![Bart Van Assche](/assets/img/avatar_default.png)
No code that occurs between blk_mq_get_ctx() and blk_mq_put_ctx() depends on preemption being disabled for its correctness. Since removing the CPU preemption calls does not measurably affect performance, simplify the blk-mq code by removing the blk_mq_put_ctx() function and also by not disabling preemption in blk_mq_get_ctx(). Cc: Hannes Reinecke <hare@suse.com> Cc: Omar Sandoval <osandov@fb.com> Reviewed-by: Christoph Hellwig <hch@lst.de> Reviewed-by: Ming Lei <ming.lei@redhat.com> Signed-off-by: Bart Van Assche <bvanassche@acm.org> Signed-off-by: Jens Axboe <axboe@kernel.dk>
584 lines
14 KiB
C
584 lines
14 KiB
C
// SPDX-License-Identifier: GPL-2.0
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/*
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* blk-mq scheduling framework
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*
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* Copyright (C) 2016 Jens Axboe
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*/
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#include <linux/kernel.h>
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#include <linux/module.h>
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#include <linux/blk-mq.h>
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#include <trace/events/block.h>
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#include "blk.h"
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#include "blk-mq.h"
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#include "blk-mq-debugfs.h"
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#include "blk-mq-sched.h"
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#include "blk-mq-tag.h"
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#include "blk-wbt.h"
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void blk_mq_sched_free_hctx_data(struct request_queue *q,
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void (*exit)(struct blk_mq_hw_ctx *))
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{
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struct blk_mq_hw_ctx *hctx;
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int i;
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queue_for_each_hw_ctx(q, hctx, i) {
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if (exit && hctx->sched_data)
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exit(hctx);
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kfree(hctx->sched_data);
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hctx->sched_data = NULL;
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}
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}
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EXPORT_SYMBOL_GPL(blk_mq_sched_free_hctx_data);
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void blk_mq_sched_assign_ioc(struct request *rq)
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{
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struct request_queue *q = rq->q;
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struct io_context *ioc;
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struct io_cq *icq;
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/*
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* May not have an IO context if it's a passthrough request
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*/
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ioc = current->io_context;
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if (!ioc)
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return;
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spin_lock_irq(&q->queue_lock);
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icq = ioc_lookup_icq(ioc, q);
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spin_unlock_irq(&q->queue_lock);
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if (!icq) {
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icq = ioc_create_icq(ioc, q, GFP_ATOMIC);
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if (!icq)
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return;
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}
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get_io_context(icq->ioc);
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rq->elv.icq = icq;
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}
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/*
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* Mark a hardware queue as needing a restart. For shared queues, maintain
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* a count of how many hardware queues are marked for restart.
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*/
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void blk_mq_sched_mark_restart_hctx(struct blk_mq_hw_ctx *hctx)
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{
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if (test_bit(BLK_MQ_S_SCHED_RESTART, &hctx->state))
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return;
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set_bit(BLK_MQ_S_SCHED_RESTART, &hctx->state);
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}
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EXPORT_SYMBOL_GPL(blk_mq_sched_mark_restart_hctx);
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void blk_mq_sched_restart(struct blk_mq_hw_ctx *hctx)
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{
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if (!test_bit(BLK_MQ_S_SCHED_RESTART, &hctx->state))
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return;
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clear_bit(BLK_MQ_S_SCHED_RESTART, &hctx->state);
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blk_mq_run_hw_queue(hctx, true);
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}
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/*
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* Only SCSI implements .get_budget and .put_budget, and SCSI restarts
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* its queue by itself in its completion handler, so we don't need to
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* restart queue if .get_budget() returns BLK_STS_NO_RESOURCE.
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*/
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static void blk_mq_do_dispatch_sched(struct blk_mq_hw_ctx *hctx)
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{
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struct request_queue *q = hctx->queue;
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struct elevator_queue *e = q->elevator;
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LIST_HEAD(rq_list);
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do {
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struct request *rq;
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if (e->type->ops.has_work && !e->type->ops.has_work(hctx))
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break;
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if (!blk_mq_get_dispatch_budget(hctx))
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break;
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rq = e->type->ops.dispatch_request(hctx);
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if (!rq) {
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blk_mq_put_dispatch_budget(hctx);
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break;
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}
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/*
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* Now this rq owns the budget which has to be released
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* if this rq won't be queued to driver via .queue_rq()
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* in blk_mq_dispatch_rq_list().
