
|
bfqq = bfq_get_bfqq_handle_split(bfqd, bic, bio,
|
|
true, is_sync,
|
|
NULL);
|
|
else
|
|
bfqq_already_existing = true;
|
|
}
|
|
}
|
|
|
|
bfqq->allocated++;
|
|
bfqq->ref++;
|
|
bfq_log_bfqq(bfqd, bfqq, "get_request %p: bfqq %p, %d",
|
|
rq, bfqq, bfqq->ref);
|
|
|
|
rq->elv.priv[0] = bic;
|
|
rq->elv.priv[1] = bfqq;
|
|
|
|
/*
|
|
* If a bfq_queue has only one process reference, it is owned
|
|
* by only this bic: we can then set bfqq->bic = bic. in
|
|
* addition, if the queue has also just been split, we have to
|
|
* resume its state.
|
|
*/
|
|
if (likely(bfqq != &bfqd->oom_bfqq) && bfqq_process_refs(bfqq) == 1) {
|
|
bfqq->bic = bic;
|
|
if (split) {
|
|
/*
|
|
* The queue has just been split from a shared
|
|
* queue: restore the idle window and the
|
|
* possible weight raising period.
|
|
*/
|
|
bfq_bfqq_resume_state(bfqq, bfqd, bic,
|
|
bfqq_already_existing);
|
|
}
|
|
}
|
|
|
|
if (unlikely(bfq_bfqq_just_created(bfqq)))
|
|
bfq_handle_burst(bfqd, bfqq);
|
|
|
|
spin_unlock_irq(&bfqd->lock);
|
|
}
|
|
|
|
static void bfq_idle_slice_timer_body(struct bfq_queue *bfqq)
|
|
{
|
|
struct bfq_data *bfqd = bfqq->bfqd;
|
|
enum bfqq_expiration reason;
|
|
unsigned long flags;
|
|
|
|
spin_lock_irqsave(&bfqd->lock, flags);
|
|
bfq_clear_bfqq_wait_request(bfqq);
|
|
|
|
if (bfqq != bfqd->in_service_queue) {
|
|
spin_unlock_irqrestore(&bfqd->lock, flags);
|
|
return;
|
|
}
|
|
|
|
if (bfq_bfqq_budget_timeout(bfqq))
|
|
/*
|
|
* Also here the queue can be safely expired
|
|
* for budget timeout without wasting
|
|
* guarantees
|
|
*/
|
|
reason = BFQQE_BUDGET_TIMEOUT;
|
|
else if (bfqq->queued[0] == 0 && bfqq->queued[1] == 0)
|
|
/*
|
|
* The queue may not be empty upon timer expiration,
|
|
* because we may not disable the timer when the
|
|
* first request of the in-service queue arrives
|
|
* during disk idling.
|
|
*/
|
|
reason = BFQQE_TOO_IDLE;
|
|
else
|
|
goto schedule_dispatch;
|
|
|
|
bfq_bfqq_expire(bfqd, bfqq, true, reason);
|
|
|
|
schedule_dispatch:
|
|
spin_unlock_irqrestore(&bfqd->lock, flags);
|
|
bfq_schedule_dispatch(bfqd);
|
|
}
|
|
|
|
/*
|
|
* Handler of the expiration of the timer running if the in-service queue
|
|
* is idling inside its time slice.
|
|
*/
|
|
static enum hrtimer_restart bfq_idle_slice_timer(struct hrtimer *timer)
|
|
{
|
|
struct bfq_data *bfqd = container_of(timer, struct bfq_data,
|
|
idle_slice_timer);
|
|
struct bfq_queue *bfqq = bfqd->in_service_queue;
|
|
|
|
/*
|
|
* Theoretical race here: the in-service queue can be NULL or
|
|
* different from the queue that was idling if a new request
|
|
* arrives for the current queue and there is a full dispatch
|
|
* cycle that changes the in-service queue. This can hardly
|
|
* happen, but in the worst case we just expire a queue too
|
|
* early.
