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

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Date:   Wed, 10 Oct 2018 14:50:33 +0200
From:   Juri Lelli <juri.lelli@...il.com>
To:     Vincent Guittot <vincent.guittot@...aro.org>
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 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..