From 474b18ccc264c472abeec50f48469b6477202699 Mon Sep 17 00:00:00 2001 From: Shaohua Li Date: Thu, 3 Dec 2009 12:58:05 +0100 Subject: cfq-iosched: no dispatch limit for single queue Since commit 2f5cb7381b737e24c8046fd4aeab571fb71315f5, 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 Signed-off-by: Jens Axboe --- block/cfq-iosched.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) (limited to 'block') diff --git a/block/cfq-iosched.c b/block/cfq-iosched.c index 71446497d7b6..f5b59e18ebd3 100644 --- a/block/cfq-iosched.c +++ b/block/cfq-iosched.c @@ -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; } /* -- cgit v1.2.3-59-g8ed1b