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

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Date:	Wed, 11 Nov 2009 12:43:30 -0500
From:	Jeff Moyer <jmoyer@...hat.com>
To:	Jan Kara <jack@...e.cz>
Cc:	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>
Subject: Re: Performance regression in IO scheduler still there

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?

Cheers,
Jeff

              2.6.29    2.6.32-rc6,low_latency=0
----------------------------------
Average:      34.6648   34.4475
Pop.Std.Dev.: 0.55523   0.21981
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