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![Christoph Hellwig](/assets/img/avatar_default.png)
Various places like I/O schedulers or the QOS infrastructure try to register debugfs files on demans, which can race with creating and removing the main queue debugfs directory. Use the existing debugfs_mutex to serialize all debugfs operations that rely on q->debugfs_dir or the directories hanging off it. To make the teardown code a little simpler declare all debugfs dentry pointers and not just the main one uncoditionally in blkdev.h. Move debugfs_mutex next to the dentries that it protects and document what it is used for. Signed-off-by: Christoph Hellwig <hch@lst.de> Link: https://lore.kernel.org/r/20220614074827.458955-3-hch@lst.de Signed-off-by: Jens Axboe <axboe@kernel.dk>
674 lines
18 KiB
C
674 lines
18 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 <linux/list_sort.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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/*
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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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clear_bit(BLK_MQ_S_SCHED_RESTART, &hctx->state);
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/*
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* Order clearing SCHED_RESTART and list_empty_careful(&hctx->dispatch)
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* in blk_mq_run_hw_queue(). Its pair is the barrier in
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* blk_mq_dispatch_rq_list(). So dispatch code won't see SCHED_RESTART,
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* meantime new request added to hctx->dispatch is missed to check in
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* blk_mq_run_hw_queue().
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*/
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smp_mb();
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blk_mq_run_hw_queue(hctx, true);
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}
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static int sched_rq_cmp(void *priv, const struct list_head *a,
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const struct list_head *b)
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{
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struct request *rqa = container_of(a, struct request, queuelist);
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struct request *rqb = container_of(b, struct request, queuelist);
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return rqa->mq_hctx > rqb->mq_hctx;
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}
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static bool blk_mq_dispatch_hctx_list(struct list_head *rq_list)
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{
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struct blk_mq_hw_ctx *hctx =
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list_first_entry(rq_list, struct request, queuelist)->mq_hctx;
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struct request *rq;
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LIST_HEAD(hctx_list);
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unsigned int count = 0;
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list_for_each_entry(rq, rq_list, queuelist) {
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if (rq->mq_hctx != hctx) {
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list_cut_before(&hctx_list, rq_list, &rq->queuelist);
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goto dispatch;
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}
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count++;
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}
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list_splice_tail_init(rq_list, &hctx_list);
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dispatch:
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return blk_mq_dispatch_rq_list(hctx, &hctx_list, count);
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}
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#define BLK_MQ_BUDGET_DELAY 3 /* ms units */
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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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* Returns -EAGAIN if hctx->dispatch was found non-empty and run_work has to
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* be run again. This is necessary to avoid starving flushes.
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*/
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static int __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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bool multi_hctxs = false, run_queue = false;
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bool dispatched = false, busy = false;
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unsigned int max_dispatch;
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LIST_HEAD(rq_list);
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int count = 0;
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if (hctx->dispatch_busy)
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max_dispatch = 1;
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else
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max_dispatch = hctx->queue->nr_requests;
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do {
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struct request *rq;
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int budget_token;
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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 (!list_empty_careful(&hctx->dispatch)) {
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busy = true;
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break;
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}
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budget_token = blk_mq_get_dispatch_budget(q);
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if (budget_token < 0)
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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(q, budget_token);
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/*
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* We're releasing without dispatching. Holding the
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* budget could have blocked any "hctx"s with the
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* same queue and if we didn't dispatch then there's
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* no guarantee anyone will kick the queue. Kick it
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* ourselves.
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*/
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run_queue = true;
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break;
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}
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blk_mq_set_rq_budget_token(rq, budget_token);
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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_tail(&rq->queuelist, &rq_list);
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count++;
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if (rq->mq_hctx != hctx)
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multi_hctxs = true;
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/*
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* If we cannot get tag for the request, stop dequeueing
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* requests from the IO scheduler. We are unlikely to be able
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* to submit them anyway and it creates false impression for
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* scheduling heuristics that the device can take more IO.
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*/
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if (!blk_mq_get_driver_tag(rq))
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break;
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} while (count < max_dispatch);
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if (!count) {
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if (run_queue)
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blk_mq_delay_run_hw_queues(q, BLK_MQ_BUDGET_DELAY);
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} else if (multi_hctxs) {
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/*
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* Requests from different hctx may be dequeued from some
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* schedulers, such as bfq and deadline.
