From 7cedffec8e759480f7f7a9be9cd0d7ebf0aafff2 Mon Sep 17 00:00:00 2001 From: Bart Van Assche Date: Wed, 26 Sep 2018 14:01:09 -0700 Subject: block: Make blk_get_request() block for non-PM requests while suspended 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 Reviewed-by: Ming Lei Reviewed-by: Christoph Hellwig Cc: Jianchao Wang Cc: Hannes Reinecke Cc: Johannes Thumshirn Cc: Alan Stern Signed-off-by: Jens Axboe --- block/blk-pm.c | 44 +++++++++++++++++++++++++++++++++++++++----- 1 file changed, 39 insertions(+), 5 deletions(-) (limited to 'block/blk-pm.c') diff --git a/block/blk-pm.c b/block/blk-pm.c index 9b636960d285..972fbc656846 100644 --- a/block/blk-pm.c +++ b/block/blk-pm.c @@ -1,8 +1,11 @@ // SPDX-License-Identifier: GPL-2.0 +#include #include #include #include +#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; + 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 (q->nr_pending) { - ret = -EBUSY; + 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); -- cgit v1.2.3