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

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Date:	Mon, 11 May 2009 18:58:26 +0200
From:	Jens Axboe <jens.axboe@...cle.com>
To:	Jeff Moyer <jmoyer@...hat.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

On Mon, May 11 2009, Jeff Moyer wrote:
> 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.

Doh sorry, I even ran these tests as well a few weeks back. So perhaps
some read-ahead change, I didn't look into it. FWIW, on a single SATA
drive here, it didn't show any difference.

-- 
Jens Axboe

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