linux/block/blk-mq-sched.c
Jens Axboe 79f720a751 blk-mq: only run the hardware queue if IO is pending
Currently we are inconsistent in when we decide to run the queue. Using
blk_mq_run_hw_queues() we check if the hctx has pending IO before
running it, but we don't do that from the individual queue run function,
blk_mq_run_hw_queue(). This results in a lot of extra and pointless
queue runs, potentially, on flush requests and (much worse) on tag
starvation situations. This is observable just looking at top output,
with lots of kworkers active. For the !async runs, it just adds to the
CPU overhead of blk-mq.

Move the has-pending check into the run function instead of having
callers do it.

Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
2017-11-10 19:55:57 -07:00

646 lines
16 KiB
C

/*
* blk-mq scheduling framework
*
* Copyright (C) 2016 Jens Axboe
*/
#include <linux/kernel.h>
#include <linux/module.h>
#include <linux/blk-mq.h>
#include <trace/events/block.h>
#include "blk.h"
#include "blk-mq.h"
#include "blk-mq-debugfs.h"
#include "blk-mq-sched.h"
#include "blk-mq-tag.h"
#include "blk-wbt.h"
void blk_mq_sched_free_hctx_data(struct request_queue *q,
void (*exit)(struct blk_mq_hw_ctx *))
{
struct blk_mq_hw_ctx *hctx;
int i;
queue_for_each_hw_ctx(q, hctx, i) {
if (exit && hctx->sched_data)
exit(hctx);
kfree(hctx->sched_data);
hctx->sched_data = NULL;
}
}
EXPORT_SYMBOL_GPL(blk_mq_sched_free_hctx_data);
void blk_mq_sched_assign_ioc(struct request *rq, struct bio *bio)
{
struct request_queue *q = rq->q;
struct io_context *ioc = rq_ioc(bio);
struct io_cq *icq;
spin_lock_irq(q->queue_lock);
icq = ioc_lookup_icq(ioc, q);
spin_unlock_irq(q->queue_lock);
if (!icq) {
icq = ioc_create_icq(ioc, q, GFP_ATOMIC);
if (!icq)
return;
}
get_io_context(icq->ioc);
rq->elv.icq = icq;
}
/*
* Mark a hardware queue as needing a restart. For shared queues, maintain
* a count of how many hardware queues are marked for restart.
*/
static void blk_mq_sched_mark_restart_hctx(struct blk_mq_hw_ctx *hctx)
{
if (test_bit(BLK_MQ_S_SCHED_RESTART, &hctx->state))
return;
if (hctx->flags & BLK_MQ_F_TAG_SHARED) {
struct request_queue *q = hctx->queue;
if (!test_and_set_bit(BLK_MQ_S_SCHED_RESTART, &hctx->state))
atomic_inc(&q->shared_hctx_restart);
} else
set_bit(BLK_MQ_S_SCHED_RESTART, &hctx->state);
}
static bool blk_mq_sched_restart_hctx(struct blk_mq_hw_ctx *hctx)
{
if (!test_bit(BLK_MQ_S_SCHED_RESTART, &hctx->state))
return false;
if (hctx->flags & BLK_MQ_F_TAG_SHARED) {
struct request_queue *q = hctx->queue;
if (test_and_clear_bit(BLK_MQ_S_SCHED_RESTART, &hctx->state))
atomic_dec(&q->shared_hctx_restart);
} else
clear_bit(BLK_MQ_S_SCHED_RESTART, &hctx->state);
return blk_mq_run_hw_queue(hctx, true);
}
/*
* Only SCSI implements .get_budget and .put_budget, and SCSI restarts
* its queue by itself in its completion handler, so we don't need to
* restart queue if .get_budget() returns BLK_STS_NO_RESOURCE.
