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@xxxxxxx> --- block/cfq-iosched.c | 11 ++++++++++- 1 file changed, 10 insertions(+), 1 deletion(-) diff --git a/block/cfq-iosched.c b/block/cfq-iosched.c index 98cece4e62a9..e074dd4f1384 100644 --- a/block/cfq-iosched.c +++ b/block/cfq-iosched.c @@ -4233,7 +4233,16 @@ 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; } -- 2.6.6 -- To unsubscribe from this list: send the line "unsubscribe linux-block" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
