![Yafang Shao](/assets/img/avatar_default.png)
The task->flags is a 32-bits flag, in which 31 bits have already been consumed. So it is hardly to introduce other new per process flag. Currently there're still enough spaces in the bit-field section of task_struct, so we can define the memstall state as a single bit in task_struct instead. This patch also removes an out-of-date comment pointed by Matthew. Suggested-by: Johannes Weiner <hannes@cmpxchg.org> Signed-off-by: Yafang Shao <laoar.shao@gmail.com> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> Acked-by: Johannes Weiner <hannes@cmpxchg.org> Link: https://lkml.kernel.org/r/1584408485-1921-1-git-send-email-laoar.shao@gmail.com
1344 lines
37 KiB
C
1344 lines
37 KiB
C
/*
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* Pressure stall information for CPU, memory and IO
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*
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* Copyright (c) 2018 Facebook, Inc.
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* Author: Johannes Weiner <hannes@cmpxchg.org>
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*
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* Polling support by Suren Baghdasaryan <surenb@google.com>
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* Copyright (c) 2018 Google, Inc.
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*
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* When CPU, memory and IO are contended, tasks experience delays that
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* reduce throughput and introduce latencies into the workload. Memory
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* and IO contention, in addition, can cause a full loss of forward
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* progress in which the CPU goes idle.
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*
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* This code aggregates individual task delays into resource pressure
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* metrics that indicate problems with both workload health and
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* resource utilization.
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*
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* Model
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*
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* The time in which a task can execute on a CPU is our baseline for
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* productivity. Pressure expresses the amount of time in which this
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* potential cannot be realized due to resource contention.
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*
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* This concept of productivity has two components: the workload and
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* the CPU. To measure the impact of pressure on both, we define two
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* contention states for a resource: SOME and FULL.
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*
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* In the SOME state of a given resource, one or more tasks are
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* delayed on that resource. This affects the workload's ability to
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* perform work, but the CPU may still be executing other tasks.
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*
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* In the FULL state of a given resource, all non-idle tasks are
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* delayed on that resource such that nobody is advancing and the CPU
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* goes idle. This leaves both workload and CPU unproductive.
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*
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* (Naturally, the FULL state doesn't exist for the CPU resource.)
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*
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* SOME = nr_delayed_tasks != 0
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* FULL = nr_delayed_tasks != 0 && nr_running_tasks == 0
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*
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* The percentage of wallclock time spent in those compound stall
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* states gives pressure numbers between 0 and 100 for each resource,
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* where the SOME percentage indicates workload slowdowns and the FULL
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* percentage indicates reduced CPU utilization:
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*
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* %SOME = time(SOME) / period
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* %FULL = time(FULL) / period
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*
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* Multiple CPUs
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*
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* The more tasks and available CPUs there are, the more work can be
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* performed concurrently. This means that the potential that can go
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* unrealized due to resource contention *also* scales with non-idle
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* tasks and CPUs.
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*
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* Consider a scenario where 257 number crunching tasks are trying to
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* run concurrently on 256 CPUs. If we simply aggregated the task
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* states, we would have to conclude a CPU SOME pressure number of
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* 100%, since *somebody* is waiting on a runqueue at all
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* times. However, that is clearly not the amount of contention the
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* workload is experiencing: only one out of 256 possible exceution
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* threads will be contended at any given time, or about 0.4%.
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*
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* Conversely, consider a scenario of 4 tasks and 4 CPUs where at any
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* given time *one* of the tasks is delayed due to a lack of memory.
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* Again, looking purely at the task state would yield a memory FULL
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* pressure number of 0%, since *somebody* is always making forward
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* progress. But again this wouldn't capture the amount of execution
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* potential lost, which is 1 out of 4 CPUs, or 25%.
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*
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* To calculate wasted potential (pressure) with multiple processors,
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* we have to base our calculation on the number of non-idle tasks in
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* conjunction with the number of available CPUs, which is the number
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* of potential execution threads. SOME becomes then the proportion of
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* delayed tasks to possibe threads, and FULL is the share of possible
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* threads that are unproductive due to delays:
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*
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* threads = min(nr_nonidle_tasks, nr_cpus)
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* SOME = min(nr_delayed_tasks / threads, 1)
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* FULL = (threads - min(nr_running_tasks, threads)) / threads
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*
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* For the 257 number crunchers on 256 CPUs, this yields:
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*
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* threads = min(257, 256)
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* SOME = min(1 / 256, 1) = 0.4%
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* FULL = (256 - min(257, 256)) / 256 = 0%
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*
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* For the 1 out of 4 memory-delayed tasks, this yields:
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*
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* threads = min(4, 4)
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* SOME = min(1 / 4, 1) = 25%
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* FULL = (4 - min(3, 4)) / 4 = 25%
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*
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* [ Substitute nr_cpus with 1, and you can see that it's a natural
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* extension of the single-CPU model. ]
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*
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* Implementation
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*
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* To assess the precise time spent in each such state, we would have
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* to freeze the system on task changes and start/stop the state
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* clocks accordingly. Obviously that doesn't scale in practice.
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*
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* Because the scheduler aims to distribute the compute load evenly
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* among the available CPUs, we can track task state locally to each
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* CPU and, at much lower frequency, extrapolate the global state for
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* the cumulative stall times and the running averages.
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*
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* For each runqueue, we track:
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*
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* tSOME[cpu] = time(nr_delayed_tasks[cpu] != 0)
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* tFULL[cpu] = time(nr_delayed_tasks[cpu] && !nr_running_tasks[cpu])
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* tNONIDLE[cpu] = time(nr_nonidle_tasks[cpu] != 0)
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*
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* and then periodically aggregate:
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*
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* tNONIDLE = sum(tNONIDLE[i])
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*
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* tSOME = sum(tSOME[i] * tNONIDLE[i]) / tNONIDLE
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* tFULL = sum(tFULL[i] * tNONIDLE[i]) / tNONIDLE
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*
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* %SOME = tSOME / period
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* %FULL = tFULL / period
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*
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* This gives us an approximation of pressure that is practical
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* cost-wise, yet way more sensitive and accurate than periodic
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* sampling of the aggregate task states would be.
