linux-kernel - Re: [announce] CFS-devel, performance improvements

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Message-Id: <1189703382.21778.260.camel@twins>
Date:	Thu, 13 Sep 2007 19:09:42 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Roman Zippel <zippel@...ux-m68k.org>
Cc:	Ingo Molnar <mingo@...e.hu>, linux-kernel@...r.kernel.org,
	Mike Galbraith <efault@....de>
Subject: Re: [announce] CFS-devel, performance improvements

On Thu, 2007-09-13 at 19:06 +0200, Peter Zijlstra wrote:
> On Thu, 2007-09-13 at 18:50 +0200, Roman Zippel wrote:
> 
> > I never claimed to understand every detail of CFS, I can _guess_ what 
> > _might_ have been intended, but from that it's impossible to know for 
> > certain how important they are. Let's take this patch fragment:
> > 
> 
> 	delta_fair = se->delta_fair_sleep;
> 
> we slept that much
> 
> > -       /*
> > -        * Fix up delta_fair with the effect of us running
> > -        * during the whole sleep period:
> > -        */
> > -       if (sched_feat(SLEEPER_AVG))
> > -               delta_fair = div64_likely32((u64)delta_fair * load,
> > -                                               load + se->load.weight);
> 
> if we would have ran we would not have been removed from the rq and the
> weight would have been: rq_weight + weight
> 
> so compensate for us having been removed from the rq by scaling the
> delta with: rq_weight/(rq_weight + weight)
> 
> > -       delta_fair = calc_weighted(delta_fair, se);
> 
> scale for nice levels
> 

Or at least, I think that is how to read it :-)

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