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blk-mq: make mq_queue_reinit_notify() freeze queues in parallel 

q->mq_usage_counter is a percpu_ref which is killed and drained when
the queue is frozen.  On a CPU hotplug event, blk_mq_queue_reinit()
which involves freezing the queue is invoked on all existing queues.
Because percpu_ref killing and draining involve a RCU grace period,
doing the above on one queue after another may take a long time if
there are many queues on the system.

This patch splits out initiation of freezing and waiting for its
completion, and updates blk_mq_queue_reinit_notify() so that the
queues are frozen in parallel instead of one after another.  Note that
freezing and unfreezing are moved from blk_mq_queue_reinit() to
blk_mq_queue_reinit_notify().

Signed-off-by: Tejun Heo <tj@kernel.org>
Reported-by: Christian Borntraeger <borntraeger@de.ibm.com>
Tested-by: Christian Borntraeger <borntraeger@de.ibm.com>
Signed-off-by: Jens Axboe <axboe@fb.com>
This commit is contained in:
Tejun Heo 2014-11-04 13:52:27 -05:00 committed by Jens Axboe
parent ece9c72acc
commit f3af020b9a
1 changed files with 33 additions and 8 deletions
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41
block/blk-mq.c
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@ -107,11 +107,7 @@ static void blk_mq_usage_counter_release(struct percpu_ref *ref)
wake_up_all(&q->mq_freeze_wq); wake_up_all(&q->mq_freeze_wq);
} }
/* static void blk_mq_freeze_queue_start(struct request_queue *q)
* Guarantee no request is in use, so we can change any data structure of
* the queue afterward.
*/
void blk_mq_freeze_queue(struct request_queue *q)
{ {
bool freeze; bool freeze;
@ -123,9 +119,23 @@ void blk_mq_freeze_queue(struct request_queue *q)
percpu_ref_kill(&q->mq_usage_counter); percpu_ref_kill(&q->mq_usage_counter);
blk_mq_run_queues(q, false); blk_mq_run_queues(q, false);
} }
}
static void blk_mq_freeze_queue_wait(struct request_queue *q)
{
wait_event(q->mq_freeze_wq, percpu_ref_is_zero(&q->mq_usage_counter)); wait_event(q->mq_freeze_wq, percpu_ref_is_zero(&q->mq_usage_counter));
} }
/*
* Guarantee no request is in use, so we can change any data structure of
* the queue afterward.
*/
void blk_mq_freeze_queue(struct request_queue *q)
{
blk_mq_freeze_queue_start(q);
blk_mq_freeze_queue_wait(q);
}
static void blk_mq_unfreeze_queue(struct request_queue *q) static void blk_mq_unfreeze_queue(struct request_queue *q)
{ {
bool wake; bool wake;
@ -1921,7 +1931,7 @@ void blk_mq_free_queue(struct request_queue *q)
/* Basically redo blk_mq_init_queue with queue frozen */ /* Basically redo blk_mq_init_queue with queue frozen */
static void blk_mq_queue_reinit(struct request_queue *q) static void blk_mq_queue_reinit(struct request_queue *q)
{ {
blk_mq_freeze_queue(q); WARN_ON_ONCE(!q->mq_freeze_depth);
blk_mq_sysfs_unregister(q); blk_mq_sysfs_unregister(q);
@ -1936,8 +1946,6 @@ static void blk_mq_queue_reinit(struct request_queue *q)
blk_mq_map_swqueue(q); blk_mq_map_swqueue(q);
blk_mq_sysfs_register(q); blk_mq_sysfs_register(q);
blk_mq_unfreeze_queue(q);
} }
static int blk_mq_queue_reinit_notify(struct notifier_block *nb, static int blk_mq_queue_reinit_notify(struct notifier_block *nb,
@ -1956,8 +1964,25 @@ static int blk_mq_queue_reinit_notify(struct notifier_block *nb,
return NOTIFY_OK; return NOTIFY_OK;
mutex_lock(&all_q_mutex); mutex_lock(&all_q_mutex);
/*
* We need to freeze and reinit all existing queues. Freezing
* involves synchronous wait for an RCU grace period and doing it
* one by one may take a long time. Start freezing all queues in
* one swoop and then wait for the completions so that freezing can
* take place in parallel.
*/
list_for_each_entry(q, &all_q_list, all_q_node)
blk_mq_freeze_queue_start(q);
list_for_each_entry(q, &all_q_list, all_q_node)
blk_mq_freeze_queue_wait(q);
list_for_each_entry(q, &all_q_list, all_q_node) list_for_each_entry(q, &all_q_list, all_q_node)
blk_mq_queue_reinit(q); blk_mq_queue_reinit(q);
list_for_each_entry(q, &all_q_list, all_q_node)
blk_mq_unfreeze_queue(q);
mutex_unlock(&all_q_mutex); mutex_unlock(&all_q_mutex);
return NOTIFY_OK; return NOTIFY_OK;
} }