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*/
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#include "../workqueue_internal.h"
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#include <linux/sched/loadavg.h>
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#include <linux/seq_file.h>
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#include <linux/proc_fs.h>
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#include <linux/seqlock.h>
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#include <linux/uaccess.h>
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#include <linux/cgroup.h>
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#include <linux/module.h>
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#include <linux/sched.h>
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#include <linux/ctype.h>
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#include <linux/file.h>
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#include <linux/poll.h>
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#include <linux/psi.h>
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#include "sched.h"
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static int psi_bug __read_mostly;
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DEFINE_STATIC_KEY_FALSE(psi_disabled);
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#ifdef CONFIG_PSI_DEFAULT_DISABLED
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static bool psi_enable;
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#else
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static bool psi_enable = true;
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#endif
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static int __init setup_psi(char *str)
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{
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return kstrtobool(str, &psi_enable) == 0;
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}
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__setup("psi=", setup_psi);
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/* Running averages - we need to be higher-res than loadavg */
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#define PSI_FREQ (2*HZ+1) /* 2 sec intervals */
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#define EXP_10s 1677 /* 1/exp(2s/10s) as fixed-point */
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#define EXP_60s 1981 /* 1/exp(2s/60s) */
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#define EXP_300s 2034 /* 1/exp(2s/300s) */
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/* PSI trigger definitions */
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#define WINDOW_MIN_US 500000 /* Min window size is 500ms */
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#define WINDOW_MAX_US 10000000 /* Max window size is 10s */
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#define UPDATES_PER_WINDOW 10 /* 10 updates per window */
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/* Sampling frequency in nanoseconds */
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static u64 psi_period __read_mostly;
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/* System-level pressure and stall tracking */
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static DEFINE_PER_CPU(struct psi_group_cpu, system_group_pcpu);
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struct psi_group psi_system = {
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.pcpu = &system_group_pcpu,
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};
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static void psi_avgs_work(struct work_struct *work);
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static void group_init(struct psi_group *group)
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{
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int cpu;
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for_each_possible_cpu(cpu)
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seqcount_init(&per_cpu_ptr(group->pcpu, cpu)->seq);
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group->avg_last_update = sched_clock();
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group->avg_next_update = group->avg_last_update + psi_period;
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INIT_DELAYED_WORK(&group->avgs_work, psi_avgs_work);
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mutex_init(&group->avgs_lock);
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/* Init trigger-related members */
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atomic_set(&group->poll_scheduled, 0);
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mutex_init(&group->trigger_lock);
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INIT_LIST_HEAD(&group->triggers);
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memset(group->nr_triggers, 0, sizeof(group->nr_triggers));
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group->poll_states = 0;
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group->poll_min_period = U32_MAX;
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memset(group->polling_total, 0, sizeof(group->polling_total));
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group->polling_next_update = ULLONG_MAX;
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group->polling_until = 0;
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rcu_assign_pointer(group->poll_kworker, NULL);
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}
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void __init psi_init(void)
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{
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if (!psi_enable) {
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static_branch_enable(&psi_disabled);
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return;
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}
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psi_period = jiffies_to_nsecs(PSI_FREQ);
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group_init(&psi_system);
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}
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static bool test_state(unsigned int *tasks, enum psi_states state)
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{
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switch (state) {
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case PSI_IO_SOME:
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return tasks[NR_IOWAIT];
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case PSI_IO_FULL:
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return tasks[NR_IOWAIT] && !tasks[NR_RUNNING];
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case PSI_MEM_SOME:
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return tasks[NR_MEMSTALL];
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case PSI_MEM_FULL:
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return tasks[NR_MEMSTALL] && !tasks[NR_RUNNING];
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case PSI_CPU_SOME:
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return tasks[NR_RUNNING] > tasks[NR_ONCPU];
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case PSI_NONIDLE:
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return tasks[NR_IOWAIT] || tasks[NR_MEMSTALL] ||
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tasks[NR_RUNNING];
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default:
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return false;
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}
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}
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static void get_recent_times(struct psi_group *group, int cpu,
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enum psi_aggregators aggregator, u32 *times,
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u32 *pchanged_states)
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{
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struct psi_group_cpu *groupc = per_cpu_ptr(group->pcpu, cpu);
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u64 now, state_start;
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enum psi_states s;
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unsigned int seq;
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u32 state_mask;
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*pchanged_states = 0;
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/* Snapshot a coherent view of the CPU state */
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do {
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seq = read_seqcount_begin(&groupc->seq);
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now = cpu_clock(cpu);
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memcpy(times, groupc->times, sizeof(groupc->times));
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state_mask = groupc->state_mask;
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state_start = groupc->state_start;
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} while (read_seqcount_retry(&groupc->seq, seq));
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/* Calculate state time deltas against the previous snapshot */
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for (s = 0; s < NR_PSI_STATES; s++) {
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u32 delta;
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/*
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* In addition to already concluded states, we also
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* incorporate currently active states on the CPU,
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* since states may last for many sampling periods.
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*
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* This way we keep our delta sampling buckets small
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* (u32) and our reported pressure close to what's
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* actually happening.
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*/
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if (state_mask & (1 << s))
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times[s] += now - state_start;
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delta = times[s] - groupc->times_prev[aggregator][s];
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groupc->times_prev[aggregator][s] = times[s];
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times[s] = delta;
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if (delta)
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*pchanged_states |= (1 << s);
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}
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}
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static void calc_avgs(unsigned long avg[3], int missed_periods,
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u64 time, u64 period)
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{
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unsigned long pct;
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/* Fill in zeroes for periods of no activity */
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if (missed_periods) {
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avg[0] = calc_load_n(avg[0], EXP_10s, 0, missed_periods);
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avg[1] = calc_load_n(avg[1], EXP_60s, 0, missed_periods);
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avg[2] = calc_load_n(avg[2], EXP_300s, 0, missed_periods);
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}
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/* Sample the most recent active period */
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pct = div_u64(time * 100, period);
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pct *= FIXED_1;
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avg[0] = calc_load(avg[0], EXP_10s, pct);
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avg[1] = calc_load(avg[1], EXP_60s, pct);
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avg[2] = calc_load(avg[2], EXP_300s, pct);
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}
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static void collect_percpu_times(struct psi_group *group,
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enum psi_aggregators aggregator,
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u32 *pchanged_states)
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{
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u64 deltas[NR_PSI_STATES - 1] = { 0, };
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unsigned long nonidle_total = 0;
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u32 changed_states = 0;
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int cpu;
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int s;
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/*
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* Collect the per-cpu time buckets and average them into a
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* single time sample that is normalized to wallclock time.
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*
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* For averaging, each CPU is weighted by its non-idle time in
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* the sampling period. This eliminates artifacts from uneven
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* loading, or even entirely idle CPUs.
