linux/block/blk-mq-sched.c
Shin'ichiro Kawasaki 572299f03a block: limit request dispatch loop duration
When IO requests are made continuously and the target block device
handles requests faster than request arrival, the request dispatch loop
keeps on repeating to dispatch the arriving requests very long time,
more than a minute. Since the loop runs as a workqueue worker task, the
very long loop duration triggers workqueue watchdog timeout and BUG [1].

To avoid the very long loop duration, break the loop periodically. When
opportunity to dispatch requests still exists, check need_resched(). If
need_resched() returns true, the dispatch loop already consumed its time
slice, then reschedule the dispatch work and break the loop. With heavy
IO load, need_resched() does not return true for 20~30 seconds. To cover
such case, check time spent in the dispatch loop with jiffies. If more
than 1 second is spent, reschedule the dispatch work and break the loop.

[1]

[  609.691437] BUG: workqueue lockup - pool cpus=10 node=1 flags=0x0 nice=-20 stuck for 35s!
[  609.701820] Showing busy workqueues and worker pools:
[  609.707915] workqueue events: flags=0x0
[  609.712615]   pwq 0: cpus=0 node=0 flags=0x0 nice=0 active=1/256 refcnt=2
[  609.712626]     pending: drm_fb_helper_damage_work [drm_kms_helper]
[  609.712687] workqueue events_freezable: flags=0x4
[  609.732943]   pwq 0: cpus=0 node=0 flags=0x0 nice=0 active=1/256 refcnt=2
[  609.732952]     pending: pci_pme_list_scan
[  609.732968] workqueue events_power_efficient: flags=0x80
[  609.751947]   pwq 0: cpus=0 node=0 flags=0x0 nice=0 active=1/256 refcnt=2
[  609.751955]     pending: neigh_managed_work
[  609.752018] workqueue kblockd: flags=0x18
[  609.769480]   pwq 21: cpus=10 node=1 flags=0x0 nice=-20 active=3/256 refcnt=4
[  609.769488]     in-flight: 1020:blk_mq_run_work_fn
[  609.769498]     pending: blk_mq_timeout_work, blk_mq_run_work_fn
[  609.769744] pool 21: cpus=10 node=1 flags=0x0 nice=-20 hung=35s workers=2 idle: 67
[  639.899730] BUG: workqueue lockup - pool cpus=10 node=1 flags=0x0 nice=-20 stuck for 66s!
[  639.909513] Showing busy workqueues and worker pools:
[  639.915404] workqueue events: flags=0x0
[  639.920197]   pwq 0: cpus=0 node=0 flags=0x0 nice=0 active=1/256 refcnt=2
[  639.920215]     pending: drm_fb_helper_damage_work [drm_kms_helper]
[  639.920365] workqueue kblockd: flags=0x18
[  639.939932]   pwq 21: cpus=10 node=1 flags=0x0 nice=-20 active=3/256 refcnt=4
[  639.939942]     in-flight: 1020:blk_mq_run_work_fn
[  639.939955]     pending: blk_mq_timeout_work, blk_mq_run_work_fn
[  639.940212] pool 21: cpus=10 node=1 flags=0x0 nice=-20 hung=66s workers=2 idle: 67

Fixes: 6e6fcbc27e ("blk-mq: support batching dispatch in case of io")
Signed-off-by: Shin'ichiro Kawasaki <shinichiro.kawasaki@wdc.com>
Cc: stable@vger.kernel.org # v5.10+
Link: https://lore.kernel.org/linux-block/20220310091649.zypaem5lkyfadymg@shindev/
Link: https://lore.kernel.org/r/20220318022641.133484-1-shinichiro.kawasaki@wdc.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>
2022-03-17 20:31:43 -06:00

663 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"
/*
* 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)
{
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, const struct list_head *a,
const 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);
count++;
if (rq->mq_hctx != hctx)
multi_hctxs = true;
/*
* If we cannot get tag for the request, stop dequeueing
* requests from the IO scheduler. We are unlikely to be able
* to submit them anyway and it creates false impression for
* scheduling heuristics that the device can take more IO.
*/
if (!blk_mq_get_driver_tag(rq))
break;
} 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)
{
unsigned long end = jiffies + HZ;
int ret;
do {
ret = __blk_mq_do_dispatch_sched(hctx);
if (ret != 1)
break;
if (need_resched() || time_is_before_jiffies(end)) {
blk_mq_delay_run_hw_queue(hctx, 0);
break;
}
} while (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;
const bool has_sched = q->elevator;
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)
ret = blk_mq_do_dispatch_sched(hctx);
else
ret = blk_mq_do_dispatch_ctx(hctx);
}
} else if (has_sched) {
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;
struct blk_mq_hw_ctx *hctx;
bool ret = false;
enum hctx_type type;
if (e && e->type->ops.bio_merge) {
ret = e->type->ops.bio_merge(q, bio, nr_segs);
goto out_put;
}
ctx = blk_mq_get_ctx(q);
hctx = blk_mq_map_queue(q, bio->bi_opf, ctx);
type = hctx->type;
if (!(hctx->flags & BLK_MQ_F_SHOULD_MERGE) ||
list_empty_careful(&ctx->rq_lists[type]))
goto out_put;
/* 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))
ret = true;
spin_unlock(&ctx->lock);
out_put:
return ret;
}
bool blk_mq_sched_try_insert_merge(struct request_queue *q, struct request *rq,
struct list_head *free)
{
return rq_mergeable(rq) && elv_attempt_insert_merge(q, rq, free);
}
EXPORT_SYMBOL_GPL(blk_mq_sched_try_insert_merge);
static bool blk_mq_sched_bypass_insert(struct blk_mq_hw_ctx *hctx,
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;
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, 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) {
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(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) {
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;
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_rqs(q);
blk_mq_exit_sched(q, eq);
kobject_put(&eq->kobj);
return ret;
}
}
blk_mq_debugfs_register_sched_hctx(q, hctx);
}
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) {
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;
}
flags = hctx->flags;
}
blk_mq_debugfs_unregister_sched(q);
if (e->type->ops.exit_sched)
e->type->ops.exit_sched(e);
blk_mq_sched_tags_teardown(q, flags);
q->elevator = NULL;
}