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| author | Jan Kara <jack@suse.cz> | 2016-06-28 09:04:01 +0200 |
|---|---|---|
| committer | Jens Axboe <axboe@fb.com> | 2016-06-28 08:21:48 -0600 |
| commit | 149321a611d5d41cebcf5f813a3bf45b3afe66ad (patch) | |
| tree | 55b2dcd151cd40b622c2c5e41d29d6cb1f38960e /block | |
| parent | 93fdf1478aaba6c397ba54f4cc534bf5019831b4 (diff) | |
| download | linux-149321a611d5d41cebcf5f813a3bf45b3afe66ad.tar.bz2 | |
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>
Diffstat (limited to 'block')
| -rw-r--r-- | block/cfq-iosched.c | 11 |
1 files changed, 10 insertions, 1 deletions
diff --git a/block/cfq-iosched.c b/block/cfq-iosched.c index c1adbd01d0fa..2d03004dc77c 100644 --- a/block/cfq-iosched.c +++ b/block/cfq-iosched.c @@ -4243,7 +4243,16 @@ static void cfq_completed_request(struct request_queue *q, struct request *rq) cfqq_type(cfqq)); st->ttime.last_end_request = now; - if (!(rq->start_time + cfqd->cfq_fifo_expire[1] > now)) + /* + * We have to do this check in jiffies since start_time is in + * jiffies and it is not trivial to convert to ns. If + * cfq_fifo_expire[1] ever comes close to 1 jiffie, this test + * will become problematic but so far we are fine (the default + * is 128 ms). + */ + if (!time_after(rq->start_time + + nsecs_to_jiffies(cfqd->cfq_fifo_expire[1]), + jiffies)) cfqd->last_delayed_sync = now; } |