linux/block/blk-mq-sched.c
Ming Lei 2a5a24aa83 scsi: blk-mq: Return budget token from .get_budget callback
SCSI uses a global atomic variable to track queue depth for each
LUN/request queue.

This doesn't scale well when there are lots of CPU cores and the disk is
very fast. It has been observed that IOPS is affected a lot by tracking
queue depth via sdev->device_busy in the I/O path.

Return budget token from .get_budget callback. The budget token can be
passed to driver so that we can replace the atomic variable with
sbitmap_queue and alleviate the scaling problems that way.

Link: https://lore.kernel.org/r/20210122023317.687987-9-ming.lei@redhat.com
Cc: Omar Sandoval <osandov@fb.com>
Cc: Kashyap Desai <kashyap.desai@broadcom.com>
Cc: Sumanesh Samanta <sumanesh.samanta@broadcom.com>
Cc: Ewan D. Milne <emilne@redhat.com>
Tested-by: Sumanesh Samanta <sumanesh.samanta@broadcom.com>
Reviewed-by: Hannes Reinecke <hare@suse.de>
Signed-off-by: Ming Lei <ming.lei@redhat.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>
2021-03-04 17:36:59 -05:00

649 lines
17 KiB
C

// SPDX-License-Identifier: GPL-2.0
/*
* blk-mq scheduling framework
*
* Copyright (C) 2016 Jens Axboe
*/
#include <linux/kernel.h>
#include <linux/module.h>
#include <linux/blk-mq.h>
#include <linux/list_sort.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_assign_ioc(struct request *rq)
{
struct request_queue *q = rq->q;
struct io_context *ioc;
struct io_cq *icq;
/*
* May not have an IO context if it's a passthrough request
*/
ioc = current->io_context;
if (!ioc)
return;
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.
*/
void blk_mq_sched_mark_restart_hctx(struct blk_mq_hw_ctx *hctx)
{
if (test_bit(BLK_MQ_S_SCHED_RESTART, &hctx->state))
return;
set_bit(BLK_MQ_S_SCHED_RESTART, &hctx->state);
}
EXPORT_SYMBOL_GPL(blk_mq_sched_mark_restart_hctx);
void blk_mq_sched_restart(struct blk_mq_hw_ctx *hctx)
{
if (!test_bit(BLK_MQ_S_SCHED_RESTART, &hctx->state))
return;
clear_bit(BLK_MQ_S_SCHED_RESTART, &hctx->state);
/*
* Order clearing SCHED_RESTART and list_empty_careful(&hctx->dispatch)
* in blk_mq_run_hw_queue(). Its pair is the barrier in
* blk_mq_dispatch_rq_list(). So dispatch code won't see SCHED_RESTART,
* meantime new request added to hctx->dispatch is missed to check in
* blk_mq_run_hw_queue().
*/
smp_mb();
blk_mq_run_hw_queue(hctx, true);
}
static int sched_rq_cmp(void *priv, struct list_head *a, struct list_head *b)
{
struct request *rqa = container_of(a, struct request, queuelist);
struct request *rqb = container_of(b, struct request, queuelist);
return rqa->mq_hctx > rqb->mq_hctx;
}
static bool blk_mq_dispatch_hctx_list(struct list_head *rq_list)
{
struct blk_mq_hw_ctx *hctx =
list_first_entry(rq_list, struct request, queuelist)->mq_hctx;
struct request *rq;
LIST_HEAD(hctx_list);
unsigned int count = 0;
list_for_each_entry(rq, rq_list, queuelist) {
if (rq->mq_hctx != hctx) {
list_cut_before(&hctx_list, rq_list, &rq->queuelist);
goto dispatch;
}
count++;
}
list_splice_tail_init(rq_list, &hctx_list);
dispatch:
return blk_mq_dispatch_rq_list(hctx, &hctx_list, count);
}
#define BLK_MQ_BUDGET_DELAY 3 /* ms units */
/*
* 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.
*
* Returns -EAGAIN if hctx->dispatch was found non-empty and run_work has to
* be run again. This is necessary to avoid starving flushes.
*/
static int __blk_mq_do_dispatch_sched(struct blk_mq_hw_ctx *hctx)
{
struct request_queue *q = hctx->queue;
struct elevator_queue *e = q->elevator;
bool multi_hctxs = false, run_queue = false;
bool dispatched = false, busy = false;
unsigned int max_dispatch;
LIST_HEAD(rq_list);
int count = 0;
if (hctx->dispatch_busy)
max_dispatch = 1;
else
max_dispatch = hctx->queue->nr_requests;
do {
struct request *rq;
int budget_token;
if (e->type->ops.has_work && !e->type->ops.has_work(hctx))
break;
if (!list_empty_careful(&hctx->dispatch)) {
busy = true;
break;
}
budget_token = blk_mq_get_dispatch_budget(q);
if (budget_token < 0)
break;
rq = e->type->ops.dispatch_request(hctx);
if (!rq) {
blk_mq_put_dispatch_budget(q, budget_token);
/*