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*/
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for_each_possible_cpu(cpu) {
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u32 times[NR_PSI_STATES];
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u32 nonidle;
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u32 cpu_changed_states;
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get_recent_times(group, cpu, aggregator, times,
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&cpu_changed_states);
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changed_states |= cpu_changed_states;
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nonidle = nsecs_to_jiffies(times[PSI_NONIDLE]);
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nonidle_total += nonidle;
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for (s = 0; s < PSI_NONIDLE; s++)
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deltas[s] += (u64)times[s] * nonidle;
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}
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/*
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* Integrate the sample into the running statistics that are
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* reported to userspace: the cumulative stall times and the
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* decaying averages.
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*
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* Pressure percentages are sampled at PSI_FREQ. We might be
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* called more often when the user polls more frequently than
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* that; we might be called less often when there is no task
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* activity, thus no data, and clock ticks are sporadic. The
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* below handles both.
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*/
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/* total= */
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for (s = 0; s < NR_PSI_STATES - 1; s++)
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group->total[aggregator][s] +=
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div_u64(deltas[s], max(nonidle_total, 1UL));
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if (pchanged_states)
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*pchanged_states = changed_states;
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}
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static u64 update_averages(struct psi_group *group, u64 now)
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{
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unsigned long missed_periods = 0;
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u64 expires, period;
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u64 avg_next_update;
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int s;
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/* avgX= */
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expires = group->avg_next_update;
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if (now - expires >= psi_period)
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missed_periods = div_u64(now - expires, psi_period);
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/*
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* The periodic clock tick can get delayed for various
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* reasons, especially on loaded systems. To avoid clock
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* drift, we schedule the clock in fixed psi_period intervals.
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* But the deltas we sample out of the per-cpu buckets above
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* are based on the actual time elapsing between clock ticks.
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*/
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avg_next_update = expires + ((1 + missed_periods) * psi_period);
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period = now - (group->avg_last_update + (missed_periods * psi_period));
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group->avg_last_update = now;
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for (s = 0; s < NR_PSI_STATES - 1; s++) {
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u32 sample;
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sample = group->total[PSI_AVGS][s] - group->avg_total[s];
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/*
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* Due to the lockless sampling of the time buckets,
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* recorded time deltas can slip into the next period,
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* which under full pressure can result in samples in
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* excess of the period length.
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*
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* We don't want to report non-sensical pressures in
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* excess of 100%, nor do we want to drop such events
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* on the floor. Instead we punt any overage into the
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* future until pressure subsides. By doing this we
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* don't underreport the occurring pressure curve, we
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* just report it delayed by one period length.
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*
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* The error isn't cumulative. As soon as another
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* delta slips from a period P to P+1, by definition
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* it frees up its time T in P.
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*/
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if (sample > period)
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sample = period;
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group->avg_total[s] += sample;
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calc_avgs(group->avg[s], missed_periods, sample, period);
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}
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return avg_next_update;
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}
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static void psi_avgs_work(struct work_struct *work)
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{
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struct delayed_work *dwork;
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struct psi_group *group;
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u32 changed_states;
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bool nonidle;
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u64 now;
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dwork = to_delayed_work(work);
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group = container_of(dwork, struct psi_group, avgs_work);
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mutex_lock(&group->avgs_lock);
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now = sched_clock();
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collect_percpu_times(group, PSI_AVGS, &changed_states);
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nonidle = changed_states & (1 << PSI_NONIDLE);
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/*
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* If there is task activity, periodically fold the per-cpu
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* times and feed samples into the running averages. If things
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* are idle and there is no data to process, stop the clock.
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* Once restarted, we'll catch up the running averages in one
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* go - see calc_avgs() and missed_periods.
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*/
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if (now >= group->avg_next_update)
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group->avg_next_update = update_averages(group, now);
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if (nonidle) {
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schedule_delayed_work(dwork, nsecs_to_jiffies(
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group->avg_next_update - now) + 1);
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}
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mutex_unlock(&group->avgs_lock);
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}
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/* Trigger tracking window manupulations */
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static void window_reset(struct psi_window *win, u64 now, u64 value,
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u64 prev_growth)
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{
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win->start_time = now;
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win->start_value = value;
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win->prev_growth = prev_growth;
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}
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/*
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* PSI growth tracking window update and growth calculation routine.
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*
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* This approximates a sliding tracking window by interpolating
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* partially elapsed windows using historical growth data from the
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* previous intervals. This minimizes memory requirements (by not storing
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* all the intermediate values in the previous window) and simplifies
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* the calculations. It works well because PSI signal changes only in
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* positive direction and over relatively small window sizes the growth
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* is close to linear.
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*/
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static u64 window_update(struct psi_window *win, u64 now, u64 value)
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{
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u64 elapsed;
|
|
u64 growth;
|
|
|
|
elapsed = now - win->start_time;
|
|
growth = value - win->start_value;
|
|
/*
|
|
* After each tracking window passes win->start_value and
|
|
* win->start_time get reset and win->prev_growth stores
|
|
* the average per-window growth of the previous window.
|
|
* win->prev_growth is then used to interpolate additional
|
|
* growth from the previous window assuming it was linear.
|
|
*/
|
|
if (elapsed > win->size)
|
|
window_reset(win, now, value, growth);
|
|
else {
|
|
u32 remaining;
|
|
|
|
remaining = win->size - elapsed;
|
|
growth += div64_u64(win->prev_growth * remaining, win->size);
|
|
}
|
|
|
|
return growth;
|
|
}
|
|
|
|
static void init_triggers(struct psi_group *group, u64 now)
|
|
{
|
|
struct psi_trigger *t;
|
|
|
|
list_for_each_entry(t, &group->triggers, node)
|
|
window_reset(&t->win, now,
|
|
group->total[PSI_POLL][t->state], 0);
|
|
memcpy(group->polling_total, group->total[PSI_POLL],
|
|
sizeof(group->polling_total));
|
|
group->polling_next_update = now + group->poll_min_period;
|
|
}
|
|
|
|
static u64 update_triggers(struct psi_group *group, u64 now)
|
|
{
|
|
struct psi_trigger *t;
|
|
bool new_stall = false;
|
|
u64 *total = group->total[PSI_POLL];
|
|
|
|
/*
|
|
* On subsequent updates, calculate growth deltas and let
|
|
* watchers know when their specified thresholds are exceeded.
