linux-kernel - Re: CFS review

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Message-Id: <1186730615.19991.12.camel@Homer.simpson.net>
Date:	Fri, 10 Aug 2007 09:23:35 +0200
From:	Mike Galbraith <efault@....de>
To:	Roman Zippel <zippel@...ux-m68k.org>
Cc:	Ingo Molnar <mingo@...e.hu>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Andi Kleen <andi@...stfloor.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	linux-kernel@...r.kernel.org
Subject: Re: CFS review

On Fri, 2007-08-10 at 01:14 +0200, Roman Zippel wrote:
> Hi,

Greetings,

> On Wed, 1 Aug 2007, Ingo Molnar wrote:
> 
> > just to make sure, how does 'top' output of the l + "lt 3" testcase look 
> > like now on your laptop? Yesterday it was this:
> > 
> >  4544 roman     20   0  1796  520  432 S 32.1  0.4   0:21.08 lt
> >  4545 roman     20   0  1796  344  256 R 32.1  0.3   0:21.07 lt
> >  4546 roman     20   0  1796  344  256 R 31.7  0.3   0:21.07 lt
> >  4547 roman     20   0  1532  272  216 R  3.3  0.2   0:01.94 l
> > 
> > and i'm still wondering how that output was possible.
> 
> I disabled the jiffies logic and the result is still the same, so this 
> problem isn't related to resolution at all.
> I traced it a little and what's happing is that the busy loop really only 
> gets little time, it only runs inbetween the timer tasks. When the timer 
> task is woken up __enqueue_sleeper() updates sleeper_bonus and a little 
> later when the busy loop is preempted __update_curr() is called a last 
> time and it's fully hit by the sleeper_bonus. So the timer tasks use less 
> time than they actually get and thus produce overflows, the busy loop OTOH 
> is punished and underflows.

I still can't reproduce this here.  Can you please send your .config, so
I can try again with a config as close to yours as possible?

	-Mike

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