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

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Message-Id: <20090508120119.8c93cfd7.akpm@linux-foundation.org>
Date:	Fri, 8 May 2009 12:01:19 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Jeff Moyer <jmoyer@...hat.com>
Cc:	linux-kernel@...r.kernel.org, jens.axboe@...cle.com,
	"Rafael J. Wysocki" <rjw@...k.pl>
Subject: Re: 2.6.30-rc deadline scheduler performance regression for iozone
 over NFS

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.

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