linux-kernel - Re: [Bug #11308] tbench regression on each kernel release from 2.6.22 -> 2.6.28

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Date:	Mon, 17 Nov 2008 01:14:03 -0800 (PST)
From:	David Miller <davem@...emloft.net>
To:	mingo@...e.hu
Cc:	rjw@...k.pl, linux-kernel@...r.kernel.org,
	kernel-testers@...r.kernel.org, cl@...ux-foundation.org,
	efault@....de, a.p.zijlstra@...llo.nl
Subject: Re: [Bug #11308] tbench regression on each kernel release from
 2.6.22 -&gt; 2.6.28

From: Ingo Molnar <mingo@...e.hu>
Date: Mon, 17 Nov 2008 10:06:48 +0100

> 
> * Rafael J. Wysocki <rjw@...k.pl> wrote:
> 
> > This message has been generated automatically as a part of a report
> > of regressions introduced between 2.6.26 and 2.6.27.
> > 
> > The following bug entry is on the current list of known regressions
> > introduced between 2.6.26 and 2.6.27.  Please verify if it still should
> > be listed and let me know (either way).
> > 
> > 
> > Bug-Entry	: http://bugzilla.kernel.org/show_bug.cgi?id=11308
> > Subject		: tbench regression on each kernel release from  2.6.22 -&gt; 2.6.28
> > Submitter	: Christoph Lameter <cl@...ux-foundation.org>
> > Date		: 2008-08-11 18:36 (98 days old)
> > References	: http://marc.info/?l=linux-kernel&m=121847986119495&w=4
> > 		  http://marc.info/?l=linux-kernel&m=122125737421332&w=4
> 
> Christoph, as per the recent analysis of Mike:
> 
>  http://fixunix.com/kernel/556867-regression-benchmark-throughput-loss-a622cf6-f7160c7-pull.html
> 
> all scheduler components of this regression have been eliminated.
> 
> In fact his numbers show that scheduler speedups since 2.6.22 have 
> offset and hidden most other sources of tbench regression. (i.e. the 
> scheduler portion got 5% faster, hence it was able to offset a 
> slowdown of 5% in other areas of the kernel that tbench triggers)

Although I respect the improvements, wake_up() is still several orders
of magnitude slower than it was in 2.6.22 and wake_up() is at the top
of the profiles in tbench runs.

It really is premature to close this regression at this time.

I am working with every spare moment I have to try and nail this
stuff, but unless someone else helps me people need to be patient.
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