|
|
*/
|
|
if (bfqq)
|
|
bfq_idle_slice_timer_body(bfqq);
|
|
|
|
return HRTIMER_NORESTART;
|
|
}
|
|
|
|
static void __bfq_put_async_bfqq(struct bfq_data *bfqd,
|
|
struct bfq_queue **bfqq_ptr)
|
|
{
|
|
struct bfq_queue *bfqq = *bfqq_ptr;
|
|
|
|
bfq_log(bfqd, "put_async_bfqq: %p", bfqq);
|
|
if (bfqq) {
|
|
bfq_bfqq_move(bfqd, bfqq, bfqd->root_group);
|
|
|
|
bfq_log_bfqq(bfqd, bfqq, "put_async_bfqq: putting %p, %d",
|
|
bfqq, bfqq->ref);
|
|
bfq_put_queue(bfqq);
|
|
*bfqq_ptr = NULL;
|
|
}
|
|
}
|
|
|
|
/*
|
|
* Release all the bfqg references to its async queues. If we are
|
|
* deallocating the group these queues may still contain requests, so
|
|
* we reparent them to the root cgroup (i.e., the only one that will
|
|
* exist for sure until all the requests on a device are gone).
|
|
*/
|
|
void bfq_put_async_queues(struct bfq_data *bfqd, struct bfq_group *bfqg)
|
|
{
|
|
int i, j;
|
|
|
|
for (i = 0; i < 2; i++)
|
|
for (j = 0; j < IOPRIO_BE_NR; j++)
|
|
__bfq_put_async_bfqq(bfqd, &bfqg->async_bfqq[i][j]);
|
|
|
|
__bfq_put_async_bfqq(bfqd, &bfqg->async_idle_bfqq);
|
|
}
|
|
|
|
static void bfq_exit_queue(struct elevator_queue *e)
|
|
{
|
|
struct bfq_data *bfqd = e->elevator_data;
|
|
struct bfq_queue *bfqq, *n;
|
|
|
|
hrtimer_cancel(&bfqd->idle_slice_timer);
|
|
|
|
spin_lock_irq(&bfqd->lock);
|
|
list_for_each_entry_safe(bfqq, n, &bfqd->idle_list, bfqq_list)
|
|
bfq_deactivate_bfqq(bfqd, bfqq, false, false);
|
|
spin_unlock_irq(&bfqd->lock);
|
|
|
|
hrtimer_cancel(&bfqd->idle_slice_timer);
|
|
|
|
#ifdef CONFIG_BFQ_GROUP_IOSCHED
|
|
blkcg_deactivate_policy(bfqd->queue, &blkcg_policy_bfq);
|
|
#else
|
|
spin_lock_irq(&bfqd->lock);
|
|
bfq_put_async_queues(bfqd, bfqd->root_group);
|
|
kfree(bfqd->root_group);
|
|
spin_unlock_irq(&bfqd->lock);
|
|
#endif
|
|
|
|
kfree(bfqd);
|
|
}
|
|
|
|
static void bfq_init_root_group(struct bfq_group *root_group,
|
|
struct bfq_data *bfqd)
|
|
{
|
|
int i;
|
|
|
|
#ifdef CONFIG_BFQ_GROUP_IOSCHED
|
|
root_group->entity.parent = NULL;
|
|
root_group->my_entity = NULL;
|
|
root_group->bfqd = bfqd;
|
|
#endif
|
|
root_group->rq_pos_tree = RB_ROOT;
|
|
for (i = 0; i < BFQ_IOPRIO_CLASSES; i++)
|
|
root_group->sched_data.service_tree[i] = BFQ_SERVICE_TREE_INIT;
|
|
root_group->sched_data.bfq_class_idle_last_service = jiffies;
|
|
}
|
|
|
|
static int bfq_init_queue(struct request_queue *q, struct elevator_type *e)
|
|
{
|
|
struct bfq_data *bfqd;
|
|
struct elevator_queue *eq;
|
|
|
|
eq = elevator_alloc(q, e);
|
|
if (!eq)
|
|
return -ENOMEM;
|
|
|
|
bfqd = kzalloc_node(sizeof(*bfqd), GFP_KERNEL, q->node);
|
|
if (!bfqd) {
|
|
kobject_put(&eq->kobj);
|
|
return -ENOMEM;
|
|
}
|
|
eq->elevator_data = bfqd;
|
|
|
|
spin_lock_irq(q->queue_lock);
|
|
q->elevator = eq;
|
|
spin_unlock_irq(q->queue_lock);
|
|
|
|
/*
|
|
* Our fallback bfqq if bfq_find_alloc_queue() runs into OOM issues.