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*/
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list_add(&rq->queuelist, &rq_list);
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} while (blk_mq_dispatch_rq_list(q, &rq_list, true));
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}
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static struct blk_mq_ctx *blk_mq_next_ctx(struct blk_mq_hw_ctx *hctx,
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struct blk_mq_ctx *ctx)
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{
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unsigned short idx = ctx->index_hw[hctx->type];
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if (++idx == hctx->nr_ctx)
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idx = 0;
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return hctx->ctxs[idx];
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}
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/*
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* Only SCSI implements .get_budget and .put_budget, and SCSI restarts
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* its queue by itself in its completion handler, so we don't need to
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* restart queue if .get_budget() returns BLK_STS_NO_RESOURCE.
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*/
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static void blk_mq_do_dispatch_ctx(struct blk_mq_hw_ctx *hctx)
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{
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struct request_queue *q = hctx->queue;
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LIST_HEAD(rq_list);
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struct blk_mq_ctx *ctx = READ_ONCE(hctx->dispatch_from);
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do {
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struct request *rq;
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if (!sbitmap_any_bit_set(&hctx->ctx_map))
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break;
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if (!blk_mq_get_dispatch_budget(hctx))
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break;
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rq = blk_mq_dequeue_from_ctx(hctx, ctx);
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if (!rq) {
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blk_mq_put_dispatch_budget(hctx);
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break;
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}
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/*
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* Now this rq owns the budget which has to be released
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* if this rq won't be queued to driver via .queue_rq()
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* in blk_mq_dispatch_rq_list().
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*/
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list_add(&rq->queuelist, &rq_list);
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/* round robin for fair dispatch */
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ctx = blk_mq_next_ctx(hctx, rq->mq_ctx);
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} while (blk_mq_dispatch_rq_list(q, &rq_list, true));
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WRITE_ONCE(hctx->dispatch_from, ctx);
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}
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void blk_mq_sched_dispatch_requests(struct blk_mq_hw_ctx *hctx)
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{
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struct request_queue *q = hctx->queue;
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struct elevator_queue *e = q->elevator;
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const bool has_sched_dispatch = e && e->type->ops.dispatch_request;
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LIST_HEAD(rq_list);
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/* RCU or SRCU read lock is needed before checking quiesced flag */
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if (unlikely(blk_mq_hctx_stopped(hctx) || blk_queue_quiesced(q)))
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return;
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hctx->run++;
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/*
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* If we have previous entries on our dispatch list, grab them first for
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* more fair dispatch.
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*/
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if (!list_empty_careful(&hctx->dispatch)) {
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spin_lock(&hctx->lock);
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if (!list_empty(&hctx->dispatch))
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list_splice_init(&hctx->dispatch, &rq_list);
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spin_unlock(&hctx->lock);
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}
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/*
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* Only ask the scheduler for requests, if we didn't have residual
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* requests from the dispatch list. This is to avoid the case where
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* we only ever dispatch a fraction of the requests available because
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* of low device queue depth. Once we pull requests out of the IO
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* scheduler, we can no longer merge or sort them. So it's best to
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* leave them there for as long as we can. Mark the hw queue as
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* needing a restart in that case.
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*
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* We want to dispatch from the scheduler if there was nothing
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* on the dispatch list or we were able to dispatch from the
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* dispatch list.