|
|
*/
|
|
list_for_each_entry(t, &group->triggers, node) {
|
|
u64 growth;
|
|
|
|
/* Check for stall activity */
|
|
if (group->polling_total[t->state] == total[t->state])
|
|
continue;
|
|
|
|
/*
|
|
* Multiple triggers might be looking at the same state,
|
|
* remember to update group->polling_total[] once we've
|
|
* been through all of them. Also remember to extend the
|
|
* polling time if we see new stall activity.
|
|
*/
|
|
new_stall = true;
|
|
|
|
/* Calculate growth since last update */
|
|
growth = window_update(&t->win, now, total[t->state]);
|
|
if (growth < t->threshold)
|
|
continue;
|
|
|
|
/* Limit event signaling to once per window */
|
|
if (now < t->last_event_time + t->win.size)
|
|
continue;
|
|
|
|
/* Generate an event */
|
|
if (cmpxchg(&t->event, 0, 1) == 0)
|
|
wake_up_interruptible(&t->event_wait);
|
|
t->last_event_time = now;
|
|
}
|
|
|
|
if (new_stall)
|
|
memcpy(group->polling_total, total,
|
|
sizeof(group->polling_total));
|
|
|
|
return now + group->poll_min_period;
|
|
}
|
|
|
|
/*
|
|
* Schedule polling if it's not already scheduled. It's safe to call even from
|
|
* hotpath because even though kthread_queue_delayed_work takes worker->lock
|
|
* spinlock that spinlock is never contended due to poll_scheduled atomic
|
|
* preventing such competition.
|
|
*/
|
|
static void psi_schedule_poll_work(struct psi_group *group, unsigned long delay)
|
|
{
|
|
struct kthread_worker *kworker;
|
|
|
|
/* Do not reschedule if already scheduled */
|
|
if (atomic_cmpxchg(&group->poll_scheduled, 0, 1) != 0)
|
|
return;
|
|
|
|
rcu_read_lock();
|
|
|
|
kworker = rcu_dereference(group->poll_kworker);
|
|
/*
|
|
* kworker might be NULL in case psi_trigger_destroy races with
|
|
* psi_task_change (hotpath) which can't use locks
|
|
*/
|
|
if (likely(kworker))
|
|
kthread_queue_delayed_work(kworker, &group->poll_work, delay);
|
|
else
|
|
atomic_set(&group->poll_scheduled, 0);
|
|
|
|
rcu_read_unlock();
|
|
}
|
|
|
|
static void psi_poll_work(struct kthread_work *work)
|
|
{
|
|
struct kthread_delayed_work *dwork;
|
|
struct psi_group *group;
|
|
u32 changed_states;
|
|
u64 now;
|
|
|
|
dwork = container_of(work, struct kthread_delayed_work, work);
|
|
group = container_of(dwork, struct psi_group, poll_work);
|
|
|
|
atomic_set(&group->poll_scheduled, 0);
|
|
|
|
mutex_lock(&group->trigger_lock);
|
|
|
|
now = sched_clock();
|
|
|
|
collect_percpu_times(group, PSI_POLL, &changed_states);
|
|
|
|
if (changed_states & group->poll_states) {
|
|
/* Initialize trigger windows when entering polling mode */
|
|
if (now > group->polling_until)
|
|
init_triggers(group, now);
|
|
|
|
/*
|
|
* Keep the monitor active for at least the duration of the
|
|
* minimum tracking window as long as monitor states are
|
|
* changing.
|
|
*/
|
|
group->polling_until = now +
|
|
group->poll_min_period * UPDATES_PER_WINDOW;
|
|
}
|
|
|
|
if (now > group->polling_until) {
|
|
group->polling_next_update = ULLONG_MAX;
|
|
goto out;
|
|
}
|
|
|
|
if (now >= group->polling_next_update)
|
|
group->polling_next_update = update_triggers(group, now);
|
|
|
|
psi_schedule_poll_work(group,
|
|
nsecs_to_jiffies(group->polling_next_update - now) + 1);
|
|
|
|
out:
|
|
mutex_unlock(&group->trigger_lock);
|
|
}
|
|
|
|
static void record_times(struct psi_group_cpu *groupc, int cpu,
|
|
bool memstall_tick)
|
|
{
|
|
u32 delta;
|
|
u64 now;
|
|
|
|
now = cpu_clock(cpu);
|
|
delta = now - groupc->state_start;
|
|
groupc->state_start = now;
|
|
|
|
if (groupc->state_mask & (1 << PSI_IO_SOME)) {
|
|
groupc->times[PSI_IO_SOME] += delta;
|
|
if (groupc->state_mask & (1 << PSI_IO_FULL))
|
|
groupc->times[PSI_IO_FULL] += delta;
|
|
}
|
|
|
|
if (groupc->state_mask & (1 << PSI_MEM_SOME)) {
|
|
groupc->times[PSI_MEM_SOME] += delta;
|
|
if (groupc->state_mask & (1 << PSI_MEM_FULL))
|
|
groupc->times[PSI_MEM_FULL] += delta;
|
|
else if (memstall_tick) {
|
|
u32 sample;
|
|
/*
|
|
* Since we care about lost potential, a
|
|
* memstall is FULL when there are no other
|
|
* working tasks, but also when the CPU is
|
|
* actively reclaiming and nothing productive
|
|
* could run even if it were runnable.
|
|
*
|
|
* When the timer tick sees a reclaiming CPU,
|
|
* regardless of runnable tasks, sample a FULL
|
|
* tick (or less if it hasn't been a full tick
|
|
* since the last state change).
|
|
*/
|
|
sample = min(delta, (u32)jiffies_to_nsecs(1));
|
|
groupc->times[PSI_MEM_FULL] += sample;
|
|
}
|
|
}
|
|
|
|
if (groupc->state_mask & (1 << PSI_CPU_SOME))
|
|
groupc->times[PSI_CPU_SOME] += delta;
|
|
|
|
if (groupc->state_mask & (1 << PSI_NONIDLE))
|
|
groupc->times[PSI_NONIDLE] += delta;
|
|
}
|
|
|
|
static void psi_group_change(struct psi_group *group, int cpu,
|
|
unsigned int clear, unsigned int set,
|
|
bool wake_clock)
|
|
{
|
|
struct psi_group_cpu *groupc;
|
|
u32 state_mask = 0;
|
|
unsigned int t, m;
|
|
enum psi_states s;
|
|
|
|
groupc = per_cpu_ptr(group->pcpu, cpu);
|
|
|
|
/*
|
|
* First we assess the aggregate resource states this CPU's
|
|
* tasks have been in since the last change, and account any
|
|
* SOME and FULL time these may have resulted in.