* We're releasing without dispatching. Holding the
* budget could have blocked any "hctx"s with the
* same queue and if we didn't dispatch then there's
* no guarantee anyone will kick the queue. Kick it
* ourselves.
*/
run_queue = true;
break;
}
blk_mq_set_rq_budget_token(rq, budget_token);
/*
* 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_tail(&rq->queuelist, &rq_list);
if (rq->mq_hctx != hctx)
multi_hctxs = true;
} while (++count < max_dispatch);
if (!count) {
if (run_queue)
blk_mq_delay_run_hw_queues(q, BLK_MQ_BUDGET_DELAY);
} else if (multi_hctxs) {
/*
* Requests from different hctx may be dequeued from some
* schedulers, such as bfq and deadline.
*
* Sort the requests in the list according to their hctx,
* dispatch batching requests from same hctx at a time.
*/
list_sort(NULL, &rq_list, sched_rq_cmp);
do {
dispatched |= blk_mq_dispatch_hctx_list(&rq_list);
} while (!list_empty(&rq_list));
} else {
dispatched = blk_mq_dispatch_rq_list(hctx, &rq_list, count);
}
if (busy)
return -EAGAIN;
return !!dispatched;
}
static int blk_mq_do_dispatch_sched(struct blk_mq_hw_ctx *hctx)
{
int ret;
do {
ret = __blk_mq_do_dispatch_sched(hctx);
} while (ret == 1);
return ret;
}
static struct blk_mq_ctx *blk_mq_next_ctx(struct blk_mq_hw_ctx *hctx,
struct blk_mq_ctx *ctx)
{
unsigned short idx = ctx->index_hw[hctx->type];
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.
*
* Returns -EAGAIN if hctx->dispatch was found non-empty and run_work has to
* be run again. This is necessary to avoid starving flushes.
*/
static int 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);
int ret = 0;
struct request *rq;
do {
int budget_token;
if (!list_empty_careful(&hctx->dispatch)) {
ret = -EAGAIN;
break;
}
if (!sbitmap_any_bit_set(&hctx->ctx_map))
break;
budget_token = blk_mq_get_dispatch_budget(q);
if (budget_token < 0)
break;
rq = blk_mq_dequeue_from_ctx(hctx, ctx);
if (!rq) {
blk_mq_put_dispatch_budget(q, budget_token);
/*
* We're releasing without dispatching. Holding the
* budget could have blocked any "hctx"s with the
* same queue and if we didn't dispatch then there's
* no guarantee anyone will kick the queue. Kick it
* ourselves.
*/
blk_mq_delay_run_hw_queues(q, BLK_MQ_BUDGET_DELAY);
break;
}
blk_mq_set_rq_budget_token(rq, budget_token);
/*
* 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(rq->mq_hctx, &rq_list, 1));
WRITE_ONCE(hctx->dispatch_from, ctx);
return ret;
}
static int __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.dispatch_request;
int ret = 0;
LIST_HEAD(rq_list);
/*
* 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(hctx, &rq_list, 0)) {
if (has_sched_dispatch)
ret = blk_mq_do_dispatch_sched(hctx);
else
ret = blk_mq_do_dispatch_ctx(hctx);
}
} else if (has_sched_dispatch) {
ret = blk_mq_do_dispatch_sched(hctx);
} else if (hctx->dispatch_busy) {
/* dequeue request one by one from sw queue if queue is busy */
ret = blk_mq_do_dispatch_ctx(hctx);
} else {
blk_mq_flush_busy_ctxs(hctx, &rq_list);
blk_mq_dispatch_rq_list(hctx, &rq_list, 0);
}
return ret;
}
void blk_mq_sched_dispatch_requests(struct blk_mq_hw_ctx *hctx)
{
struct request_queue *q = hctx->queue;
/* 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++;
/*
* A return of -EAGAIN is an indication that hctx->dispatch is not
* empty and we must run again in order to avoid starving flushes.
*/
if (__blk_mq_sched_dispatch_requests(hctx) == -EAGAIN) {
if (__blk_mq_sched_dispatch_requests(hctx) == -EAGAIN)
blk_mq_run_hw_queue(hctx, true);
}
}
bool __blk_mq_sched_bio_merge(struct request_queue *q, struct bio *bio,
unsigned int nr_segs)
{
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, bio->bi_opf, ctx);
bool ret = false;
enum hctx_type type;
if (e && e->type->ops.bio_merge)
return e->type->ops.bio_merge(hctx, bio, nr_segs);
type = hctx->type;
if (!(hctx->flags & BLK_MQ_F_SHOULD_MERGE) ||
list_empty_careful(&ctx->rq_lists[type]))
return false;
/* default per sw-queue merge */
spin_lock(&ctx->lock);
/*
* 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.
*/
if (blk_bio_list_merge(q, &ctx->rq_lists[type], bio, nr_segs)) {