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*
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* Sort the requests in the list according to their hctx,
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* dispatch batching requests from same hctx at a time.
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*/
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list_sort(NULL, &rq_list, sched_rq_cmp);
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do {
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dispatched |= blk_mq_dispatch_hctx_list(&rq_list);
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} while (!list_empty(&rq_list));
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} else {
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dispatched = blk_mq_dispatch_rq_list(hctx, &rq_list, count);
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}
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if (busy)
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return -EAGAIN;
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return !!dispatched;
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}
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static int blk_mq_do_dispatch_sched(struct blk_mq_hw_ctx *hctx)
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{
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unsigned long end = jiffies + HZ;
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int ret;
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do {
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ret = __blk_mq_do_dispatch_sched(hctx);
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if (ret != 1)
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break;
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if (need_resched() || time_is_before_jiffies(end)) {
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blk_mq_delay_run_hw_queue(hctx, 0);
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break;
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}
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} while (1);
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return ret;
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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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* Returns -EAGAIN if hctx->dispatch was found non-empty and run_work has to
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* be run again. This is necessary to avoid starving flushes.
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*/
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static int 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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int ret = 0;
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struct request *rq;
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do {
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int budget_token;
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if (!list_empty_careful(&hctx->dispatch)) {
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ret = -EAGAIN;
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break;
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}
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if (!sbitmap_any_bit_set(&hctx->ctx_map))
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break;
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budget_token = blk_mq_get_dispatch_budget(q);
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if (budget_token < 0)
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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(q, budget_token);
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/*
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* We're releasing without dispatching. Holding the
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* budget could have blocked any "hctx"s with the
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* same queue and if we didn't dispatch then there's
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* no guarantee anyone will kick the queue. Kick it
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* ourselves.
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*/
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blk_mq_delay_run_hw_queues(q, BLK_MQ_BUDGET_DELAY);
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break;
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}
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blk_mq_set_rq_budget_token(rq, budget_token);
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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(rq->mq_hctx, &rq_list, 1));
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WRITE_ONCE(hctx->dispatch_from, ctx);
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return ret;
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}
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static int __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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const bool has_sched = q->elevator;
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int ret = 0;
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LIST_HEAD(rq_list);
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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(hctx, &rq_list, 0)) {
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if (has_sched)
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ret = blk_mq_do_dispatch_sched(hctx);
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else
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ret = blk_mq_do_dispatch_ctx(hctx);
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}
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} else if (has_sched) {
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ret = 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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ret = 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(hctx, &rq_list, 0);
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}
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return ret;
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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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/* 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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* A return of -EAGAIN is an indication that hctx->dispatch is not
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* empty and we must run again in order to avoid starving flushes.
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*/
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if (__blk_mq_sched_dispatch_requests(hctx) == -EAGAIN) {
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if (__blk_mq_sched_dispatch_requests(hctx) == -EAGAIN)
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blk_mq_run_hw_queue(hctx, true);
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}
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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;
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struct blk_mq_hw_ctx *hctx;
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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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ret = e->type->ops.bio_merge(q, bio, nr_segs);
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goto out_put;
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}
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ctx = blk_mq_get_ctx(q);
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hctx = blk_mq_map_queue(q, bio->bi_opf, ctx);
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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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goto out_put;
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/* default per sw-queue merge */
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spin_lock(&ctx->lock);
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/*
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* Reverse check our software queue for entries that we could
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* potentially merge with. Currently includes a hand-wavy stop
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* count of 8, to not spend too much time checking for merges.
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*/
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if (blk_bio_list_merge(q, &ctx->rq_lists[type], bio, nr_segs))
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ret = true;
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spin_unlock(&ctx->lock);
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out_put:
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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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struct list_head *free)
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{
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return rq_mergeable(rq) && elv_attempt_insert_merge(q, rq, free);
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}
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EXPORT_SYMBOL_GPL(blk_mq_sched_try_insert_merge);
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static bool blk_mq_sched_bypass_insert(struct blk_mq_hw_ctx *hctx,
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struct request *rq)
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{
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/*
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* dispatch flush and passthrough rq directly
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*
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* passthrough request has to be added to hctx->dispatch directly.