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*/
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if (!list_empty(&rq_list)) {
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blk_mq_sched_mark_restart_hctx(hctx);
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if (blk_mq_dispatch_rq_list(q, &rq_list, false)) {
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if (has_sched_dispatch)
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blk_mq_do_dispatch_sched(hctx);
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else
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blk_mq_do_dispatch_ctx(hctx);
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}
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} else if (has_sched_dispatch) {
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blk_mq_do_dispatch_sched(hctx);
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} else if (hctx->dispatch_busy) {
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/* dequeue request one by one from sw queue if queue is busy */
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blk_mq_do_dispatch_ctx(hctx);
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} else {
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blk_mq_flush_busy_ctxs(hctx, &rq_list);
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blk_mq_dispatch_rq_list(q, &rq_list, false);
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}
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}
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bool blk_mq_sched_try_merge(struct request_queue *q, struct bio *bio,
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unsigned int nr_segs, struct request **merged_request)
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{
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struct request *rq;
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switch (elv_merge(q, &rq, bio)) {
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case ELEVATOR_BACK_MERGE:
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if (!blk_mq_sched_allow_merge(q, rq, bio))
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return false;
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if (!bio_attempt_back_merge(rq, bio, nr_segs))
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return false;
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*merged_request = attempt_back_merge(q, rq);
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if (!*merged_request)
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elv_merged_request(q, rq, ELEVATOR_BACK_MERGE);
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return true;
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case ELEVATOR_FRONT_MERGE:
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if (!blk_mq_sched_allow_merge(q, rq, bio))
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return false;
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if (!bio_attempt_front_merge(rq, bio, nr_segs))
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return false;
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*merged_request = attempt_front_merge(q, rq);
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if (!*merged_request)
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elv_merged_request(q, rq, ELEVATOR_FRONT_MERGE);
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return true;
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case ELEVATOR_DISCARD_MERGE:
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return bio_attempt_discard_merge(q, rq, bio);
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default:
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return false;
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}
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}
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EXPORT_SYMBOL_GPL(blk_mq_sched_try_merge);
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/*
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* Iterate list of requests and see if we can merge this bio with any
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* of them.
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*/
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bool blk_mq_bio_list_merge(struct request_queue *q, struct list_head *list,
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struct bio *bio, unsigned int nr_segs)
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{
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struct request *rq;
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int checked = 8;
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list_for_each_entry_reverse(rq, list, queuelist) {
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bool merged = false;
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if (!checked--)
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break;
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if (!blk_rq_merge_ok(rq, bio))
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continue;
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switch (blk_try_merge(rq, bio)) {
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case ELEVATOR_BACK_MERGE:
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if (blk_mq_sched_allow_merge(q, rq, bio))
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merged = bio_attempt_back_merge(rq, bio,
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nr_segs);
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break;
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case ELEVATOR_FRONT_MERGE:
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if (blk_mq_sched_allow_merge(q, rq, bio))
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merged = bio_attempt_front_merge(rq, bio,
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nr_segs);
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break;
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case ELEVATOR_DISCARD_MERGE:
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merged = bio_attempt_discard_merge(q, rq, bio);
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break;
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default:
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continue;
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}
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return merged;
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}
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return false;
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}
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EXPORT_SYMBOL_GPL(blk_mq_bio_list_merge);
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/*
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* Reverse check our software queue for entries that we could potentially
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* merge with. Currently includes a hand-wavy stop count of 8, to not spend
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* too much time checking for merges.
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*/
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static bool blk_mq_attempt_merge(struct request_queue *q,
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struct blk_mq_hw_ctx *hctx,
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struct blk_mq_ctx *ctx, struct bio *bio,
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unsigned int nr_segs)
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{
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enum hctx_type type = hctx->type;
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lockdep_assert_held(&ctx->lock);
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if (blk_mq_bio_list_merge(q, &ctx->rq_lists[type], bio, nr_segs)) {
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ctx->rq_merged++;
