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

[Jens Axboe <jens.axboe@oracle.com>]

On Fri, May 08 2009, Andrew Morton wrote:
> On Thu, 23 Apr 2009 10:01:58 -0400
> Jeff Moyer <jmoyer@redhat.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.

-- 
Jens Axboe