*/
static void blk_mq_do_dispatch_sched(struct blk_mq_hw_ctx *hctx)
{
struct request_queue *q = hctx->queue;
struct elevator_queue *e = q->elevator;
LIST_HEAD(rq_list);
do {
struct request *rq;
if (e->type->ops.mq.has_work &&
!e->type->ops.mq.has_work(hctx))
break;
if (!blk_mq_get_dispatch_budget(hctx))
break;
rq = e->type->ops.mq.dispatch_request(hctx);
if (!rq) {
blk_mq_put_dispatch_budget(hctx);
break;
}
/*
* Now this rq owns the budget which has to be released
* if this rq won't be queued to driver via .queue_rq()
* in blk_mq_dispatch_rq_list().
*/
list_add(&rq->queuelist, &rq_list);
} while (blk_mq_dispatch_rq_list(q, &rq_list, true));
}
static struct blk_mq_ctx *blk_mq_next_ctx(struct blk_mq_hw_ctx *hctx,
struct blk_mq_ctx *ctx)
{
unsigned idx = ctx->index_hw;
if (++idx == hctx->nr_ctx)
idx = 0;
return hctx->ctxs[idx];
}
/*
* Only SCSI implements .get_budget and .put_budget, and SCSI restarts
* its queue by itself in its completion handler, so we don't need to
* restart queue if .get_budget() returns BLK_STS_NO_RESOURCE.
*/
static void blk_mq_do_dispatch_ctx(struct blk_mq_hw_ctx *hctx)
{
struct request_queue *q = hctx->queue;
LIST_HEAD(rq_list);
struct blk_mq_ctx *ctx = READ_ONCE(hctx->dispatch_from);
do {
struct request *rq;
if (!sbitmap_any_bit_set(&hctx->ctx_map))
break;
if (!blk_mq_get_dispatch_budget(hctx))
break;
rq = blk_mq_dequeue_from_ctx(hctx, ctx);
if (!rq) {
blk_mq_put_dispatch_budget(hctx);
break;
}
/*
* Now this rq owns the budget which has to be released
* if this rq won't be queued to driver via .queue_rq()
* in blk_mq_dispatch_rq_list().
*/
list_add(&rq->queuelist, &rq_list);
/* round robin for fair dispatch */
ctx = blk_mq_next_ctx(hctx, rq->mq_ctx);
} while (blk_mq_dispatch_rq_list(q, &rq_list, true));
WRITE_ONCE(hctx->dispatch_from, ctx);
}
/* return true if hw queue need to be run again */
void blk_mq_sched_dispatch_requests(struct blk_mq_hw_ctx *hctx)
{
struct request_queue *q = hctx->queue;
struct elevator_queue *e = q->elevator;
const bool has_sched_dispatch = e && e->type->ops.mq.dispatch_request;
LIST_HEAD(rq_list);
/* RCU or SRCU read lock is needed before checking quiesced flag */
if (unlikely(blk_mq_hctx_stopped(hctx) || blk_queue_quiesced(q)))
return;
hctx->run++;
/*
* If we have previous entries on our dispatch list, grab them first for
* more fair dispatch.
*/
if (!list_empty_careful(&hctx->dispatch)) {
spin_lock(&hctx->lock);
if (!list_empty(&hctx->dispatch))
list_splice_init(&hctx->dispatch, &rq_list);
spin_unlock(&hctx->lock);
}
/*
* Only ask the scheduler for requests, if we didn't have residual
* requests from the dispatch list. This is to avoid the case where
* we only ever dispatch a fraction of the requests available because
* of low device queue depth. Once we pull requests out of the IO
* scheduler, we can no longer merge or sort them. So it's best to
* leave them there for as long as we can. Mark the hw queue as
* needing a restart in that case.
*
* We want to dispatch from the scheduler if there was nothing
* on the dispatch list or we were able to dispatch from the
* dispatch list.
*/
if (!list_empty(&rq_list)) {
blk_mq_sched_mark_restart_hctx(hctx);
if (blk_mq_dispatch_rq_list(q, &rq_list, false)) {
if (has_sched_dispatch)
blk_mq_do_dispatch_sched(hctx);
else
blk_mq_do_dispatch_ctx(hctx);
}
} else if (has_sched_dispatch) {
blk_mq_do_dispatch_sched(hctx);
} else if (q->mq_ops->get_budget) {
/*
* If we need to get budget before queuing request, we
* dequeue request one by one from sw queue for avoiding
* to mess up I/O merge when dispatch runs out of resource.