|
|
* Grab a permanent reference to it, so that the normal code flow
|
|
* will not attempt to free it.
|
|
*/
|
|
bfq_init_bfqq(bfqd, &bfqd->oom_bfqq, NULL, 1, 0);
|
|
bfqd->oom_bfqq.ref++;
|
|
bfqd->oom_bfqq.new_ioprio = BFQ_DEFAULT_QUEUE_IOPRIO;
|
|
bfqd->oom_bfqq.new_ioprio_class = IOPRIO_CLASS_BE;
|
|
bfqd->oom_bfqq.entity.new_weight =
|
|
bfq_ioprio_to_weight(bfqd->oom_bfqq.new_ioprio);
|
|
|
|
/* oom_bfqq does not participate to bursts */
|
|
bfq_clear_bfqq_just_created(&bfqd->oom_bfqq);
|
|
|
|
/*
|
|
* Trigger weight initialization, according to ioprio, at the
|
|
* oom_bfqq's first activation. The oom_bfqq's ioprio and ioprio
|
|
* class won't be changed any more.
|
|
*/
|
|
bfqd->oom_bfqq.entity.prio_changed = 1;
|
|
|
|
bfqd->queue = q;
|
|
|
|
INIT_LIST_HEAD(&bfqd->dispatch);
|
|
|
|
hrtimer_init(&bfqd->idle_slice_timer, CLOCK_MONOTONIC,
|
|
HRTIMER_MODE_REL);
|
|
bfqd->idle_slice_timer.function = bfq_idle_slice_timer;
|
|
|
|
bfqd->queue_weights_tree = RB_ROOT;
|
|
bfqd->group_weights_tree = RB_ROOT;
|
|
|
|
INIT_LIST_HEAD(&bfqd->active_list);
|
|
INIT_LIST_HEAD(&bfqd->idle_list);
|
|
INIT_HLIST_HEAD(&bfqd->burst_list);
|
|
|
|
bfqd->hw_tag = -1;
|
|
|
|
bfqd->bfq_max_budget = bfq_default_max_budget;
|
|
|
|
bfqd->bfq_fifo_expire[0] = bfq_fifo_expire[0];
|
|
bfqd->bfq_fifo_expire[1] = bfq_fifo_expire[1];
|
|
bfqd->bfq_back_max = bfq_back_max;
|
|
bfqd->bfq_back_penalty = bfq_back_penalty;
|
|
bfqd->bfq_slice_idle = bfq_slice_idle;
|
|
bfqd->bfq_timeout = bfq_timeout;
|
|
|
|
bfqd->bfq_requests_within_timer = 120;
|
|
|
|
bfqd->bfq_large_burst_thresh = 8;
|
|
bfqd->bfq_burst_interval = msecs_to_jiffies(180);
|
|
|
|
bfqd->low_latency = true;
|
|
|
|
/*
|
|
* Trade-off between responsiveness and fairness.
|
|
*/
|
|
bfqd->bfq_wr_coeff = 30;
|
|
bfqd->bfq_wr_rt_max_time = msecs_to_jiffies(300);
|
|
bfqd->bfq_wr_max_time = 0;
|
|
bfqd->bfq_wr_min_idle_time = msecs_to_jiffies(2000);
|
|
bfqd->bfq_wr_min_inter_arr_async = msecs_to_jiffies(500);
|
|
bfqd->bfq_wr_max_softrt_rate = 7000; /*
|
|
* Approximate rate required
|
|
* to playback or record a
|
|
* high-definition compressed
|
|
* video.
|
|
*/
|
|
bfqd->wr_busy_queues = 0;
|
|
|
|
/*
|
|
* Begin by assuming, optimistically, that the device is a
|
|
* high-speed one, and that its peak rate is equal to 2/3 of
|
|
* the highest reference rate.
