linux-kernel - Re: Performance regression in IO scheduler still there

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Date:	Thu, 12 Nov 2009 18:29:41 +0100
From:	Jan Kara <jack@...e.cz>
To:	Jeff Moyer <jmoyer@...hat.com>
Cc:	Jan Kara <jack@...e.cz>, jens.axboe@...cle.com,
	LKML <linux-kernel@...r.kernel.org>,
	Chris Mason <chris.mason@...cle.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Mike Galbraith <efault@....de>, mszeredi@...e.de
Subject: Re: Performance regression in IO scheduler still there

On Wed 11-11-09 12:43:30, Jeff Moyer wrote:
> Jan Kara <jack@...e.cz> writes:
> 
> >   Sadly, I don't see the improvement you can see :(. The numbers are the
> > same regardless low_latency set to 0:
> > 2.6.32-rc5 low_latency = 0:
> > 37.39 36.43 36.51 -> 36.776667 0.434920
> >   But my testing environment is a plain SATA drive so that probably
> > explains the difference...
> 
> I just retested (10 runs for each kernel) on a SATA disk with no NCQ
> support and I could not see a difference.  I'll try to dig up a disk
> that support NCQ.  Is that what you're using for testing?
  I don't think I am. How do I find out?

>               2.6.29    2.6.32-rc6,low_latency=0
> ----------------------------------
> Average:      34.6648   34.4475
> Pop.Std.Dev.: 0.55523   0.21981
  Hmm, strange. Miklos Szeredi tried tiobench on his machine and he also
saw the regression. I'll try to think what could make the difference.

								Honza
-- 
Jan Kara <jack@...e.cz>
SUSE Labs, CR
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