linux-kernel - Re: scheduler vs hardware? (was Re: another i7 (linux) bug?)

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Date:	Sat, 23 Jan 2010 10:43:15 +0100
From:	Ingo Molnar <mingo@...e.hu>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	Mike Galbraith <efault@....de>, Luca Zini <luca.zini@...il.com>,
	aagaande@...il.com, rdelcueto@...mail.com,
	linux-kernel <linux-kernel@...r.kernel.org>,
	Alex Chiang <achiang@...com>
Subject: Re: scheduler vs hardware? (was Re: another i7  (linux) bug?)


* Peter Zijlstra <peterz@...radead.org> wrote:

> On Fri, 2010-01-22 at 08:19 +0100, Mike Galbraith wrote:
> > > if I run a cpu intensive process with the lowest priority (19
> > > from man nice) I obtain much better performance that with the
> > > highest priority available (-20 from man nice).
> > >
> > > For example the same file is processed by lame in 8.7 seconds
> > > at the lowest priority, and in 12 seconds at the highest
> > > priority.  Before posting a bug I wold like to understand if
> > > this is a problem related to the i7 mobile (my processor is a
> > > i7 Q720).
> > > 
> > > As far as I tested on the same laptop series (dell studio 15),
> > > with the same kernel this problem does not exists.
> > 
> > So you only see this on the i7.  That's odd.  Can you try 33-rc5?
> > 
> > Posting a reliable reproducer would be nice.  It'd also be nice to see
> > what all is running when you see this, and where.
> 
> Using a sample from: http://lame.sourceforge.net/quality.php
> 
> My laptop does:
> 
> 
> # time nice -n 19 lame -b 256 -V0 -h youcantdothat.wav - > /dev/null

A 'perf stat --repeat 3' run would tell us more about the underlying reasons i 
think.

	Ingo
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