|
|
*
|
|
* Then we update the task counts according to the state
|
|
* change requested through the @clear and @set bits.
|
|
*/
|
|
write_seqcount_begin(&groupc->seq);
|
|
|
|
record_times(groupc, cpu, false);
|
|
|
|
for (t = 0, m = clear; m; m &= ~(1 << t), t++) {
|
|
if (!(m & (1 << t)))
|
|
continue;
|
|
if (groupc->tasks[t] == 0 && !psi_bug) {
|
|
printk_deferred(KERN_ERR "psi: task underflow! cpu=%d t=%d tasks=[%u %u %u %u] clear=%x set=%x\n",
|
|
cpu, t, groupc->tasks[0],
|
|
groupc->tasks[1], groupc->tasks[2],
|
|
groupc->tasks[3], clear, set);
|
|
psi_bug = 1;
|
|
}
|
|
groupc->tasks[t]--;
|
|
}
|
|
|
|
for (t = 0; set; set &= ~(1 << t), t++)
|
|
if (set & (1 << t))
|
|
groupc->tasks[t]++;
|
|
|
|
/* Calculate state mask representing active states */
|
|
for (s = 0; s < NR_PSI_STATES; s++) {
|
|
if (test_state(groupc->tasks, s))
|
|
state_mask |= (1 << s);
|
|
}
|
|
groupc->state_mask = state_mask;
|
|
|
|
write_seqcount_end(&groupc->seq);
|
|
|
|
if (state_mask & group->poll_states)
|
|
psi_schedule_poll_work(group, 1);
|
|
|
|
if (wake_clock && !delayed_work_pending(&group->avgs_work))
|
|
schedule_delayed_work(&group->avgs_work, PSI_FREQ);
|
|
}
|
|
|
|
static struct psi_group *iterate_groups(struct task_struct *task, void **iter)
|
|
{
|
|
#ifdef CONFIG_CGROUPS
|
|
struct cgroup *cgroup = NULL;
|
|
|
|
if (!*iter)
|
|
cgroup = task->cgroups->dfl_cgrp;
|
|
else if (*iter == &psi_system)
|
|
return NULL;
|
|
else
|
|
cgroup = cgroup_parent(*iter);
|
|
|
|
if (cgroup && cgroup_parent(cgroup)) {
|
|
*iter = cgroup;
|
|
return cgroup_psi(cgroup);
|
|
}
|
|
#else
|
|
if (*iter)
|
|
return NULL;
|
|
#endif
|
|
*iter = &psi_system;
|
|
return &psi_system;
|
|
}
|
|
|
|
static void psi_flags_change(struct task_struct *task, int clear, int set)
|
|
{
|
|
if (((task->psi_flags & set) ||
|
|
(task->psi_flags & clear) != clear) &&
|
|
!psi_bug) {
|
|
printk_deferred(KERN_ERR "psi: inconsistent task state! task=%d:%s cpu=%d psi_flags=%x clear=%x set=%x\n",
|
|
task->pid, task->comm, task_cpu(task),
|
|
task->psi_flags, clear, set);
|
|
psi_bug = 1;
|
|
}
|
|
|
|
task->psi_flags &= ~clear;
|
|
task->psi_flags |= set;
|
|
}
|
|
|
|
void psi_task_change(struct task_struct *task, int clear, int set)
|
|
{
|
|
int cpu = task_cpu(task);
|
|
struct psi_group *group;
|
|
bool wake_clock = true;
|
|
void *iter = NULL;
|
|
|
|
if (!task->pid)
|
|
return;
|
|
|
|
psi_flags_change(task, clear, set);
|
|
|
|
/*
|
|
* Periodic aggregation shuts off if there is a period of no
|
|
* task changes, so we wake it back up if necessary. However,
|
|
* don't do this if the task change is the aggregation worker
|
|
* itself going to sleep, or we'll ping-pong forever.
|
|
*/
|
|
if (unlikely((clear & TSK_RUNNING) &&
|
|
(task->flags & PF_WQ_WORKER) &&
|
|
wq_worker_last_func(task) == psi_avgs_work))
|
|
wake_clock = false;
|
|
|
|
while ((group = iterate_groups(task, &iter)))
|
|
psi_group_change(group, cpu, clear, set, wake_clock);
|
|
}
|
|
|
|
void psi_task_switch(struct task_struct *prev, struct task_struct *next,
|
|
bool sleep)
|
|
{
|
|
struct psi_group *group, *common = NULL;
|
|
int cpu = task_cpu(prev);
|
|
void *iter;
|
|
|
|
if (next->pid) {
|
|
psi_flags_change(next, 0, TSK_ONCPU);
|
|
/*
|
|
* When moving state between tasks, the group that
|
|
* contains them both does not change: we can stop
|
|
* updating the tree once we reach the first common
|
|
* ancestor. Iterate @next's ancestors until we
|
|
* encounter @prev's state.
|
|
*/
|
|
iter = NULL;
|
|
while ((group = iterate_groups(next, &iter))) {
|
|
if (per_cpu_ptr(group->pcpu, cpu)->tasks[NR_ONCPU]) {
|
|
common = group;
|
|
break;
|
|
}
|
|
|
|
psi_group_change(group, cpu, 0, TSK_ONCPU, true);
|
|
}
|
|
}
|
|
|
|
/*
|
|
* If this is a voluntary sleep, dequeue will have taken care
|
|
* of the outgoing TSK_ONCPU alongside TSK_RUNNING already. We
|
|
* only need to deal with it during preemption.
|
|
*/
|
|
if (sleep)
|
|
return;
|
|
|
|
if (prev->pid) {
|
|
psi_flags_change(prev, TSK_ONCPU, 0);
|
|
|
|
iter = NULL;
|
|
while ((group = iterate_groups(prev, &iter)) && group != common)
|
|
psi_group_change(group, cpu, TSK_ONCPU, 0, true);
|
|
}
|
|
}
|
|
|
|
void psi_memstall_tick(struct task_struct *task, int cpu)
|
|
{
|
|
struct psi_group *group;
|
|
void *iter = NULL;
|
|
|
|
while ((group = iterate_groups(task, &iter))) {
|
|
struct psi_group_cpu *groupc;
|
|
|
|
groupc = per_cpu_ptr(group->pcpu, cpu);
|
|
write_seqcount_begin(&groupc->seq);
|
|
record_times(groupc, cpu, true);
|
|
write_seqcount_end(&groupc->seq);
|
|
}
|
|
}
|
|
|
|
/**
|
|
* psi_memstall_enter - mark the beginning of a memory stall section
|
|
* @flags: flags to handle nested sections
|
|
*
|
|
* Marks the calling task as being stalled due to a lack of memory,
|
|
* such as waiting for a refault or performing reclaim.
