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Commit 9a0e609e authored by Mike Snitzer's avatar Mike Snitzer
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dm: only run the queue on completion if congested or no requests pending 



On really fast storage it can be beneficial to delay running the
request_queue to allow the elevator more opportunity to merge requests.

Otherwise, it has been observed that requests are being sent to
q->request_fn much quicker than is ideal on IOPS-bound backends.

Signed-off-by: default avatarMike Snitzer <snitzer@redhat.com>
parent ff36ab34

drivers/md/dm.c

+9 −3
Original line number Diff line number Diff line
@@ -1024,10 +1024,13 @@ static void end_clone_bio(struct bio *clone, int error) 
 */

static void rq_completed(struct mapped_device *md, int rw, bool run_queue)

{

	int nr_requests_pending;



	atomic_dec(&md->pending[rw]);



	/* nudge anyone waiting on suspend queue */

	if (!md_in_flight(md))

	nr_requests_pending = md_in_flight(md);

	if (!nr_requests_pending)

		wake_up(&md->wait);



	/*
@@ -1036,8 +1039,11 @@ static void rq_completed(struct mapped_device *md, int rw, bool run_queue) 
	 * back into ->request_fn() could deadlock attempting to grab the

	 * queue lock again.

	 */

	if (run_queue)

	if (run_queue) {

		if (!nr_requests_pending ||

		    (nr_requests_pending >= md->queue->nr_congestion_on))

			blk_run_queue_async(md->queue);

	}



	/*

	 * dm_put() must be at the end of this function. See the comment above