linux-kernel - Re: [Bug #12809] iozone regression with 2.6.29-rc6

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Date:	Thu, 5 Mar 2009 09:09:20 +0800
From:	Wu Fengguang <fengguang.wu@...el.com>
To:	"Rafael J. Wysocki" <rjw@...k.pl>
Cc:	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Kernel Testers List <kernel-testers@...r.kernel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	"Lin, Ming M" <ming.m.lin@...el.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Nick Piggin <npiggin@...e.de>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>
Subject: Re: [Bug #12809] iozone regression with 2.6.29-rc6

On Tue, Mar 03, 2009 at 09:25:59PM +0200, Rafael J. Wysocki wrote:
> This message has been generated automatically as a part of a report
> of recent regressions.
> 
> The following bug entry is on the current list of known regressions
> from 2.6.28.  Please verify if it still should be listed and let me know
> (either way).
> 
> 
> Bug-Entry	: http://bugzilla.kernel.org/show_bug.cgi?id=12809
> Subject		: iozone regression with 2.6.29-rc6
> Submitter	: Lin Ming <ming.m.lin@...el.com>
> Date		: 2009-02-27 9:13 (5 days old)
> First-Bad-Commit: http://git.kernel.org/?p=linux/kernel/git/torvalds/linux-2.6.git;a=commit;h=1cf6e7d83bf334cc5916137862c920a97aabc018
> References	: http://marc.info/?l=linux-kernel&m=123572630504360&w=4
> Handled-By	: Wu Fengguang <fengguang.wu@...el.com>

Following Peter's idea of relaxing writeback throttling, Lin Ming
and I tried the idea of totally disabling writeback throttling by
doing benchmarks with the following parameters:

        echo 60 > /proc/sys/vm/dirty_ratio
        echo 50 > /proc/sys/vm/dirty_background_ratio

The result is encouraging: the iozone performance is restored to the
level of 2.6.29-rc5!

We'll continue to evaluate the dirty/throttling numbers with Nick's patch.

Thanks,
Fengguang
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