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>
diff --git a/block/cfq-iosched.c b/block/cfq-iosched.c
index c1adbd0..2d03004 100644
--- a/block/cfq-iosched.c
+++ b/block/cfq-iosched.c
@@ -4243,7 +4243,16 @@
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;
}