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

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Message-ID: <x49hc0f79k9.fsf@segfault.boston.devel.redhat.com>
Date:	Thu, 23 Apr 2009 10:01:58 -0400
From:	Jeff Moyer <jmoyer@...hat.com>
To:	linux-kernel@...r.kernel.org
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Jens Axboe <jens.axboe@...cle.com>
Subject: 2.6.30-rc deadline scheduler performance regression for iozone over NFS

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.

Cheers,
Jeff
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