linux-kernel - Re: [PATCH 1/3] thermal/cpu-cooling, sched/core: Cleanup thermal pressure definition

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Date:   Mon, 22 Jun 2020 10:22:42 +0200
From:   Vincent Guittot <vincent.guittot@...aro.org>
To:     Ionela Voinescu <ionela.voinescu@....com>
Cc:     Valentin Schneider <valentin.schneider@....com>,
        Juri Lelli <juri.lelli@...hat.com>,
        "open list:THERMAL" <linux-pm@...r.kernel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Viresh Kumar <viresh.kumar@...aro.org>,
        Amit Daniel Kachhap <amit.kachhap@...il.com>,
        Daniel Lezcano <daniel.lezcano@...aro.org>,
        Russell King <linux@...linux.org.uk>,
        Thara Gopinath <thara.gopinath@...aro.org>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        Sudeep Holla <sudeep.holla@....com>,
        Dietmar Eggemann <dietmar.eggemann@....com>,
        Ingo Molnar <mingo@...nel.org>,
        LAK <linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH 1/3] thermal/cpu-cooling, sched/core: Cleanup thermal
 pressure definition

On Sat, 20 Jun 2020 at 19:49, Ionela Voinescu <ionela.voinescu@....com> wrote:
>
> Hi Vincent,
>
> On Thursday 18 Jun 2020 at 17:03:24 (+0200), Vincent Guittot wrote:
> > On Sun, 14 Jun 2020 at 03:10, Valentin Schneider
> > <valentin.schneider@....com> wrote:
> [..]
> > > diff --git a/drivers/thermal/cpufreq_cooling.c b/drivers/thermal/cpufreq_cooling.c
> > > index e297e135c031..a1efd379b683 100644
> > > --- a/drivers/thermal/cpufreq_cooling.c
> > > +++ b/drivers/thermal/cpufreq_cooling.c
> > > @@ -417,6 +417,11 @@ static int cpufreq_get_cur_state(struct thermal_cooling_device *cdev,
> > >         return 0;
> > >  }
> > >
> > > +__weak void
> > > +arch_set_thermal_pressure(const struct cpumask *cpus, unsigned long th_pressure)
> > > +{
> > > +}
> >
> > Having this weak function declared in cpufreq_cooling is weird. This
> > means that we will have to do so for each one that wants to use it.
> >
> > Can't you declare an empty function in a common header file ?
>
> Do we expect anyone other than cpufreq_cooling to call
> arch_set_thermal_pressure()?

Yes, cpufreq cooling device is only 1 possible way to do thermal mitigation

>
> I'm not against any of the options, either having it here as a week
> default definition (same as done for arch_set_freq_scale() in cpufreq.c)
> or in a common header (as done for arch_scale_freq_capacity() in sched.h).
>
> But for me, Valentin's implementation seems more natural as setters are
> usually only called from within the framework that does the control
> (throttling for thermal or frequency setting for cpufreq) and we
> probably want to think twice if we want to call them from other places.
>
> Thanks,
> Ionela.