linux-kernel - Re: [RFC PATCH 0/7] Introduce thermal pressure

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Date:   Wed, 10 Oct 2018 15:08:52 +0200
From:   Vincent Guittot <vincent.guittot@...aro.org>
To:     Juri Lelli <juri.lelli@...il.com>
Cc:     Quentin Perret <quentin.perret@....com>,
        Ingo Molnar <mingo@...nel.org>,
        Thara Gopinath <thara.gopinath@...aro.org>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        Ingo Molnar <mingo@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Zhang Rui <rui.zhang@...el.com>,
        "gregkh@...uxfoundation.org" <gregkh@...uxfoundation.org>,
        "Rafael J. Wysocki" <rafael@...nel.org>,
        Amit Kachhap <amit.kachhap@...il.com>,
        viresh kumar <viresh.kumar@...aro.org>,
        Javi Merino <javi.merino@...nel.org>,
        Eduardo Valentin <edubezval@...il.com>,
        Daniel Lezcano <daniel.lezcano@...aro.org>,
        "open list:THERMAL" <linux-pm@...r.kernel.org>,
        Ionela Voinescu <ionela.voinescu@....com>
Subject: Re: [RFC PATCH 0/7] Introduce thermal pressure

On Wed, 10 Oct 2018 at 14:50, Juri Lelli <juri.lelli@...il.com> wrote:
>
> On 10/10/18 14:34, Vincent Guittot wrote:
> > Hi  Juri,
> >
> > On Wed, 10 Oct 2018 at 14:23, Juri Lelli <juri.lelli@...il.com> wrote:
> > >
> > > On 10/10/18 14:04, Vincent Guittot wrote:
> > >
> > > [...]
> > >
> > > > The problem was the same with RT, the cfs utilization was lower than
> > > > reality because RT steals soem cycle to CFS
> > > > So schedutil was selecting a lower frequency when cfs was running
> > > > whereas the CPU was fully used.
> > > > The same can happen with thermal:
> > > > cap the max freq because of thermal
> > > > the utilization with decrease.
> > > > remove the cap
> > > > the utilization is still low and you will select a low OPP because you
> > > > don't take into account cycle stolen by thermal like with RT
> > >
> > > What if we scale frequency component considering the capped temporary
> > > max?
> >
> > Do you mean using a kind of scale_thermal_capacity in accumulate_sum
> > when computing utilization ?
>
> Yeah, something like that I guess. So that we account for temporary
> "fake" 1024..

But the utilization will not be invariant anymore across the system