|
|
*/
|
|
bfqd->RT_prod = R_fast[blk_queue_nonrot(bfqd->queue)] *
|
|
T_fast[blk_queue_nonrot(bfqd->queue)];
|
|
bfqd->peak_rate = R_fast[blk_queue_nonrot(bfqd->queue)] * 2 / 3;
|
|
bfqd->device_speed = BFQ_BFQD_FAST;
|
|
|
|
spin_lock_init(&bfqd->lock);
|
|
|
|
/*
|
|
* The invocation of the next bfq_create_group_hierarchy
|
|
* function is the head of a chain of function calls
|
|
* (bfq_create_group_hierarchy->blkcg_activate_policy->
|
|
* blk_mq_freeze_queue) that may lead to the invocation of the
|
|
* has_work hook function. For this reason,
|
|
* bfq_create_group_hierarchy is invoked only after all
|
|
* scheduler data has been initialized, apart from the fields
|
|
* that can be initialized only after invoking
|
|
* bfq_create_group_hierarchy. This, in particular, enables
|
|
* has_work to correctly return false. Of course, to avoid
|
|
* other inconsistencies, the blk-mq stack must then refrain
|
|
* from invoking further scheduler hooks before this init
|
|
* function is finished.
|
|
*/
|
|
bfqd->root_group = bfq_create_group_hierarchy(bfqd, q->node);
|
|
if (!bfqd->root_group)
|
|
goto out_free;
|
|
bfq_init_root_group(bfqd->root_group, bfqd);
|
|
bfq_init_entity(&bfqd->oom_bfqq.entity, bfqd->root_group);
|
|
|
|
|
|
return 0;
|
|
|
|
out_free:
|
|
kfree(bfqd);
|
|
kobject_put(&eq->kobj);
|
|
return -ENOMEM;
|
|
}
|
|
|
|
static void bfq_slab_kill(void)
|
|
{
|
|
kmem_cache_destroy(bfq_pool);
|
|
}
|
|
|
|
static int __init bfq_slab_setup(void)
|
|
{
|
|
bfq_pool = KMEM_CACHE(bfq_queue, 0);
|
|
if (!bfq_pool)
|
|
return -ENOMEM;
|
|
return 0;
|
|
}
|
|
|
|
static ssize_t bfq_var_show(unsigned int var, char *page)
|
|
{
|
|
return sprintf(page, "%u\n", var);
|
|
}
|
|
|
|
static ssize_t bfq_var_store(unsigned long *var, const char *page,
|
|
size_t count)
|
|
{
|
|
unsigned long new_val;
|
|
int ret = kstrtoul(page, 10, &new_val);
|
|
|
|
if (ret == 0)
|
|
*var = new_val;
|
|
|
|
return count;
|
|
}
|
|
|
|
#define SHOW_FUNCTION(__FUNC, __VAR, __CONV) \
|
|
static ssize_t __FUNC(struct elevator_queue *e, char *page) \
|
|
{ \
|
|
struct bfq_data *bfqd = e->elevator_data; \
|
|
u64 __data = __VAR; \
|
|
if (__CONV == 1) \
|
|
__data = jiffies_to_msecs(__data); \
|
|
else if (__CONV == 2) \
|
|
__data = div_u64(__data, NSEC_PER_MSEC); \
|
|
return bfq_var_show(__data, (page)); \
|
|
}
|
|
SHOW_FUNCTION(bfq_fifo_expire_sync_show, bfqd->bfq_fifo_expire[1], 2);
|
|
SHOW_FUNCTION(bfq_fifo_expire_async_show, bfqd->bfq_fifo_expire[0], 2);
|
|
SHOW_FUNCTION(bfq_back_seek_max_show, bfqd->bfq_back_max, 0);
|
|
SHOW_FUNCTION(bfq_back_seek_penalty_show, bfqd->bfq_back_penalty, 0);
|
|
SHOW_FUNCTION(bfq_slice_idle_show, bfqd->bfq_slice_idle, 2);
|
|
SHOW_FUNCTION(bfq_max_budget_show, bfqd->bfq_user_max_budget, 0);
|
|
SHOW_FUNCTION(bfq_timeout_sync_show, bfqd->bfq_timeout, 1);
|
|
