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dm: only run the queue on completion if congested or no requests pending

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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 <snitzer@redhat.com>
This commit is contained in:
Mike Snitzer 2015-02-24 11:03:22 -05:00
parent ff36ab3458
commit 9a0e609e3f
1 changed files with 9 additions and 3 deletions
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12
drivers/md/dm.c
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@ -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