cfq-iosched: Fix regression in bonnie++ rewrite performance
authorJan Kara <jack@suse.cz>
Tue, 28 Jun 2016 07:04:01 +0000 (09:04 +0200)
committerJens Axboe <axboe@fb.com>
Tue, 28 Jun 2016 14:21:48 +0000 (08:21 -0600)
commit149321a611d5d41cebcf5f813a3bf45b3afe66ad
tree55b2dcd151cd40b622c2c5e41d29d6cb1f38960e
parent93fdf1478aaba6c397ba54f4cc534bf5019831b4
cfq-iosched: Fix regression in bonnie++ rewrite performance

Commit 9a7f38c42c2 (cfq-iosched: Convert from jiffies to nanoseconds)
broke the condition for detecting starved sync IO in
cfq_completed_request() because rq->start_time remained in jiffies but
we compared it with nanosecond values. This manifested as a regression
in bonnie++ rewrite performance because we always ended up considering
sync IO starved and thus never increased async IO queue depth.

Since rq->start_time is used in a lot of places, converting it to ns
values would be non-trivial. So just revert the condition in CFQ to use
comparison with jiffies. This will lead to suboptimal results if
cfq_fifo_expire[1] will ever come close to 1 jiffie but so far we are
relatively far from that with the storage used with CFQ (the default
value is 128 ms).

Fixes: 9a7f38c42c2b92391d9dabaf9f51df7cfe5608e4
Signed-off-by: Jan Kara <jack@suse.cz>
Signed-off-by: Jens Axboe <axboe@fb.com>
block/cfq-iosched.c