ctx->rq_merged++;
ret = true;
}
spin_unlock(&ctx->lock);
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);
static bool blk_mq_sched_bypass_insert(struct blk_mq_hw_ctx *hctx,
bool has_sched,
struct request *rq)
{
/*
* dispatch flush and passthrough rq directly
*
* passthrough request has to be added to hctx->dispatch directly.
* For some reason, device may be in one situation which can't
* handle FS request, so STS_RESOURCE is always returned and the
* FS request will be added to hctx->dispatch. However passthrough
* request may be required at that time for fixing the problem. If
* passthrough request is added to scheduler queue, there isn't any
* chance to dispatch it given we prioritize requests in hctx->dispatch.
*/
if ((rq->rq_flags & RQF_FLUSH_SEQ) || blk_rq_is_passthrough(rq))
return true;
if (has_sched)
rq->rq_flags |= RQF_SORTED;
return false;
}
void blk_mq_sched_insert_request(struct request *rq, bool at_head,
bool run_queue, bool async)
{
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 = rq->mq_hctx;
WARN_ON(e && (rq->tag != BLK_MQ_NO_TAG));
if (blk_mq_sched_bypass_insert(hctx, !!e, rq)) {
/*
* Firstly normal IO request is inserted to scheduler queue or
* sw queue, meantime we add flush request to dispatch queue(
* hctx->dispatch) directly and there is at most one in-flight
* flush request for each hw queue, so it doesn't matter to add
* flush request to tail or front of the dispatch queue.
*
* Secondly in case of NCQ, flush request belongs to non-NCQ
* command, and queueing it will fail when there is any
* in-flight normal IO request(NCQ command). When adding flush
* rq to the front of hctx->dispatch, it is easier to introduce
* extra time to flush rq's latency because of S_SCHED_RESTART
* compared with adding to the tail of dispatch queue, then
* chance of flush merge is increased, and less flush requests
* will be issued to controller. It is observed that ~10% time
* is saved in blktests block/004 on disk attached to AHCI/NCQ
* drive when adding flush rq to the front of hctx->dispatch.
*
* Simply queue flush rq to the front of hctx->dispatch so that
* intensive flush workloads can benefit in case of NCQ HW.
*/
at_head = (rq->rq_flags & RQF_FLUSH_SEQ) ? true : at_head;
blk_mq_request_bypass_insert(rq, at_head, false);
goto run;
}
if (e && e->type->ops.insert_requests) {
LIST_HEAD(list);
list_add(&rq->queuelist, &list);
e->type->ops.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 blk_mq_hw_ctx *hctx,
struct blk_mq_ctx *ctx,
struct list_head *list, bool run_queue_async)
{
struct elevator_queue *e;
struct request_queue *q = hctx->queue;
/*
* blk_mq_sched_insert_requests() is called from flush plug
* context only, and hold one usage counter to prevent queue
* from being released.
*/
percpu_ref_get(&q->q_usage_counter);
e = hctx->queue->elevator;
if (e && e->type->ops.insert_requests)
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 && !e && !run_queue_async) {
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 void blk_mq_sched_free_tags(struct blk_mq_tag_set *set,
struct blk_mq_hw_ctx *hctx,
unsigned int hctx_idx)
{
unsigned int flags = set->flags & ~BLK_MQ_F_TAG_HCTX_SHARED;
if (hctx->sched_tags) {
blk_mq_free_rqs(set, hctx->sched_tags, hctx_idx);
blk_mq_free_rq_map(hctx->sched_tags, flags);
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;
/* Clear HCTX_SHARED so tags are init'ed */
unsigned int flags = set->flags & ~BLK_MQ_F_TAG_HCTX_SHARED;
int ret;
hctx->sched_tags = blk_mq_alloc_rq_map(set, hctx_idx, q->nr_requests,
set->reserved_tags, flags);
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;
}
/* called in queue's release handler, tagset has gone away */
static void blk_mq_sched_tags_teardown(struct request_queue *q)
{
struct blk_mq_hw_ctx *hctx;
int i;
queue_for_each_hw_ctx(q, hctx, i) {
/* Clear HCTX_SHARED so tags are freed */
unsigned int flags = hctx->flags & ~BLK_MQ_F_TAG_HCTX_SHARED;
if (hctx->sched_tags) {
blk_mq_free_rq_map(hctx->sched_tags, flags);
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;
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;
}