*
* TODO: get more budgets, and dequeue more requests in
* one time.
*/
blk_mq_do_dispatch_ctx(hctx);
} else {
blk_mq_flush_busy_ctxs(hctx, &rq_list);
blk_mq_dispatch_rq_list(q, &rq_list, false);
}
}
bool blk_mq_sched_try_merge(struct request_queue *q, struct bio *bio,
struct request **merged_request)
{
struct request *rq;
switch (elv_merge(q, &rq, bio)) {
case ELEVATOR_BACK_MERGE:
if (!blk_mq_sched_allow_merge(q, rq, bio))
return false;
if (!bio_attempt_back_merge(q, rq, bio))
return false;
*merged_request = attempt_back_merge(q, rq);
if (!*merged_request)
elv_merged_request(q, rq, ELEVATOR_BACK_MERGE);
return true;
case ELEVATOR_FRONT_MERGE:
if (!blk_mq_sched_allow_merge(q, rq, bio))
return false;
if (!bio_attempt_front_merge(q, rq, bio))
return false;
*merged_request = attempt_front_merge(q, rq);
if (!*merged_request)
elv_merged_request(q, rq, ELEVATOR_FRONT_MERGE);
return true;
default:
return false;
}
}
EXPORT_SYMBOL_GPL(blk_mq_sched_try_merge);
/*
* Reverse check our software queue for entries that we could potentially
* merge with. Currently includes a hand-wavy stop count of 8, to not spend
* too much time checking for merges.
*/
static bool blk_mq_attempt_merge(struct request_queue *q,
struct blk_mq_ctx *ctx, struct bio *bio)
{
struct request *rq;
int checked = 8;
lockdep_assert_held(&ctx->lock);
list_for_each_entry_reverse(rq, &ctx->rq_list, queuelist) {
bool merged = false;
if (!checked--)
break;
if (!blk_rq_merge_ok(rq, bio))
continue;
switch (blk_try_merge(rq, bio)) {
case ELEVATOR_BACK_MERGE:
if (blk_mq_sched_allow_merge(q, rq, bio))
merged = bio_attempt_back_merge(q, rq, bio);
break;
case ELEVATOR_FRONT_MERGE:
if (blk_mq_sched_allow_merge(q, rq, bio))
merged = bio_attempt_front_merge(q, rq, bio);
break;
case ELEVATOR_DISCARD_MERGE:
merged = bio_attempt_discard_merge(q, rq, bio);
break;
default:
continue;
}
if (merged)
ctx->rq_merged++;
return merged;
}
return false;
}
bool __blk_mq_sched_bio_merge(struct request_queue *q, struct bio *bio)
{
struct elevator_queue *e = q->elevator;
struct blk_mq_ctx *ctx = blk_mq_get_ctx(q);
struct blk_mq_hw_ctx *hctx = blk_mq_map_queue(q, ctx->cpu);
bool ret = false;
if (e && e->type->ops.mq.bio_merge) {
blk_mq_put_ctx(ctx);
return e->type->ops.mq.bio_merge(hctx, bio);
}
if (hctx->flags & BLK_MQ_F_SHOULD_MERGE) {
/* default per sw-queue merge */
spin_lock(&ctx->lock);
ret = blk_mq_attempt_merge(q, ctx, bio);
spin_unlock(&ctx->lock);
}
blk_mq_put_ctx(ctx);
return ret;
}
bool blk_mq_sched_try_insert_merge(struct request_queue *q, struct request *rq)
{
return rq_mergeable(rq) && elv_attempt_insert_merge(q, rq);
}
EXPORT_SYMBOL_GPL(blk_mq_sched_try_insert_merge);
void blk_mq_sched_request_inserted(struct request *rq)
{
trace_block_rq_insert(rq->q, rq);
}
EXPORT_SYMBOL_GPL(blk_mq_sched_request_inserted);
static bool blk_mq_sched_bypass_insert(struct blk_mq_hw_ctx *hctx,
bool has_sched,
struct request *rq)
{
/* dispatch flush rq directly */
if (rq->rq_flags & RQF_FLUSH_SEQ) {
spin_lock(&hctx->lock);
list_add(&rq->queuelist, &hctx->dispatch);
spin_unlock(&hctx->lock);
return true;
}
if (has_sched)
rq->rq_flags |= RQF_SORTED;
return false;
}
/**
* list_for_each_entry_rcu_rr - iterate in a round-robin fashion over rcu list
* @pos: loop cursor.