SHOW_FUNCTION(bfq_strict_guarantees_show, bfqd->strict_guarantees, 0);
|
|
SHOW_FUNCTION(bfq_low_latency_show, bfqd->low_latency, 0);
|
|
#undef SHOW_FUNCTION
|
|
|
|
#define USEC_SHOW_FUNCTION(__FUNC, __VAR) \
|
|
static ssize_t __FUNC(struct elevator_queue *e, char *page) \
|
|
{ \
|
|
struct bfq_data *bfqd = e->elevator_data; \
|
|
u64 __data = __VAR; \
|
|
__data = div_u64(__data, NSEC_PER_USEC); \
|
|
return bfq_var_show(__data, (page)); \
|
|
}
|
|
USEC_SHOW_FUNCTION(bfq_slice_idle_us_show, bfqd->bfq_slice_idle);
|
|
#undef USEC_SHOW_FUNCTION
|
|
|
|
#define STORE_FUNCTION(__FUNC, __PTR, MIN, MAX, __CONV) \
|
|
static ssize_t \
|
|
__FUNC(struct elevator_queue *e, const char *page, size_t count) \
|
|
{ \
|
|
struct bfq_data *bfqd = e->elevator_data; \
|
|
unsigned long uninitialized_var(__data); \
|
|
int ret = bfq_var_store(&__data, (page), count); \
|
|
if (__data < (MIN)) \
|
|
__data = (MIN); \
|
|
else if (__data > (MAX)) \
|
|
__data = (MAX); \
|
|
if (__CONV == 1) \
|
|
*(__PTR) = msecs_to_jiffies(__data); \
|
|
else if (__CONV == 2) \
|
|
*(__PTR) = (u64)__data * NSEC_PER_MSEC; \
|
|
else \
|
|
*(__PTR) = __data; \
|
|
return ret; \
|
|
}
|
|
STORE_FUNCTION(bfq_fifo_expire_sync_store, &bfqd->bfq_fifo_expire[1], 1,
|
|
INT_MAX, 2);
|
|
STORE_FUNCTION(bfq_fifo_expire_async_store, &bfqd->bfq_fifo_expire[0], 1,
|
|
INT_MAX, 2);
|
|
STORE_FUNCTION(bfq_back_seek_max_store, &bfqd->bfq_back_max, 0, INT_MAX, 0);
|
|
STORE_FUNCTION(bfq_back_seek_penalty_store, &bfqd->bfq_back_penalty, 1,
|
|
INT_MAX, 0);
|
|
STORE_FUNCTION(bfq_slice_idle_store, &bfqd->bfq_slice_idle, 0, INT_MAX, 2);
|
|
#undef STORE_FUNCTION
|
|
|
|
#define USEC_STORE_FUNCTION(__FUNC, __PTR, MIN, MAX) \
|
|
static ssize_t __FUNC(struct elevator_queue *e, const char *page, size_t count)\
|
|
{ \
|
|
struct bfq_data *bfqd = e->elevator_data; \
|
|
unsigned long uninitialized_var(__data); \
|
|
int ret = bfq_var_store(&__data, (page), count); \
|
|
if (__data < (MIN)) \
|
|
__data = (MIN); \
|
|
else if (__data > (MAX)) \
|
|
__data = (MAX); \
|
|
*(__PTR) = (u64)__data * NSEC_PER_USEC; \
|
|
return ret; \
|
|
}
|
|
USEC_STORE_FUNCTION(bfq_slice_idle_us_store, &bfqd->bfq_slice_idle, 0,
|
|
UINT_MAX);
|
|
#undef USEC_STORE_FUNCTION
|
|
|
|
static ssize_t bfq_max_budget_store(struct elevator_queue *e,
|
|
const char *page, size_t count)
|
|
{
|
|
struct bfq_data *bfqd = e->elevator_data;
|
|
unsigned long uninitialized_var(__data);
|
|
int ret = bfq_var_store(&__data, (page), count);
|
|
|
|
if (__data == 0)
|
|
bfqd->bfq_max_budget = bfq_calc_max_budget(bfqd);
|
|
else {
|
|
if (__data > INT_MAX)
|
|
__data = INT_MAX;
|
|
bfqd->bfq_max_budget = __data;
|
|
}
|
|
|
|
bfqd->bfq_user_max_budget = __data;
|
|
|
|
return ret;
|
|
}
|
|
|
|
/*
|
|
* Leaving this name to preserve name compatibility with cfq
|
|
* parameters, but this timeout is used for both sync and async.
