Commit 8e1ac665 authored Nov 08, 2010 by Shaohua Li Committed by Jens Axboe Nov 08, 2010

cfq-iosched: don't idle if a deep seek queue is slow

If a deep seek queue slowly deliver requests but disk is much faster, idle
for the queue just wastes disk throughput. If the queue delevers all requests
before half its slice is used, the patch disable idle for it.
In my test, application delivers 32 requests one time, the disk can accept
128 requests at maxium and disk is fast. without the patch, the throughput
is just around 30m/s, while with it, the speed is about 80m/s. The disk is
a SSD, but is detected as a rotational disk. I can configure it as SSD, but
I thought the deep seek queue logic should be fixed too, for example,
considering a fast raid.

Signed-off-by: Shaohua Li <shaohua.li@intel.com>
Signed-off-by: Jens Axboe <jaxboe@fusionio.com>

parent d2d59e18

block/cfq-iosched.c

+11 −0

Original line number	Diff line number	Diff line
		@@ -2285,6 +2285,17 @@ static struct cfq_queue cfq_select_queue(struct cfq_data cfqd)
		goto keep_queue;
		}

		/*
		* This is a deep seek queue, but the device is much faster than
		* the queue can deliver, don't idle
		**/
		if (CFQQ_SEEKY(cfqq) && cfq_cfqq_idle_window(cfqq) &&
		(cfq_cfqq_slice_new(cfqq) \|\|
		(cfqq->slice_end - jiffies > jiffies - cfqq->slice_start))) {
		cfq_clear_cfqq_deep(cfqq);
		cfq_clear_cfqq_idle_window(cfqq);
		}

		if (cfqq->dispatched && cfq_should_idle(cfqd, cfqq)) {
		cfqq = NULL;
		goto keep_queue;

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