Commit 474b18cc authored Dec 03, 2009 by Shaohua Li Committed by Jens Axboe Dec 03, 2009

cfq-iosched: no dispatch limit for single queue



Since commit 2f5cb738, each queue can send
up to 4 * 4 requests if only one queue exists. I wonder why we have such limit.
Device supports tag can send more requests. For example, AHCI can send 31
requests. Test (direct aio randread) shows the limits reduce about 4% disk
thoughput.
On the other hand, since we send one request one time, if other queue
pop when current is sending more than cfq_quantum requests, current queue will
stop send requests soon after one request, so sounds there is no big latency.

Signed-off-by: Shaohua Li <shaohua.li@intel.com>
Signed-off-by: Jens Axboe <jens.axboe@oracle.com>

parent 98262f27

block/cfq-iosched.c

+2 −2

Original line number	Diff line number	Diff line
		@@ -1618,9 +1618,9 @@ static bool cfq_may_dispatch(struct cfq_data cfqd, struct cfq_queue cfqq)
		return false;

		/*
		* Sole queue user, allow bigger slice
		* Sole queue user, no limit
		*/
		max_dispatch *= 4;
		max_dispatch = -1;
		}

		/*