* @skip: the list element that will not be examined. Iteration starts at
* @skip->next.
* @head: head of the list to examine. This list must have at least one
* element, namely @skip.
* @member: name of the list_head structure within typeof(*pos).
*/
#define list_for_each_entry_rcu_rr(pos, skip, head, member) \
for ((pos) = (skip); \
(pos = (pos)->member.next != (head) ? list_entry_rcu( \
(pos)->member.next, typeof(*pos), member) : \
list_entry_rcu((pos)->member.next->next, typeof(*pos), member)), \
(pos) != (skip); )
/*
* Called after a driver tag has been freed to check whether a hctx needs to
* be restarted. Restarts @hctx if its tag set is not shared. Restarts hardware
* queues in a round-robin fashion if the tag set of @hctx is shared with other
* hardware queues.
*/
void blk_mq_sched_restart(struct blk_mq_hw_ctx *const hctx)
{
struct blk_mq_tags *const tags = hctx->tags;
struct blk_mq_tag_set *const set = hctx->queue->tag_set;
struct request_queue *const queue = hctx->queue, *q;
struct blk_mq_hw_ctx *hctx2;
unsigned int i, j;
if (set->flags & BLK_MQ_F_TAG_SHARED) {
/*
* If this is 0, then we know that no hardware queues
* have RESTART marked. We're done.
*/
if (!atomic_read(&queue->shared_hctx_restart))
return;
rcu_read_lock();
list_for_each_entry_rcu_rr(q, queue, &set->tag_list,
tag_set_list) {
queue_for_each_hw_ctx(q, hctx2, i)
if (hctx2->tags == tags &&
blk_mq_sched_restart_hctx(hctx2))
goto done;
}
j = hctx->queue_num + 1;
for (i = 0; i < queue->nr_hw_queues; i++, j++) {
if (j == queue->nr_hw_queues)
j = 0;
hctx2 = queue->queue_hw_ctx[j];
if (hctx2->tags == tags &&
blk_mq_sched_restart_hctx(hctx2))
break;
}
done:
rcu_read_unlock();
} else {
blk_mq_sched_restart_hctx(hctx);
}
}
void blk_mq_sched_insert_request(struct request *rq, bool at_head,
bool run_queue, bool async, bool can_block)
{
struct request_queue *q = rq->q;
struct elevator_queue *e = q->elevator;
struct blk_mq_ctx *ctx = rq->mq_ctx;
struct blk_mq_hw_ctx *hctx = blk_mq_map_queue(q, ctx->cpu);
/* flush rq in flush machinery need to be dispatched directly */
if (!(rq->rq_flags & RQF_FLUSH_SEQ) && op_is_flush(rq->cmd_flags)) {
blk_insert_flush(rq);
goto run;
}
WARN_ON(e && (rq->tag != -1));
if (blk_mq_sched_bypass_insert(hctx, !!e, rq))
goto run;
if (e && e->type->ops.mq.insert_requests) {
LIST_HEAD(list);
list_add(&rq->queuelist, &list);
e->type->ops.mq.insert_requests(hctx, &list, at_head);
} else {
spin_lock(&ctx->lock);
__blk_mq_insert_request(hctx, rq, at_head);
spin_unlock(&ctx->lock);
}
run:
if (run_queue)
blk_mq_run_hw_queue(hctx, async);
}
void blk_mq_sched_insert_requests(struct request_queue *q,
struct blk_mq_ctx *ctx,
struct list_head *list, bool run_queue_async)
{
struct blk_mq_hw_ctx *hctx = blk_mq_map_queue(q, ctx->cpu);
struct elevator_queue *e = hctx->queue->elevator;
