linux-kernel - Re: iozone write 50% regression in kernel 2.6.24-rc1

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Date:	Mon, 12 Nov 2007 08:45:57 +0800
From:	"Zhang, Yanmin" <yanmin_zhang@...ux.intel.com>
To:	Martin Knoblauch <knobi@...bisoft.de>
Cc:	a.p.zijlstra@...llo.nl, LKML <linux-kernel@...r.kernel.org>
Subject: Re: iozone write 50% regression in kernel 2.6.24-rc1

On Fri, 2007-11-09 at 04:36 -0800, Martin Knoblauch wrote:
> ----- Original Message ----
> > From: "Zhang, Yanmin" <yanmin_zhang@...ux.intel.com>
> > To: a.p.zijlstra@...llo.nl
> > Cc: LKML <linux-kernel@...r.kernel.org>
> > Sent: Friday, November 9, 2007 10:47:52 AM
> > Subject: iozone write 50% regression in kernel 2.6.24-rc1
> > 
> > Comparing with 2.6.23, iozone sequential write/rewrite (512M) has
> > 50%
> > 
>  regression
> > in kernel 2.6.24-rc1. 2.6.24-rc2 has the same regression.
> > 
> > My machine has 8 processor cores and 8GB memory.
> > 
> > By bisect, I located patch
> > http://git.kernel.org/?p=linux/kernel/git/torvalds/linux-2.6.git;a=commitdiff;h=
> > 04fbfdc14e5f48463820d6b9807daa5e9c92c51f.
> > 
> > 
> > Another behavior: with kernel 2.6.23, if I run iozone for many
> > times
> > 
>  after rebooting machine,
> > the result looks stable. But with 2.6.24-rc1, the first run of
> > iozone
> > 
>  got a very small result and
> > following run has 4Xorig_result.
> > 
> > What I reported is the regression of 2nd/3rd run, because first run
> > has
> > 
>  bigger regression.
> > 
> > I also tried to change
> > /proc/sys/vm/dirty_ratio,dirty_backgroud_ratio
> > 
>  and didn't get improvement.
>  could you tell us the exact iozone command you are using?
iozone -i 0 -r 4k -s 512m


>  I would like to repeat it on my setup, because I definitely see the opposite behaviour in 2.6.24-rc1/rc2. The speed there is much better than in 2.6.22 and before (I skipped 2.6.23, because I was waiting for the per-bdi changes). I definitely do not see the difference between 1st and subsequent runs. But then, I do my tests with 5GB file sizes like:
> 
> iozone3_283/src/current/iozone -t 5 -F /scratch/X1 /scratch/X2 /scratch/X3 /scratch/X4 /scratch/X5 -s 5000M -r 1024 -c -e -i 0 -i 1
My machine uses SATA (AHCI) disk.

-yanmin
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