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return true;
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}
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return false;
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}
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bool __blk_mq_sched_bio_merge(struct request_queue *q, struct bio *bio,
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unsigned int nr_segs)
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{
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struct elevator_queue *e = q->elevator;
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struct blk_mq_ctx *ctx = blk_mq_get_ctx(q);
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struct blk_mq_hw_ctx *hctx = blk_mq_map_queue(q, bio->bi_opf, ctx);
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bool ret = false;
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enum hctx_type type;
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if (e && e->type->ops.bio_merge)
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return e->type->ops.bio_merge(hctx, bio, nr_segs);
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type = hctx->type;
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if ((hctx->flags & BLK_MQ_F_SHOULD_MERGE) &&
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!list_empty_careful(&ctx->rq_lists[type])) {
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/* default per sw-queue merge */
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spin_lock(&ctx->lock);
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ret = blk_mq_attempt_merge(q, hctx, ctx, bio, nr_segs);
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spin_unlock(&ctx->lock);
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}
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return ret;
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}
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bool blk_mq_sched_try_insert_merge(struct request_queue *q, struct request *rq)
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{
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return rq_mergeable(rq) && elv_attempt_insert_merge(q, rq);
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}
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EXPORT_SYMBOL_GPL(blk_mq_sched_try_insert_merge);
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void blk_mq_sched_request_inserted(struct request *rq)
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{
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trace_block_rq_insert(rq->q, rq);
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}
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EXPORT_SYMBOL_GPL(blk_mq_sched_request_inserted);
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static bool blk_mq_sched_bypass_insert(struct blk_mq_hw_ctx *hctx,
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bool has_sched,
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struct request *rq)
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{
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/* dispatch flush rq directly */
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if (rq->rq_flags & RQF_FLUSH_SEQ) {
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spin_lock(&hctx->lock);
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list_add(&rq->queuelist, &hctx->dispatch);
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spin_unlock(&hctx->lock);
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return true;
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}
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if (has_sched)
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rq->rq_flags |= RQF_SORTED;
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return false;
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}
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void blk_mq_sched_insert_request(struct request *rq, bool at_head,
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bool run_queue, bool async)
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{
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struct request_queue *q = rq->q;
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struct elevator_queue *e = q->elevator;
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struct blk_mq_ctx *ctx = rq->mq_ctx;
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struct blk_mq_hw_ctx *hctx = rq->mq_hctx;
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/* flush rq in flush machinery need to be dispatched directly */
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if (!(rq->rq_flags & RQF_FLUSH_SEQ) && op_is_flush(rq->cmd_flags)) {
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blk_insert_flush(rq);
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goto run;
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}
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WARN_ON(e && (rq->tag != -1));
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if (blk_mq_sched_bypass_insert(hctx, !!e, rq))
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goto run;
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if (e && e->type->ops.insert_requests) {
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LIST_HEAD(list);
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list_add(&rq->queuelist, &list);
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e->type->ops.insert_requests(hctx, &list, at_head);
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} else {
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spin_lock(&ctx->lock);
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__blk_mq_insert_request(hctx, rq, at_head);
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spin_unlock(&ctx->lock);
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}
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run:
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if (run_queue)
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blk_mq_run_hw_queue(hctx, async);
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}
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void blk_mq_sched_insert_requests(struct blk_mq_hw_ctx *hctx,
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struct blk_mq_ctx *ctx,
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struct list_head *list, bool run_queue_async)
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{
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struct elevator_queue *e;
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struct request_queue *q = hctx->queue;
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/*
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* blk_mq_sched_insert_requests() is called from flush plug
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* context only, and hold one usage counter to prevent queue
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* from being released.
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*/
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percpu_ref_get(&q->q_usage_counter);
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e = hctx->queue->elevator;
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if (e && e->type->ops.insert_requests)
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e->type->ops.insert_requests(hctx, list, false);
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else {
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/*
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* try to issue requests directly if the hw queue isn't
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* busy in case of 'none' scheduler, and this way may save
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* us one extra enqueue & dequeue to sw queue.