if (e && e->type->ops.mq.insert_requests)
e->type->ops.mq.insert_requests(hctx, list, false);
else
blk_mq_insert_requests(hctx, ctx, list);
blk_mq_run_hw_queue(hctx, run_queue_async);
}
static void blk_mq_sched_free_tags(struct blk_mq_tag_set *set,
struct blk_mq_hw_ctx *hctx,
unsigned int hctx_idx)
{
if (hctx->sched_tags) {
blk_mq_free_rqs(set, hctx->sched_tags, hctx_idx);
blk_mq_free_rq_map(hctx->sched_tags);
hctx->sched_tags = NULL;
}
}
static int blk_mq_sched_alloc_tags(struct request_queue *q,
struct blk_mq_hw_ctx *hctx,
unsigned int hctx_idx)
{
struct blk_mq_tag_set *set = q->tag_set;
int ret;
hctx->sched_tags = blk_mq_alloc_rq_map(set, hctx_idx, q->nr_requests,
set->reserved_tags);
if (!hctx->sched_tags)
return -ENOMEM;
ret = blk_mq_alloc_rqs(set, hctx->sched_tags, hctx_idx, q->nr_requests);
if (ret)
blk_mq_sched_free_tags(set, hctx, hctx_idx);
return ret;
}
static void blk_mq_sched_tags_teardown(struct request_queue *q)
{
struct blk_mq_tag_set *set = q->tag_set;
struct blk_mq_hw_ctx *hctx;
int i;
queue_for_each_hw_ctx(q, hctx, i)
blk_mq_sched_free_tags(set, hctx, i);
}
int blk_mq_sched_init_hctx(struct request_queue *q, struct blk_mq_hw_ctx *hctx,
unsigned int hctx_idx)
{
struct elevator_queue *e = q->elevator;
int ret;
if (!e)
return 0;
ret = blk_mq_sched_alloc_tags(q, hctx, hctx_idx);
if (ret)
return ret;
if (e->type->ops.mq.init_hctx) {
ret = e->type->ops.mq.init_hctx(hctx, hctx_idx);
if (ret) {
blk_mq_sched_free_tags(q->tag_set, hctx, hctx_idx);
return ret;
}
}
blk_mq_debugfs_register_sched_hctx(q, hctx);
return 0;
}
void blk_mq_sched_exit_hctx(struct request_queue *q, struct blk_mq_hw_ctx *hctx,
unsigned int hctx_idx)
{
struct elevator_queue *e = q->elevator;
if (!e)
return;
blk_mq_debugfs_unregister_sched_hctx(hctx);
if (e->type->ops.mq.exit_hctx && hctx->sched_data) {
e->type->ops.mq.exit_hctx(hctx, hctx_idx);
hctx->sched_data = NULL;
}
blk_mq_sched_free_tags(q->tag_set, hctx, hctx_idx);
}
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;
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.mq.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.mq.init_hctx) {
ret = e->ops.mq.init_hctx(hctx, i);
if (ret) {
eq = q->elevator;
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_tags_teardown(q);
q->elevator = NULL;
return ret;
}
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.mq.exit_hctx && hctx->sched_data) {
e->type->ops.mq.exit_hctx(hctx, i);
hctx->sched_data = NULL;
}
}
blk_mq_debugfs_unregister_sched(q);
if (e->type->ops.mq.exit_sched)
e->type->ops.mq.exit_sched(e);
blk_mq_sched_tags_teardown(q);
q->elevator = NULL;
}
int blk_mq_sched_init(struct request_queue *q)
{
int ret;
mutex_lock(&q->sysfs_lock);
ret = elevator_init(q, NULL);
mutex_unlock(&q->sysfs_lock);
return ret;
}