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* For some reason, device may be in one situation which can't
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* handle FS request, so STS_RESOURCE is always returned and the
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* FS request will be added to hctx->dispatch. However passthrough
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* request may be required at that time for fixing the problem. If
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* passthrough request is added to scheduler queue, there isn't any
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* chance to dispatch it given we prioritize requests in hctx->dispatch.
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*/
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if ((rq->rq_flags & RQF_FLUSH_SEQ) || blk_rq_is_passthrough(rq))
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return true;
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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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WARN_ON(e && (rq->tag != BLK_MQ_NO_TAG));
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if (blk_mq_sched_bypass_insert(hctx, rq)) {
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/*
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* Firstly normal IO request is inserted to scheduler queue or
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* sw queue, meantime we add flush request to dispatch queue(
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* hctx->dispatch) directly and there is at most one in-flight
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* flush request for each hw queue, so it doesn't matter to add
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* flush request to tail or front of the dispatch queue.
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*
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* Secondly in case of NCQ, flush request belongs to non-NCQ
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* command, and queueing it will fail when there is any
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* in-flight normal IO request(NCQ command). When adding flush
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* rq to the front of hctx->dispatch, it is easier to introduce
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* extra time to flush rq's latency because of S_SCHED_RESTART
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* compared with adding to the tail of dispatch queue, then
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* chance of flush merge is increased, and less flush requests
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* will be issued to controller. It is observed that ~10% time
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* is saved in blktests block/004 on disk attached to AHCI/NCQ
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* drive when adding flush rq to the front of hctx->dispatch.
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*
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* Simply queue flush rq to the front of hctx->dispatch so that
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* intensive flush workloads can benefit in case of NCQ HW.
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*/
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at_head = (rq->rq_flags & RQF_FLUSH_SEQ) ? true : at_head;
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blk_mq_request_bypass_insert(rq, at_head, false);
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goto run;
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}
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if (e) {
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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) {
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e->type->ops.insert_requests(hctx, list, false);
|
|
} else {
|
|
/*
|
|
* try to issue requests directly if the hw queue isn't
|
|
* busy in case of 'none' scheduler, and this way may save
|
|
* us one extra enqueue & dequeue to sw queue.
|
|
*/
|
|
if (!hctx->dispatch_busy && !run_queue_async) {
|
|
blk_mq_run_dispatch_ops(hctx->queue,
|
|
blk_mq_try_issue_list_directly(hctx, list));
|
|
if (list_empty(list))
|
|
goto out;
|
|
}
|
|
blk_mq_insert_requests(hctx, ctx, list);
|
|
}
|
|
|
|
blk_mq_run_hw_queue(hctx, run_queue_async);
|
|
out:
|
|
percpu_ref_put(&q->q_usage_counter);
|
|
}
|
|
|
|
static int blk_mq_sched_alloc_map_and_rqs(struct request_queue *q,
|
|
struct blk_mq_hw_ctx *hctx,
|
|
unsigned int hctx_idx)
|
|
{
|
|
if (blk_mq_is_shared_tags(q->tag_set->flags)) {
|
|
hctx->sched_tags = q->sched_shared_tags;
|
|
return 0;
|
|
}
|
|
|
|
hctx->sched_tags = blk_mq_alloc_map_and_rqs(q->tag_set, hctx_idx,
|
|
q->nr_requests);
|
|
|
|
if (!hctx->sched_tags)
|
|
return -ENOMEM;
|
|
return 0;
|
|
}
|
|
|
|
static void blk_mq_exit_sched_shared_tags(struct request_queue *queue)
|
|
{
|
|
blk_mq_free_rq_map(queue->sched_shared_tags);
|
|
queue->sched_shared_tags = NULL;
|
|
}
|
|
|
|
/* called in queue's release handler, tagset has gone away */
|
|
static void blk_mq_sched_tags_teardown(struct request_queue *q, unsigned int flags)
|
|
{
|
|
struct blk_mq_hw_ctx *hctx;
|
|
unsigned long i;
|
|
|
|
queue_for_each_hw_ctx(q, hctx, i) {
|
|
if (hctx->sched_tags) {
|
|
if (!blk_mq_is_shared_tags(flags))
|
|
blk_mq_free_rq_map(hctx->sched_tags);
|
|
hctx->sched_tags = NULL;
|
|
}
|
|
}
|
|
|
|
if (blk_mq_is_shared_tags(flags))
|
|
blk_mq_exit_sched_shared_tags(q);
|
|
}
|
|
|
|
static int blk_mq_init_sched_shared_tags(struct request_queue *queue)
|
|
{
|
|
struct blk_mq_tag_set *set = queue->tag_set;
|
|
|
|
/*
|
|
* Set initial depth at max so that we don't need to reallocate for
|
|
* updating nr_requests.
