From 9a0e609e3fd8a95c96629b9fbde6b8c5b9a1456a Mon Sep 17 00:00:00 2001 From: Mike Snitzer Date: Tue, 24 Feb 2015 11:03:22 -0500 Subject: [PATCH] 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: Mike Snitzer --- drivers/md/dm.c | 12 +++++++++--- 1 file changed, 9 insertions(+), 3 deletions(-) diff --git a/drivers/md/dm.c b/drivers/md/dm.c index 43e0d1a85a60..7924c00e0716 100644 --- a/drivers/md/dm.c +++ b/drivers/md/dm.c @@ -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) - blk_run_queue_async(md->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 -- 2.20.1