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*/
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if (!hctx->dispatch_busy && !e && !run_queue_async) {
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blk_mq_try_issue_list_directly(hctx, list);
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if (list_empty(list))
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goto out;
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}
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blk_mq_insert_requests(hctx, ctx, list);
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}
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blk_mq_run_hw_queue(hctx, run_queue_async);
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out:
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percpu_ref_put(&q->q_usage_counter);
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}
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static void blk_mq_sched_free_tags(struct blk_mq_tag_set *set,
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struct blk_mq_hw_ctx *hctx,
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unsigned int hctx_idx)
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{
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if (hctx->sched_tags) {
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blk_mq_free_rqs(set, hctx->sched_tags, hctx_idx);
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blk_mq_free_rq_map(hctx->sched_tags);
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hctx->sched_tags = NULL;
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}
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}
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static int blk_mq_sched_alloc_tags(struct request_queue *q,
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struct blk_mq_hw_ctx *hctx,
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unsigned int hctx_idx)
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{
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struct blk_mq_tag_set *set = q->tag_set;
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int ret;
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hctx->sched_tags = blk_mq_alloc_rq_map(set, hctx_idx, q->nr_requests,
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set->reserved_tags);
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if (!hctx->sched_tags)
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return -ENOMEM;
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ret = blk_mq_alloc_rqs(set, hctx->sched_tags, hctx_idx, q->nr_requests);
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if (ret)
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blk_mq_sched_free_tags(set, hctx, hctx_idx);
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return ret;
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}
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/* called in queue's release handler, tagset has gone away */
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static void blk_mq_sched_tags_teardown(struct request_queue *q)
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{
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struct blk_mq_hw_ctx *hctx;
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int i;
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queue_for_each_hw_ctx(q, hctx, i) {
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if (hctx->sched_tags) {
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blk_mq_free_rq_map(hctx->sched_tags);
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|
hctx->sched_tags = NULL;
|
|
}
|
|
}
|
|
}
|
|
|
|
int blk_mq_init_sched(struct request_queue *q, struct elevator_type *e)
|
|
{
|
|
struct blk_mq_hw_ctx *hctx;
|
|
struct elevator_queue *eq;
|
|
unsigned int i;
|
|
int ret;
|
|
|
|
if (!e) {
|
|
q->elevator = NULL;
|
|
q->nr_requests = q->tag_set->queue_depth;
|
|
return 0;
|
|
}
|
|
|
|
/*
|
|
* Default to double of smaller one between hw queue_depth and 128,
|
|
* since we don't split into sync/async like the old code did.
|
|
* Additionally, this is a per-hw queue depth.
|
|
*/
|
|
q->nr_requests = 2 * min_t(unsigned int, q->tag_set->queue_depth,
|
|
BLKDEV_MAX_RQ);
|
|
|
|
queue_for_each_hw_ctx(q, hctx, i) {
|
|
ret = blk_mq_sched_alloc_tags(q, hctx, i);
|
|
if (ret)
|
|
goto err;
|
|
}
|
|
|
|
ret = e->ops.init_sched(q, e);
|
|
if (ret)
|
|
goto err;
|
|
|
|
blk_mq_debugfs_register_sched(q);
|
|
|
|
queue_for_each_hw_ctx(q, hctx, i) {
|
|
if (e->ops.init_hctx) {
|
|
ret = e->ops.init_hctx(hctx, i);
|
|
if (ret) {
|
|
eq = q->elevator;
|
|
blk_mq_sched_free_requests(q);
|
|
blk_mq_exit_sched(q, eq);
|
|
kobject_put(&eq->kobj);
|
|
return ret;
|
|
}
|
|
}
|
|
blk_mq_debugfs_register_sched_hctx(q, hctx);
|
|
}
|
|
|
|
return 0;
|
|
|
|
err:
|
|
blk_mq_sched_free_requests(q);
|
|
blk_mq_sched_tags_teardown(q);
|
|
q->elevator = NULL;
|
|
return ret;
|
|
}
|
|
|
|
/*
|
|
* called in either blk_queue_cleanup or elevator_switch, tagset
|
|
* is required for freeing requests
|
|
*/
|
|
void blk_mq_sched_free_requests(struct request_queue *q)
|
|
{
|
|
struct blk_mq_hw_ctx *hctx;
|
|
int i;
|
|
|
|
lockdep_assert_held(&q->sysfs_lock);
|
|
|
|
queue_for_each_hw_ctx(q, hctx, i) {
|
|
if (hctx->sched_tags)
|
|
blk_mq_free_rqs(q->tag_set, hctx->sched_tags, i);
|
|
}
|
|
}
|
|
|
|
void blk_mq_exit_sched(struct request_queue *q, struct elevator_queue *e)
|
|
{
|
|
struct blk_mq_hw_ctx *hctx;
|
|
unsigned int i;
|
|
|
|
queue_for_each_hw_ctx(q, hctx, i) {
|
|
blk_mq_debugfs_unregister_sched_hctx(hctx);
|
|
if (e->type->ops.exit_hctx && hctx->sched_data) {
|
|
e->type->ops.exit_hctx(hctx, i);
|
|
hctx->sched_data = NULL;
|
|
}
|
|
}
|
|
blk_mq_debugfs_unregister_sched(q);
|
|
if (e->type->ops.exit_sched)
|
|
e->type->ops.exit_sched(e);
|
|
blk_mq_sched_tags_teardown(q);
|
|
q->elevator = NULL;
|
|
}
|