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Date: Thu, 3 Dec 2009 11:53:30 +0800 From: Shaohua Li <shaohua.li@...el.com> To: linux-kernel@...r.kernel.org Cc: jens.axboe@...cle.com, akpm@...ux-foundation.org Subject: [RFC]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 <shaohua.li@...el.com> diff --git a/block/cfq-iosched.c b/block/cfq-iosched.c index aa1e953..e05650f 100644 --- a/block/cfq-iosched.c +++ b/block/cfq-iosched.c @@ -1298,9 +1298,9 @@ 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; } /* -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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