linux-kernel - Re: 2.6.30-rc deadline scheduler performance regression for iozone over NFS

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Message-ID: <x49skjb21b7.fsf@segfault.boston.devel.redhat.com>
Date:	Mon, 11 May 2009 09:53:32 -0400
From:	Jeff Moyer <jmoyer@...hat.com>
To:	Jens Axboe <jens.axboe@...cle.com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	linux-kernel@...r.kernel.org, "Rafael J. Wysocki" <rjw@...k.pl>
Subject: Re: 2.6.30-rc deadline scheduler performance regression for iozone over NFS

Jens Axboe <jens.axboe@...cle.com> writes:

> On Fri, May 08 2009, Andrew Morton wrote:
>> On Thu, 23 Apr 2009 10:01:58 -0400
>> Jeff Moyer <jmoyer@...hat.com> wrote:
>> 
>> > Hi,
>> > 
>> > I've been working on CFQ improvements for interleaved I/Os between
>> > processes, and noticed a regression in performance when using the
>> > deadline I/O scheduler.  The test uses a server configured with a cciss
>> > array and 1Gb/s ethernet.
>> > 
>> > The iozone command line was:
>> >   iozone -s 2000000 -r 64 -f /mnt/test/testfile -i 1 -w
>> > 
>> > The numbers in the nfsd's row represent the number of nfsd "threads".
>> > These numbers (in MB/s) represent the average of 5 runs.
>> > 
>> >                v2.6.29
>> > 
>> > nfsd's  |   1    |  2   |   4   |   8
>> > --------+---------------+-------+------
>> > deadline| 43207 | 67436 | 96289 | 107590
>> > 
>> >               2.6.30-rc1
>> > 
>> > nfsd's  |   1   |   2   |   4   |   8
>> > --------+---------------+-------+------
>> > deadline| 43732 | 68059 | 76659 | 83231
>> > 
>> >     2.6.30-rc3.block-for-linus
>> > 
>> > nfsd's  |   1   |   2   |   4   |   8
>> > --------+---------------+-------+------
>> > deadline| 46102 | 71151 | 83120 | 82330
>> > 
>> > 
>> > Notice the drop for 4 and 8 threads.  It may be worth noting that the
>> > default number of NFSD threads is 8.
>> > 
>> 
>> I guess we should ask Rafael to add this to the post-2.6.29 regression
>> list.
>
> I agree. It'd be nice to bisect this one down, I'm guessing some mm
> change has caused this writeout regression.

It's not writeout, it's a read test.

Cheers,
Jeff
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