|
|
*/
|
|
static ssize_t bfq_timeout_sync_store(struct elevator_queue *e,
|
|
const char *page, size_t count)
|
|
{
|
|
struct bfq_data *bfqd = e->elevator_data;
|
|
unsigned long uninitialized_var(__data);
|
|
int ret = bfq_var_store(&__data, (page), count);
|
|
|
|
if (__data < 1)
|
|
__data = 1;
|
|
else if (__data > INT_MAX)
|
|
__data = INT_MAX;
|
|
|
|
bfqd->bfq_timeout = msecs_to_jiffies(__data);
|
|
if (bfqd->bfq_user_max_budget == 0)
|
|
bfqd->bfq_max_budget = bfq_calc_max_budget(bfqd);
|
|
|
|
return ret;
|
|
}
|
|
|
|
static ssize_t bfq_strict_guarantees_store(struct elevator_queue *e,
|
|
const char *page, size_t count)
|
|
{
|
|
struct bfq_data *bfqd = e->elevator_data;
|
|
unsigned long uninitialized_var(__data);
|
|
int ret = bfq_var_store(&__data, (page), count);
|
|
|
|
if (__data > 1)
|
|
__data = 1;
|
|
if (!bfqd->strict_guarantees && __data == 1
|
|
&& bfqd->bfq_slice_idle < 8 * NSEC_PER_MSEC)
|
|
bfqd->bfq_slice_idle = 8 * NSEC_PER_MSEC;
|
|
|
|
bfqd->strict_guarantees = __data;
|
|
|
|
return ret;
|
|
}
|
|
|
|
static ssize_t bfq_low_latency_store(struct elevator_queue *e,
|
|
const char *page, size_t count)
|
|
{
|
|
struct bfq_data *bfqd = e->elevator_data;
|
|
unsigned long uninitialized_var(__data);
|
|
int ret = bfq_var_store(&__data, (page), count);
|
|
|
|
if (__data > 1)
|
|
__data = 1;
|
|
if (__data == 0 && bfqd->low_latency != 0)
|
|
bfq_end_wr(bfqd);
|
|
bfqd->low_latency = __data;
|
|
|
|
return ret;
|
|
}
|
|
|
|
#define BFQ_ATTR(name) \
|
|
__ATTR(name, 0644, bfq_##name##_show, bfq_##name##_store)
|
|
|
|
static struct elv_fs_entry bfq_attrs[] = {
|
|
BFQ_ATTR(fifo_expire_sync),
|
|
BFQ_ATTR(fifo_expire_async),
|
|
BFQ_ATTR(back_seek_max),
|
|
BFQ_ATTR(back_seek_penalty),
|
|
BFQ_ATTR(slice_idle),
|
|
BFQ_ATTR(slice_idle_us),
|
|
BFQ_ATTR(max_budget),
|
|
BFQ_ATTR(timeout_sync),
|
|
BFQ_ATTR(strict_guarantees),
|
|
BFQ_ATTR(low_latency),
|
|
__ATTR_NULL
|
|
};
|
|
|
|
static struct elevator_type iosched_bfq_mq = {
|
|
.ops.mq = {
|
|
.prepare_request = bfq_prepare_request,
|
|
.finish_request = bfq_finish_request,
|
|
.exit_icq = bfq_exit_icq,
|
|
.insert_requests = bfq_insert_requests,
|
|
.dispatch_request = bfq_dispatch_request,
|
|
.next_request = elv_rb_latter_request,
|
|
.former_request = elv_rb_former_request,
|
|
.allow_merge = bfq_allow_bio_merge,
|
|
.bio_merge = bfq_bio_merge,
|
|
.request_merge = bfq_request_merge,
|
|
.requests_merged = bfq_requests_merged,
|
|
.request_merged = bfq_request_merged,
|
|
.has_work = bfq_has_work,
|
|
.init_sched = bfq_init_queue,
|
|
.exit_sched = bfq_exit_queue,
|
|
},
|
|
|
|
.uses_mq = true,
|
|
.icq_size = sizeof(struct bfq_io_cq),
|
|
