linux-kernel - Re: aim7 -30% regression in 2.6.24-rc1

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Date:	Tue, 30 Oct 2007 10:12:05 +0800
From:	"Zhang, Yanmin" <yanmin_zhang@...ux.intel.com>
To:	Ingo Molnar <mingo@...e.hu>
Cc:	LKML <linux-kernel@...r.kernel.org>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>
Subject: Re: aim7 -30% regression in 2.6.24-rc1

On Mon, 2007-10-29 at 17:37 +0800, Zhang, Yanmin wrote:
> On Mon, 2007-10-29 at 10:22 +0800, Zhang, Yanmin wrote:
> > On Fri, 2007-10-26 at 13:23 +0200, Ingo Molnar wrote:
> > > * Zhang, Yanmin <yanmin_zhang@...ux.intel.com> wrote:
> > > 
> > > > I tested 2.6.24-rc1 on my x86_64 machine which has 2 quad-core processors.
> > > > 
> > > > Comparing with 2.6.23, aim7 has about -30% regression. I did a bisect 
> > > > and found patch 
> > > > http://git.kernel.org/?p=linux/kernel/git/torvalds/linux-2.6.git;a=commitdiff;h=b5869ce7f68b233ceb81465a7644be0d9a5f3dbb 
> > > > caused the issue.
> > > 
> > > weird, that's a commit diff - i.e. it changes no code.
> > I got the tag from #git log. As for above link, I just added prior http address,
> > so readers could check the patch by clicking.
> > 
> > > 
> > > > kbuild/SPECjbb2000/SPECjbb2005 also has big regressions. On my another 
> > > > tigerton machine (4 quad-core processors), SPECjbb2005 has more than 
> > > > -40% regression. I didn't do a bisect on such benchmark testing, but I 
> > > > suspect the root cause is like aim7's.
> > > 
> > > these two commits might be relevant:
> > > 
> > >   7a6c6bcee029a978f866511d6e41dbc7301fde4c
> > I did a quick testing. This patch has no impact.
> > 
> > >   95dbb421d12fdd9796ed153853daf3679809274f
> > Above big patch doesn't include this one, which means if I do
> > 'git checkout b5869ce7f68b233ceb81465a7644be0d9a5f3dbb', the kernel doesn't include
> > 95dbb421d12fdd9796ed153853daf3679809274f.
> > 
> > > 
> > > but a bisection result would be the best info.
> > I will do a bisect between 2.6.23 and tag 9c63d9c021f375a2708ad79043d6f4dd1291a085.
> I ran git bisect with kernel version as the tag. It looks like git will
> be crazy sometimes. So I checked ChangeLog and used the number tag to replace
> the kernel version and retested it.
> 
> It looks like at least 2 patches were responsible for the regression. I'm
> doing sub-bisect now.
> 
> I could find aim7 regression on all my testing machines although the regression
> percentage is different.
> 
> Machine					regression
> 8-core stoakley				30%
> 16-core tigerton			6%
> tulsa(dual-core+HT, 16 logical cpu)	20%
sub-bisecting captured patch 38ad464d410dadceda1563f36bdb0be7fe4c8938(sched: uniform tunings)
caused 20% regression of aim7.

The last 10% should be also related to sched parameters, such like
sysctl_sched_min_granularity.

-yanmin
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