|
|
*/
|
|
void psi_memstall_enter(unsigned long *flags)
|
|
{
|
|
struct rq_flags rf;
|
|
struct rq *rq;
|
|
|
|
if (static_branch_likely(&psi_disabled))
|
|
return;
|
|
|
|
*flags = current->in_memstall;
|
|
if (*flags)
|
|
return;
|
|
/*
|
|
* in_memstall setting & accounting needs to be atomic wrt
|
|
* changes to the task's scheduling state, otherwise we can
|
|
* race with CPU migration.
|
|
*/
|
|
rq = this_rq_lock_irq(&rf);
|
|
|
|
current->in_memstall = 1;
|
|
psi_task_change(current, 0, TSK_MEMSTALL);
|
|
|
|
rq_unlock_irq(rq, &rf);
|
|
}
|
|
|
|
/**
|
|
* psi_memstall_leave - mark the end of an memory stall section
|
|
* @flags: flags to handle nested memdelay sections
|
|
*
|
|
* Marks the calling task as no longer stalled due to lack of memory.
|
|
*/
|
|
void psi_memstall_leave(unsigned long *flags)
|
|
{
|
|
struct rq_flags rf;
|
|
struct rq *rq;
|
|
|
|
if (static_branch_likely(&psi_disabled))
|
|
return;
|
|
|
|
if (*flags)
|
|
return;
|
|
/*
|
|
* in_memstall clearing & accounting needs to be atomic wrt
|
|
* changes to the task's scheduling state, otherwise we could
|
|
* race with CPU migration.
|
|
*/
|
|
rq = this_rq_lock_irq(&rf);
|
|
|
|
current->in_memstall = 0;
|
|
psi_task_change(current, TSK_MEMSTALL, 0);
|
|
|
|
rq_unlock_irq(rq, &rf);
|
|
}
|
|
|
|
#ifdef CONFIG_CGROUPS
|
|
int psi_cgroup_alloc(struct cgroup *cgroup)
|
|
{
|
|
if (static_branch_likely(&psi_disabled))
|
|
return 0;
|
|
|
|
cgroup->psi.pcpu = alloc_percpu(struct psi_group_cpu);
|
|
if (!cgroup->psi.pcpu)
|
|
return -ENOMEM;
|
|
group_init(&cgroup->psi);
|
|
return 0;
|
|
}
|
|
|
|
void psi_cgroup_free(struct cgroup *cgroup)
|
|
{
|
|
if (static_branch_likely(&psi_disabled))
|
|
return;
|
|
|
|
cancel_delayed_work_sync(&cgroup->psi.avgs_work);
|
|
free_percpu(cgroup->psi.pcpu);
|
|
/* All triggers must be removed by now */
|
|
WARN_ONCE(cgroup->psi.poll_states, "psi: trigger leak\n");
|
|
}
|
|
|
|
/**
|
|
* cgroup_move_task - move task to a different cgroup
|
|
* @task: the task
|
|
* @to: the target css_set
|
|
*
|
|
* Move task to a new cgroup and safely migrate its associated stall
|
|
* state between the different groups.
|
|
*
|
|
* This function acquires the task's rq lock to lock out concurrent
|
|
* changes to the task's scheduling state and - in case the task is
|
|
* running - concurrent changes to its stall state.
|
|
*/
|
|
void cgroup_move_task(struct task_struct *task, struct css_set *to)
|
|
{
|
|
unsigned int task_flags = 0;
|
|
struct rq_flags rf;
|
|
struct rq *rq;
|
|
|
|
if (static_branch_likely(&psi_disabled)) {
|
|
/*
|
|
* Lame to do this here, but the scheduler cannot be locked
|
|
* from the outside, so we move cgroups from inside sched/.
|
|
*/
|
|
rcu_assign_pointer(task->cgroups, to);
|
|
return;
|
|
}
|
|
|
|
rq = task_rq_lock(task, &rf);
|
|
|
|
if (task_on_rq_queued(task)) {
|
|
task_flags = TSK_RUNNING;
|
|
if (task_current(rq, task))
|
|
task_flags |= TSK_ONCPU;
|
|
} else if (task->in_iowait)
|
|
task_flags = TSK_IOWAIT;
|
|
|
|
if (task->in_memstall)
|
|
task_flags |= TSK_MEMSTALL;
|
|
|
|
if (task_flags)
|
|
psi_task_change(task, task_flags, 0);
|
|
|
|
/* See comment above */
|
|
rcu_assign_pointer(task->cgroups, to);
|
|
|
|
if (task_flags)
|
|
psi_task_change(task, 0, task_flags);
|
|
|
|
task_rq_unlock(rq, task, &rf);
|
|
}
|
|
#endif /* CONFIG_CGROUPS */
|
|
|
|
int psi_show(struct seq_file *m, struct psi_group *group, enum psi_res res)
|
|
{
|
|
int full;
|
|
u64 now;
|
|
|
|
if (static_branch_likely(&psi_disabled))
|
|
return -EOPNOTSUPP;
|
|
|
|
/* Update averages before reporting them */
|
|
mutex_lock(&group->avgs_lock);
|
|
now = sched_clock();
|
|
collect_percpu_times(group, PSI_AVGS, NULL);
|
|
if (now >= group->avg_next_update)
|
|
group->avg_next_update = update_averages(group, now);
|
|
mutex_unlock(&group->avgs_lock);
|
|
|
|
for (full = 0; full < 2 - (res == PSI_CPU); full++) {
|
|
unsigned long avg[3];
|
|
u64 total;
|
|
int w;
|
|
|
|
for (w = 0; w < 3; w++)
|
|
avg[w] = group->avg[res * 2 + full][w];
|
|
total = div_u64(group->total[PSI_AVGS][res * 2 + full],
|
|
NSEC_PER_USEC);
|
|
|
|
seq_printf(m, "%s avg10=%lu.%02lu avg60=%lu.%02lu avg300=%lu.%02lu total=%llu\n",
|
|
full ? "full" : "some",
|
|
LOAD_INT(avg[0]), LOAD_FRAC(avg[0]),
|
|
LOAD_INT(avg[1]), LOAD_FRAC(avg[1]),
|
|
LOAD_INT(avg[2]), LOAD_FRAC(avg[2]),
|
|
total);
|
|
}
|
|
|
|
return 0;
|
|
}
|
|
|
|
static int psi_io_show(struct seq_file *m, void *v)
|
|
{
|
|
return psi_show(m, &psi_system, PSI_IO);
|
|
}
|
|
|
|
static int psi_memory_show(struct seq_file *m, void *v)
