Re: [announce] CFS-devel, performance improvements

Peter Zijlstra
2007-09-13T17:06:18Z

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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

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