linux-kernel - Re: [PATCH v5 08/10] cpufreq/schedutil: take into account interrupt

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Date:   Mon, 28 May 2018 14:37:30 +0200
From:   Juri Lelli <juri.lelli@...hat.com>
To:     Vincent Guittot <vincent.guittot@...aro.org>
Cc:     Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...nel.org>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        "Rafael J. Wysocki" <rjw@...ysocki.net>,
        Dietmar Eggemann <dietmar.eggemann@....com>,
        Morten Rasmussen <Morten.Rasmussen@....com>,
        viresh kumar <viresh.kumar@...aro.org>,
        Valentin Schneider <valentin.schneider@....com>,
        Quentin Perret <quentin.perret@....com>
Subject: Re: [PATCH v5 08/10] cpufreq/schedutil: take into account interrupt

On 28/05/18 14:06, Vincent Guittot wrote:
> Hi Juri,
> 
> On 28 May 2018 at 12:41, Juri Lelli <juri.lelli@...hat.com> wrote:
> > Hi Vincent,
> >
> > On 25/05/18 15:12, Vincent Guittot wrote:
> >> The time spent under interrupt can be significant but it is not reflected
> >> in the utilization of CPU when deciding to choose an OPP. Now that we have
> >> access to this metric, schedutil can take it into account when selecting
> >> the OPP for a CPU.
> >> The CPU utilization is :
> >>   irq util_avg + (1 - irq util_avg / max capacity ) * /Sum rq util_avg
> >
> > IIUC the code below you actually propose that
> >
> >  util = [(max_cap - util_irq) * util_rq] / max_cap + util_irq
> >
> > where
> >
> >  util_rq  = /Sum rq util_avg
> >  util_irq = irq util_avg
> >
> > So, which one is what you have in mind? Or am I wrong? :)
> 
> mmh ... aren't they equal  ?
> 
> util = [(max_cap - util_irq) * util_rq] / max_cap + util_irq
> util = [(max_cap/max_cap - util_irq/max_cap) * util_rq]  + util_irq
> util = [(1 - util_irq/max_cap) * util_rq]  + util_irq
> util = util_irq +  [(1 - util_irq/max_cap) * util_rq]

Ah, indeed.