Subject: Re: [announce] CFS-devel, performance improvements
From: Peter Zijlstra <peterz@infradead.org>
To: Roman Zippel <zippel@linux-m68k.org>
Cc: Ingo Molnar <mingo@elte.hu>, linux-kernel@vger.kernel.org,
       Mike Galbraith <efault@gmx.de>
In-Reply-To: <1189703165.21778.258.camel@twins>
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Date: Thu, 13 Sep 2007 19:09:42 +0200
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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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