|
|
{
|
|
return psi_show(m, &psi_system, PSI_MEM);
|
|
}
|
|
|
|
static int psi_cpu_show(struct seq_file *m, void *v)
|
|
{
|
|
return psi_show(m, &psi_system, PSI_CPU);
|
|
}
|
|
|
|
static int psi_io_open(struct inode *inode, struct file *file)
|
|
{
|
|
return single_open(file, psi_io_show, NULL);
|
|
}
|
|
|
|
static int psi_memory_open(struct inode *inode, struct file *file)
|
|
{
|
|
return single_open(file, psi_memory_show, NULL);
|
|
}
|
|
|
|
static int psi_cpu_open(struct inode *inode, struct file *file)
|
|
{
|
|
return single_open(file, psi_cpu_show, NULL);
|
|
}
|
|
|
|
struct psi_trigger *psi_trigger_create(struct psi_group *group,
|
|
char *buf, size_t nbytes, enum psi_res res)
|
|
{
|
|
struct psi_trigger *t;
|
|
enum psi_states state;
|
|
u32 threshold_us;
|
|
u32 window_us;
|
|
|
|
if (static_branch_likely(&psi_disabled))
|
|
return ERR_PTR(-EOPNOTSUPP);
|
|
|
|
if (sscanf(buf, "some %u %u", &threshold_us, &window_us) == 2)
|
|
state = PSI_IO_SOME + res * 2;
|
|
else if (sscanf(buf, "full %u %u", &threshold_us, &window_us) == 2)
|
|
state = PSI_IO_FULL + res * 2;
|
|
else
|
|
return ERR_PTR(-EINVAL);
|
|
|
|
if (state >= PSI_NONIDLE)
|
|
return ERR_PTR(-EINVAL);
|
|
|
|
if (window_us < WINDOW_MIN_US ||
|
|
window_us > WINDOW_MAX_US)
|
|
return ERR_PTR(-EINVAL);
|
|
|
|
/* Check threshold */
|
|
if (threshold_us == 0 || threshold_us > window_us)
|
|
return ERR_PTR(-EINVAL);
|
|
|
|
t = kmalloc(sizeof(*t), GFP_KERNEL);
|
|
if (!t)
|
|
return ERR_PTR(-ENOMEM);
|
|
|
|
t->group = group;
|
|
t->state = state;
|
|
t->threshold = threshold_us * NSEC_PER_USEC;
|
|
t->win.size = window_us * NSEC_PER_USEC;
|
|
window_reset(&t->win, 0, 0, 0);
|
|
|
|
t->event = 0;
|
|
t->last_event_time = 0;
|
|
init_waitqueue_head(&t->event_wait);
|
|
kref_init(&t->refcount);
|
|
|
|
mutex_lock(&group->trigger_lock);
|
|
|
|
if (!rcu_access_pointer(group->poll_kworker)) {
|
|
struct sched_param param = {
|
|
.sched_priority = 1,
|
|
};
|
|
struct kthread_worker *kworker;
|
|
|
|
kworker = kthread_create_worker(0, "psimon");
|
|
if (IS_ERR(kworker)) {
|
|
kfree(t);
|
|
mutex_unlock(&group->trigger_lock);
|
|
return ERR_CAST(kworker);
|
|
}
|
|
sched_setscheduler_nocheck(kworker->task, SCHED_FIFO, ¶m);
|
|
kthread_init_delayed_work(&group->poll_work,
|
|
psi_poll_work);
|
|
rcu_assign_pointer(group->poll_kworker, kworker);
|
|
}
|
|
|
|
list_add(&t->node, &group->triggers);
|
|
group->poll_min_period = min(group->poll_min_period,
|
|
div_u64(t->win.size, UPDATES_PER_WINDOW));
|
|
group->nr_triggers[t->state]++;
|
|
group->poll_states |= (1 << t->state);
|
|
|
|
mutex_unlock(&group->trigger_lock);
|
|
|
|
return t;
|
|
}
|
|
|
|
static void psi_trigger_destroy(struct kref *ref)
|
|
{
|
|
struct psi_trigger *t = container_of(ref, struct psi_trigger, refcount);
|
|
struct psi_group *group = t->group;
|
|
struct kthread_worker *kworker_to_destroy = NULL;
|
|
|
|
if (static_branch_likely(&psi_disabled))
|
|
return;
|
|
|
|
/*
|
|
* Wakeup waiters to stop polling. Can happen if cgroup is deleted
|
|
* from under a polling process.
|
|
*/
|
|
wake_up_interruptible(&t->event_wait);
|
|
|
|
mutex_lock(&group->trigger_lock);
|
|
|
|
if (!list_empty(&t->node)) {
|
|
struct psi_trigger *tmp;
|
|
u64 period = ULLONG_MAX;
|
|
|
|
list_del(&t->node);
|
|
group->nr_triggers[t->state]--;
|
|
if (!group->nr_triggers[t->state])
|
|
group->poll_states &= ~(1 << t->state);
|
|
/* reset min update period for the remaining triggers */
|
|
list_for_each_entry(tmp, &group->triggers, node)
|
|
period = min(period, div_u64(tmp->win.size,
|
|
UPDATES_PER_WINDOW));
|
|
group->poll_min_period = period;
|
|
/* Destroy poll_kworker when the last trigger is destroyed */
|
|
if (group->poll_states == 0) {
|
|
group->polling_until = 0;
|
|
kworker_to_destroy = rcu_dereference_protected(
|
|
group->poll_kworker,
|
|
lockdep_is_held(&group->trigger_lock));
|
|
rcu_assign_pointer(group->poll_kworker, NULL);
|
|
}
|
|
}
|
|
|
|
mutex_unlock(&group->trigger_lock);
|
|
|
|
/*
|
|
* Wait for both *trigger_ptr from psi_trigger_replace and
|
|
* poll_kworker RCUs to complete their read-side critical sections
|
|
* before destroying the trigger and optionally the poll_kworker
|
|
*/
|
|
synchronize_rcu();
|
|
/*
|
|
* Destroy the kworker after releasing trigger_lock to prevent a
|
|
* deadlock while waiting for psi_poll_work to acquire trigger_lock
|
|
*/
|
|
if (kworker_to_destroy) {
|
|
/*
|
|
* After the RCU grace period has expired, the worker
|
|
* can no longer be found through group->poll_kworker.
