Re: [RFC PATCH 0/7] sched: cpufreq: Remove magic margins

Peter Zijlstra
2023-09-08T13:58:56Z

On Fri, Sep 08, 2023 at 02:33:36PM +0100, Qais Yousef wrote:

> > > UTIL_EST_FASTER moves in one direction. And it's a constant response too, no?
> >
> > The idea of UTIL_EST_FASTER was that we run a PELT sum on the current
> > activation runtime, all runtime since wakeup and take the max of this
> > extra sum and the regular thing.
> >
> > On top of that this extra PELT sum can/has a time multiplier and thus
> > ramps up faster (this multiplies could be per task). Nb.:
> >
> > util_est_fast = faster_est_approx(delta * 2);
> >
> > is a state-less expression -- by making
> >
> > util_est_fast = faster_est_approx(delta * curr->se.faster_mult);
> >
> > only the current task is affected.
>
> Okay; maybe I didn't understand this fully and will go back and study it more.
>
> Maybe the word faster is what makes me worried as I really see faster is not
> what people want on a class of systems; or at least CPUs if you think of HMP.
> Taming the beast is a more difficult problem in this class of systems.

The faster refers to the ramp-up. Which was the issue identified in that
earlier thread. The game thing wanted to ramp up more agressive.