[PATCH 2/2] bfq: Allow short_ttime queues to have waker

[Jan Kara <jack@suse.cz>]

Currently queues that have average think time shorter than slice_idle
cannot have waker. However this requirement is too strict. E.g. dbench
process always submits a one or two IOs (which is enough to pull its
average think time below slice_idle) and then blocks waiting for jbd2
thread to commit a transaction. Due to idling logic jbd2 thread is
often forced to wait for dbench's idle timer to trigger to be able to
submit its IO and this severely delays the overall benchmark progress.

E.g. on my test machine current dbench single-thread throughput is ~80
MB/s, with this patch it is ~200 MB/s.

Signed-off-by: Jan Kara <jack@suse.cz>
---
 block/bfq-iosched.c | 1 -
 1 file changed, 1 deletion(-)

diff --git a/block/bfq-iosched.c b/block/bfq-iosched.c
index 18f85d474c9c..416473ba80c8 100644
--- a/block/bfq-iosched.c
+++ b/block/bfq-iosched.c
@@ -1928,7 +1928,6 @@ static void bfq_add_request(struct request *rq)
 		 * I/O-plugging interval for bfqq.
 		 */
 		if (bfqd->last_completed_rq_bfqq &&
-		    !bfq_bfqq_has_short_ttime(bfqq) &&
 		    ktime_get_ns() - bfqd->last_completion <
 		    200 * NSEC_PER_USEC) {
 			if (bfqd->last_completed_rq_bfqq != bfqq &&
-- 
2.16.4