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

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Date:   Wed, 10 Oct 2018 15:34:43 +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 15:08, Vincent Guittot wrote:
> 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

Mmm, I guess I might be wrong, but I was thinking we should be able to
deal with this similarly to what we do with cpus with different max
capacities. So, another factor?  Because then, how do we handle other
ways in which max freq can be restricted (e.g. from userspace as Javi
was also mentioning)?