.icq_align = __alignof__(struct bfq_io_cq),
|
|
.elevator_attrs = bfq_attrs,
|
|
.elevator_name = "bfq",
|
|
.elevator_owner = THIS_MODULE,
|
|
};
|
|
|
|
static int __init bfq_init(void)
|
|
{
|
|
int ret;
|
|
|
|
#ifdef CONFIG_BFQ_GROUP_IOSCHED
|
|
ret = blkcg_policy_register(&blkcg_policy_bfq);
|
|
if (ret)
|
|
return ret;
|
|
#endif
|
|
|
|
ret = -ENOMEM;
|
|
if (bfq_slab_setup())
|
|
goto err_pol_unreg;
|
|
|
|
/*
|
|
* Times to load large popular applications for the typical
|
|
* systems installed on the reference devices (see the
|
|
* comments before the definitions of the next two
|
|
* arrays). Actually, we use slightly slower values, as the
|
|
* estimated peak rate tends to be smaller than the actual
|
|
* peak rate. The reason for this last fact is that estimates
|
|
* are computed over much shorter time intervals than the long
|
|
* intervals typically used for benchmarking. Why? First, to
|
|
* adapt more quickly to variations. Second, because an I/O
|
|
* scheduler cannot rely on a peak-rate-evaluation workload to
|
|
* be run for a long time.
|
|
*/
|
|
T_slow[0] = msecs_to_jiffies(3500); /* actually 4 sec */
|
|
T_slow[1] = msecs_to_jiffies(6000); /* actually 6.5 sec */
|
|
T_fast[0] = msecs_to_jiffies(7000); /* actually 8 sec */
|
|
T_fast[1] = msecs_to_jiffies(2500); /* actually 3 sec */
|
|
|
|
/*
|
|
* Thresholds that determine the switch between speed classes
|
|
* (see the comments before the definition of the array
|
|
* device_speed_thresh). These thresholds are biased towards
|
|
* transitions to the fast class. This is safer than the
|
|
* opposite bias. In fact, a wrong transition to the slow
|
|
* class results in short weight-raising periods, because the
|
|
* speed of the device then tends to be higher that the
|
|
* reference peak rate. On the opposite end, a wrong
|
|
* transition to the fast class tends to increase
|
|
* weight-raising periods, because of the opposite reason.
|
|
*/
|
|
device_speed_thresh[0] = (4 * R_slow[0]) / 3;
|
|
device_speed_thresh[1] = (4 * R_slow[1]) / 3;
|
|
|
|
ret = elv_register(&iosched_bfq_mq);
|
|
if (ret)
|
|
goto err_pol_unreg;
|
|
|
|
return 0;
|
|
|
|
err_pol_unreg:
|
|
#ifdef CONFIG_BFQ_GROUP_IOSCHED
|
|
blkcg_policy_unregister(&blkcg_policy_bfq);
|
|
#endif
|
|
return ret;
|
|
}
|
|
|
|
static void __exit bfq_exit(void)
|
|
{
|
|
elv_unregister(&iosched_bfq_mq);
|
|
#ifdef CONFIG_BFQ_GROUP_IOSCHED
|
|
blkcg_policy_unregister(&blkcg_policy_bfq);
|
|
#endif
|
|
bfq_slab_kill();
|
|
}
|
|
|
|
module_init(bfq_init);
|
|
module_exit(bfq_exit);
|
|
|
|
MODULE_AUTHOR("Paolo Valente");
|
|
MODULE_LICENSE("GPL");
|
|
MODULE_DESCRIPTION("MQ Budget Fair Queueing I/O Scheduler");
|