linux-kernel - Re: [PATCH v6 04/11] cpufreq/schedutil: use rt utilization tracking

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Message-ID: <20180622114426.GC2512@hirez.programming.kicks-ass.net>
Date:   Fri, 22 Jun 2018 13:44:26 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Quentin Perret <quentin.perret@....com>
Cc:     Vincent Guittot <vincent.guittot@...aro.org>, mingo@...nel.org,
        linux-kernel@...r.kernel.org, rjw@...ysocki.net,
        juri.lelli@...hat.com, dietmar.eggemann@....com,
        Morten.Rasmussen@....com, viresh.kumar@...aro.org,
        valentin.schneider@....com, patrick.bellasi@....com,
        joel@...lfernandes.org, daniel.lezcano@...aro.org,
        Ingo Molnar <mingo@...hat.com>
Subject: Re: [PATCH v6 04/11] cpufreq/schedutil: use rt utilization tracking

On Fri, Jun 22, 2018 at 01:37:13PM +0200, Peter Zijlstra wrote:
> I suppose we can make it more complicated, something like:
> 
>              u           u
>   f := u + (--- - u) * (---)^n
>             1-r         1-r
> 
> Where: u := cfs util
>        r := \Sum !cfs util
>        f := frequency request
> 
> That would still satisfy all criteria I think:
> 
>   r = 0      -> f := u
>   u = (1-r)  -> f := 1
> 
> and in particular:
> 
>   u << (1-r) -> f ~= u
> 
> which casuses less inflation than the linear thing where there is idle
> time.

Note that for n=0 this last property is lost and we have the initial
linear case back.