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block: Make blk_get_request() block for non-PM requests while suspended

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Instead of allowing requests that are not power management requests
to enter the queue in runtime suspended status (RPM_SUSPENDED), make
the blk_get_request() caller block. This change fixes a starvation
issue: it is now guaranteed that power management requests will be
executed no matter how many blk_get_request() callers are waiting.
For blk-mq, instead of maintaining the q->nr_pending counter, rely
on q->q_usage_counter. Call pm_runtime_mark_last_busy() every time a
request finishes instead of only if the queue depth drops to zero.

Signed-off-by: Bart Van Assche <bvanassche@acm.org>
Reviewed-by: Ming Lei <ming.lei@redhat.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Cc: Jianchao Wang <jianchao.w.wang@oracle.com>
Cc: Hannes Reinecke <hare@suse.com>
Cc: Johannes Thumshirn <jthumshirn@suse.de>
Cc: Alan Stern <stern@rowland.harvard.edu>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
This commit is contained in:
Bart Van Assche 2018-09-26 14:01:09 -07:00 committed by Jens Axboe
parent bdd6316094
commit 7cedffec8e
2 changed files with 47 additions and 34 deletions
repo.diff.show_diff_stats Download patch file Download diff file Expand all files Collapse all files

35
block/blk-core.c
View file

@ -2746,30 +2746,6 @@ void blk_account_io_done(struct request *req, u64 now)
}
}
#ifdef CONFIG_PM
/*
* Don't process normal requests when queue is suspended
* or in the process of suspending/resuming
*/
static bool blk_pm_allow_request(struct request *rq)
{
switch (rq->q->rpm_status) {
case RPM_RESUMING:
case RPM_SUSPENDING:
return rq->rq_flags & RQF_PM;
case RPM_SUSPENDED:
return false;
default:
return true;
}
}
#else
static bool blk_pm_allow_request(struct request *rq)
{
return true;
}
#endif
void blk_account_io_start(struct request *rq, bool new_io)
{
struct hd_struct *part;
@ -2815,11 +2791,14 @@ static struct request *elv_next_request(struct request_queue *q)
while (1) {
list_for_each_entry(rq, &q->queue_head, queuelist) {
if (blk_pm_allow_request(rq))
#ifdef CONFIG_PM
/*
* If a request gets queued in state RPM_SUSPENDED
* then that's a kernel bug.
*/
WARN_ON_ONCE(q->rpm_status == RPM_SUSPENDED);
#endif
return rq;
if (rq->rq_flags & RQF_SOFTBARRIER)
break;
}
/*

44
block/blk-pm.c
View file

@ -1,8 +1,11 @@
// SPDX-License-Identifier: GPL-2.0
#include <linux/blk-mq.h>
#include <linux/blk-pm.h>
#include <linux/blkdev.h>
#include <linux/pm_runtime.h>
#include "blk-mq.h"
#include "blk-mq-tag.h"
/**
* blk_pm_runtime_init - Block layer runtime PM initialization routine
@ -68,14 +71,40 @@ int blk_pre_runtime_suspend(struct request_queue *q)
if (!q->dev)
return ret;
spin_lock_irq(q->queue_lock);
if (q->nr_pending) {
WARN_ON_ONCE(q->rpm_status != RPM_ACTIVE);
/*
* Increase the pm_only counter before checking whether any
* non-PM blk_queue_enter() calls are in progress to avoid that any
* new non-PM blk_queue_enter() calls succeed before the pm_only
* counter is decreased again.
*/
blk_set_pm_only(q);
ret = -EBUSY;
/* Switch q_usage_counter from per-cpu to atomic mode. */
blk_freeze_queue_start(q);
/*
* Wait until atomic mode has been reached. Since that
* involves calling call_rcu(), it is guaranteed that later
* blk_queue_enter() calls see the pm-only state. See also
* http://lwn.net/Articles/573497/.
*/
percpu_ref_switch_to_atomic_sync(&q->q_usage_counter);
if (percpu_ref_is_zero(&q->q_usage_counter))
ret = 0;
/* Switch q_usage_counter back to per-cpu mode. */
blk_mq_unfreeze_queue(q);
spin_lock_irq(q->queue_lock);
if (ret < 0)
pm_runtime_mark_last_busy(q->dev);
} else {
else
q->rpm_status = RPM_SUSPENDING;
}
spin_unlock_irq(q->queue_lock);
if (ret)
blk_clear_pm_only(q);
return ret;
}
EXPORT_SYMBOL(blk_pre_runtime_suspend);
@ -106,6 +135,9 @@ void blk_post_runtime_suspend(struct request_queue *q, int err)
pm_runtime_mark_last_busy(q->dev);
}
spin_unlock_irq(q->queue_lock);
if (err)
blk_clear_pm_only(q);
}
EXPORT_SYMBOL(blk_post_runtime_suspend);
@ -153,13 +185,15 @@ void blk_post_runtime_resume(struct request_queue *q, int err)
spin_lock_irq(q->queue_lock);
if (!err) {
q->rpm_status = RPM_ACTIVE;
__blk_run_queue(q);
pm_runtime_mark_last_busy(q->dev);
pm_request_autosuspend(q->dev);
} else {
q->rpm_status = RPM_SUSPENDED;
}
spin_unlock_irq(q->queue_lock);
if (!err)
blk_clear_pm_only(q);
}
EXPORT_SYMBOL(blk_post_runtime_resume);