linux-kernel - Re: Epic regression in throughput since v2.6.23

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Date:	Thu, 10 Sep 2009 08:53:06 +0200
From:	Ingo Molnar <mingo@...e.hu>
To:	Serge Belyshev <belyshev@...ni.sinp.msu.ru>
Cc:	Con Kolivas <kernel@...ivas.org>, linux-kernel@...r.kernel.org,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Mike Galbraith <efault@....de>
Subject: Re: Epic regression in throughput since v2.6.23

* Serge Belyshev <belyshev@...ni.sinp.msu.ru> wrote:

> Ingo Molnar <mingo@...e.hu> writes:
> 
> > Thanks!
> >
> > I think we found the reason for that regression - would you mind 
> > to re-test with latest -tip, e157986 or later?
> >
> > If that works for you i'll describe our theory.
> >
> 
> Good job -- seems to work, thanks.  Regression is still about 3% 
> though: http://img3.imageshack.us/img3/5335/epicbfstip.png

Ok, thanks for the update. The problem is that i've run out of 
testsystems that can reproduce this. So we need your help to debug 
this directly ...

A good start would be to post the -tip versus BFS "perf stat" 
measurement results:

   perf stat --repeat 3 make -j4 bzImage

And also the -j8 perf stat result, so that we can see what the 
difference is between -j4 and -j8.

Note: please check out latest tip and do:

  cd tools/perf/
  make -j install

To pick up the latest 'perf' tool. In particular the precision of 
--repeat has been improved recently so you want that binary from 
-tip even if you measure vanilla .31 or .31 based BFS.

Also, it would be nice if you could send me your kernel config - 
maybe it's some config detail that keeps me from being able to 
reproduce these results. I havent seen a link to a config in your 
mails (maybe i missed it - these threads are voluminous).

	Ingo
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