|
|
* But it might have been already scheduled before
|
|
* that - deschedule it cleanly before destroying it.
|
|
*/
|
|
kthread_cancel_delayed_work_sync(&group->poll_work);
|
|
atomic_set(&group->poll_scheduled, 0);
|
|
|
|
kthread_destroy_worker(kworker_to_destroy);
|
|
}
|
|
kfree(t);
|
|
}
|
|
|
|
void psi_trigger_replace(void **trigger_ptr, struct psi_trigger *new)
|
|
{
|
|
struct psi_trigger *old = *trigger_ptr;
|
|
|
|
if (static_branch_likely(&psi_disabled))
|
|
return;
|
|
|
|
rcu_assign_pointer(*trigger_ptr, new);
|
|
if (old)
|
|
kref_put(&old->refcount, psi_trigger_destroy);
|
|
}
|
|
|
|
__poll_t psi_trigger_poll(void **trigger_ptr,
|
|
struct file *file, poll_table *wait)
|
|
{
|
|
__poll_t ret = DEFAULT_POLLMASK;
|
|
struct psi_trigger *t;
|
|
|
|
if (static_branch_likely(&psi_disabled))
|
|
return DEFAULT_POLLMASK | EPOLLERR | EPOLLPRI;
|
|
|
|
rcu_read_lock();
|
|
|
|
t = rcu_dereference(*(void __rcu __force **)trigger_ptr);
|
|
if (!t) {
|
|
rcu_read_unlock();
|
|
return DEFAULT_POLLMASK | EPOLLERR | EPOLLPRI;
|
|
}
|
|
kref_get(&t->refcount);
|
|
|
|
rcu_read_unlock();
|
|
|
|
poll_wait(file, &t->event_wait, wait);
|
|
|
|
if (cmpxchg(&t->event, 1, 0) == 1)
|
|
ret |= EPOLLPRI;
|
|
|
|
kref_put(&t->refcount, psi_trigger_destroy);
|
|
|
|
return ret;
|
|
}
|
|
|
|
static ssize_t psi_write(struct file *file, const char __user *user_buf,
|
|
size_t nbytes, enum psi_res res)
|
|
{
|
|
char buf[32];
|
|
size_t buf_size;
|
|
struct seq_file *seq;
|
|
struct psi_trigger *new;
|
|
|
|
if (static_branch_likely(&psi_disabled))
|
|
return -EOPNOTSUPP;
|
|
|
|
if (!nbytes)
|
|
return -EINVAL;
|
|
|
|
buf_size = min(nbytes, sizeof(buf));
|
|
if (copy_from_user(buf, user_buf, buf_size))
|
|
return -EFAULT;
|
|
|
|
buf[buf_size - 1] = '\0';
|
|
|
|
new = psi_trigger_create(&psi_system, buf, nbytes, res);
|
|
if (IS_ERR(new))
|
|
return PTR_ERR(new);
|
|
|
|
seq = file->private_data;
|
|
/* Take seq->lock to protect seq->private from concurrent writes */
|
|
mutex_lock(&seq->lock);
|
|
psi_trigger_replace(&seq->private, new);
|
|
mutex_unlock(&seq->lock);
|
|
|
|
return nbytes;
|
|
}
|
|
|
|
static ssize_t psi_io_write(struct file *file, const char __user *user_buf,
|
|
size_t nbytes, loff_t *ppos)
|
|
{
|
|
return psi_write(file, user_buf, nbytes, PSI_IO);
|
|
}
|
|
|
|
static ssize_t psi_memory_write(struct file *file, const char __user *user_buf,
|
|
size_t nbytes, loff_t *ppos)
|
|
{
|
|
return psi_write(file, user_buf, nbytes, PSI_MEM);
|
|
}
|
|
|
|
static ssize_t psi_cpu_write(struct file *file, const char __user *user_buf,
|
|
size_t nbytes, loff_t *ppos)
|
|
{
|
|
return psi_write(file, user_buf, nbytes, PSI_CPU);
|
|
}
|
|
|
|
static __poll_t psi_fop_poll(struct file *file, poll_table *wait)
|
|
{
|
|
struct seq_file *seq = file->private_data;
|
|
|
|
return psi_trigger_poll(&seq->private, file, wait);
|
|
}
|
|
|
|
static int psi_fop_release(struct inode *inode, struct file *file)
|
|
{
|
|
struct seq_file *seq = file->private_data;
|
|
|
|
psi_trigger_replace(&seq->private, NULL);
|
|
return single_release(inode, file);
|
|
}
|
|
|
|
static const struct proc_ops psi_io_proc_ops = {
|
|
.proc_open = psi_io_open,
|
|
.proc_read = seq_read,
|
|
.proc_lseek = seq_lseek,
|
|
.proc_write = psi_io_write,
|
|
.proc_poll = psi_fop_poll,
|
|
.proc_release = psi_fop_release,
|
|
};
|
|
|
|
static const struct proc_ops psi_memory_proc_ops = {
|
|
.proc_open = psi_memory_open,
|
|
.proc_read = seq_read,
|
|
.proc_lseek = seq_lseek,
|
|
.proc_write = psi_memory_write,
|
|
.proc_poll = psi_fop_poll,
|
|
.proc_release = psi_fop_release,
|
|
};
|
|
|
|
static const struct proc_ops psi_cpu_proc_ops = {
|
|
.proc_open = psi_cpu_open,
|
|
.proc_read = seq_read,
|
|
.proc_lseek = seq_lseek,
|
|
.proc_write = psi_cpu_write,
|
|
.proc_poll = psi_fop_poll,
|
|
.proc_release = psi_fop_release,
|
|
};
|
|
|
|
static int __init psi_proc_init(void)
|
|
{
|
|
if (psi_enable) {
|
|
proc_mkdir("pressure", NULL);
|
|
proc_create("pressure/io", 0, NULL, &psi_io_proc_ops);
|
|
proc_create("pressure/memory", 0, NULL, &psi_memory_proc_ops);
|
|
proc_create("pressure/cpu", 0, NULL, &psi_cpu_proc_ops);
|
|
}
|
|
return 0;
|
|
}
|
|
module_init(psi_proc_init);
|