|
|
*/
|
|
queue->sched_shared_tags = blk_mq_alloc_map_and_rqs(set,
|
|
BLK_MQ_NO_HCTX_IDX,
|
|
MAX_SCHED_RQ);
|
|
if (!queue->sched_shared_tags)
|
|
return -ENOMEM;
|
|
|
|
blk_mq_tag_update_sched_shared_tags(queue);
|
|
|
|
return 0;
|
|
}
|
|
|
|
int blk_mq_init_sched(struct request_queue *q, struct elevator_type *e)
|
|
{
|
|
unsigned int flags = q->tag_set->flags;
|
|
struct blk_mq_hw_ctx *hctx;
|
|
struct elevator_queue *eq;
|
|
unsigned long i;
|
|
int ret;
|
|
|
|
if (!e) {
|
|
blk_queue_flag_clear(QUEUE_FLAG_SQ_SCHED, q);
|
|
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_DEFAULT_RQ);
|
|
|
|
if (blk_mq_is_shared_tags(flags)) {
|
|
ret = blk_mq_init_sched_shared_tags(q);
|
|
if (ret)
|
|
return ret;
|
|
}
|
|
|
|
queue_for_each_hw_ctx(q, hctx, i) {
|
|
ret = blk_mq_sched_alloc_map_and_rqs(q, hctx, i);
|
|
if (ret)
|
|
goto err_free_map_and_rqs;
|
|
}
|
|
|
|
ret = e->ops.init_sched(q, e);
|
|
if (ret)
|
|
goto err_free_map_and_rqs;
|
|
|
|
mutex_lock(&q->debugfs_mutex);
|
|
blk_mq_debugfs_register_sched(q);
|
|
mutex_unlock(&q->debugfs_mutex);
|
|
|
|
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_rqs(q);
|
|
blk_mq_exit_sched(q, eq);
|
|
kobject_put(&eq->kobj);
|
|
return ret;
|
|
}
|
|
}
|
|
mutex_lock(&q->debugfs_mutex);
|
|
blk_mq_debugfs_register_sched_hctx(q, hctx);
|
|
mutex_unlock(&q->debugfs_mutex);
|
|
}
|
|
|
|
return 0;
|
|
|
|
err_free_map_and_rqs:
|
|
blk_mq_sched_free_rqs(q);
|
|
blk_mq_sched_tags_teardown(q, flags);
|
|
|
|
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_rqs(struct request_queue *q)
|
|
{
|
|
struct blk_mq_hw_ctx *hctx;
|
|
unsigned long i;
|
|
|
|
if (blk_mq_is_shared_tags(q->tag_set->flags)) {
|
|
blk_mq_free_rqs(q->tag_set, q->sched_shared_tags,
|
|
BLK_MQ_NO_HCTX_IDX);
|
|
} else {
|
|
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 long i;
|
|
unsigned int flags = 0;
|
|
|
|
queue_for_each_hw_ctx(q, hctx, i) {
|
|
mutex_lock(&q->debugfs_mutex);
|
|
blk_mq_debugfs_unregister_sched_hctx(hctx);
|
|
mutex_unlock(&q->debugfs_mutex);
|
|
|
|
if (e->type->ops.exit_hctx && hctx->sched_data) {
|
|
e->type->ops.exit_hctx(hctx, i);
|
|
hctx->sched_data = NULL;
|
|
}
|
|
flags = hctx->flags;
|
|
}
|
|
|
|
mutex_lock(&q->debugfs_mutex);
|
|
blk_mq_debugfs_unregister_sched(q);
|
|
mutex_unlock(&q->debugfs_mutex);
|
|
|
|
if (e->type->ops.exit_sched)
|
|
e->type->ops.exit_sched(e);
|
|
blk_mq_sched_tags_teardown(q, flags);
|
|
q->elevator = NULL;
|
|
}
|