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@xxxxxxxxxx>
---
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 6a85bd4..8e58df5 100644
--- a/drivers/md/dm.c
+++ b/drivers/md/dm.c
@@ -1021,10 +1021,13 @@ 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);
/*
@@ -1033,8 +1036,11 @@ 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
--
1.9.3 (Apple Git-50)
--
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