linux-kernel - Re: Do not overload dispatch queue (Was: Re: IO scheduler based IO controller V10)

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Date:	Sun, 04 Oct 2009 13:33:33 +0200
From:	Mike Galbraith <efault@....de>
To:	Jens Axboe <jens.axboe@...cle.com>
Cc:	Vivek Goyal <vgoyal@...hat.com>, Ingo Molnar <mingo@...e.hu>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Ulrich Lukas <stellplatz-nr.13a@...enparkplatz.de>,
	linux-kernel@...r.kernel.org,
	containers@...ts.linux-foundation.org, dm-devel@...hat.com,
	nauman@...gle.com, dpshah@...gle.com, lizf@...fujitsu.com,
	mikew@...gle.com, fchecconi@...il.com, paolo.valente@...more.it,
	ryov@...inux.co.jp, fernando@....ntt.co.jp, jmoyer@...hat.com,
	dhaval@...ux.vnet.ibm.com, balbir@...ux.vnet.ibm.com,
	righi.andrea@...il.com, m-ikeda@...jp.nec.com, agk@...hat.com,
	akpm@...ux-foundation.org, peterz@...radead.org,
	jmarchan@...hat.com, riel@...hat.com
Subject: Re: Do not overload dispatch queue (Was: Re: IO scheduler based IO
 controller V10)

Wrong one.  Let's try the post java version instead.

8e29675: "implement slower async initiate and queue ramp up" introduced a
throughput regression for concurrent reader vs writer.  Adjusting async delay
to use cfq_slice_async restored throughput.

Signed-off-by: Mike Galbraith <efault@....de>

---
 block/cfq-iosched.c |    7 ++++---
 1 file changed, 4 insertions(+), 3 deletions(-)

Index: linux-2.6/block/cfq-iosched.c
===================================================================
--- linux-2.6.orig/block/cfq-iosched.c
+++ linux-2.6/block/cfq-iosched.c
@@ -1343,17 +1343,18 @@ static int cfq_dispatch_requests(struct
 	 */
 	if (!cfq_cfqq_sync(cfqq) && cfqd->cfq_desktop) {
 		unsigned long last_sync = jiffies - cfqd->last_end_sync_rq;
+		unsigned long slice = cfq_slice_async;
 		unsigned int depth;
 
 		/*
 		 * must wait a bit longer
 		 */
-		if (last_sync < cfq_slice_sync) {
-			cfq_schedule_dispatch(cfqd, cfq_slice_sync - last_sync);
+		if (last_sync < slice) {
+			cfq_schedule_dispatch(cfqd, slice - last_sync);
 			return 0;
 		}
 
-		depth = last_sync / cfq_slice_sync;
+		depth = last_sync / slice;
 		if (depth < max_dispatch)
 			max_dispatch = depth;
 	}


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