linux-kernel - Re: [Patch v8 4/7] sched/fair: Enable periodic update of average thermal pressure

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Date:   Mon, 27 Jan 2020 16:15:04 +0100
From:   Vincent Guittot <vincent.guittot@...aro.org>
To:     Dietmar Eggemann <dietmar.eggemann@....com>
Cc:     Peter Zijlstra <peterz@...radead.org>,
        Thara Gopinath <thara.gopinath@...aro.org>,
        Ingo Molnar <mingo@...hat.com>,
        Ionela Voinescu <ionela.voinescu@....com>,
        Zhang Rui <rui.zhang@...el.com>,
        Quentin Perret <qperret@...gle.com>,
        Daniel Lezcano <daniel.lezcano@...aro.org>,
        viresh kumar <viresh.kumar@...aro.org>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        Amit Kachhap <amit.kachhap@...il.com>,
        Javi Merino <javi.merino@...nel.org>,
        Amit Kucheria <amit.kucheria@...durent.com>
Subject: Re: [Patch v8 4/7] sched/fair: Enable periodic update of average
 thermal pressure

On Mon, 27 Jan 2020 at 13:09, Dietmar Eggemann <dietmar.eggemann@....com> wrote:
>
> On 24/01/2020 16:45, Vincent Guittot wrote:
> > On Fri, 24 Jan 2020 at 16:37, Dietmar Eggemann <dietmar.eggemann@....com> wrote:
> >>
> >> On 17/01/2020 16:39, Vincent Guittot wrote:
> >>> On Fri, 17 Jan 2020 at 15:55, Peter Zijlstra <peterz@...radead.org> wrote:
> >>>>
> >>>> On Fri, Jan 17, 2020 at 02:22:51PM +0100, Vincent Guittot wrote:
> >>>>> On Thu, 16 Jan 2020 at 16:15, Peter Zijlstra <peterz@...radead.org> wrote:
>
> [...]
>
> >> The 'now' argument is one thing but why not:
> >>
> >> -int update_thermal_load_avg(u64 now, struct rq *rq, u64 capacity)
> >> +int update_thermal_load_avg(u64 now, struct rq *rq)
> >>  {
> >> +       u64 capacity = arch_cpu_thermal_pressure(cpu_of(rq));
> >> +
> >>         if (___update_load_sum(now, &rq->avg_thermal,
> >>
> >> This would make the call-sites __update_blocked_others() and
> >> task_tick(_fair)() cleaner.
> >
> > I prefer to keep the capacity as argument. This is more aligned with
> > others that provides the value of the signal to apply
> >
> >>
> >> I guess the argument is not to pollute pelt.c. But it already contains
> >
> > you've got it. I don't want to pollute the pelt.c file with things not
> > related to pelt but thermal as an example.
> >
> >> arch_scale_[freq|cpu]_capacity() for irq.
>
> But isn't arch_cpu_thermal_pressure() not exactly the same as
> arch_scale_cpu_capacity() and arch_scale_freq_capacity()?
>
> All of them are defined by default within the scheduler code
> [include/linux/sched/topology.h or kernel/sched/sched.h] and can be
> overwritten by arch code with a fast implementation (e.g. returning a
> per-cpu variable).
>
> So why is using arch_scale_freq_capacity() and arch_scale_cpu_capacity()
> in update_irq_load_avg [kernel/sched/pelt.c] and update_rq_clock_pelt()

As explained previously, update_irq_load_avg is an exception and not
the example to follow. update_rt/dl_rq_load_avg are the example to
follow and fixing update_irq_load_avg exception is on my todo list

> [kernel/sched/pelt.h] OK but arch_cpu_thermal_pressure() in
> update_thermal_load_avg() [kernel/sched/pelt.c] not?
>
> Shouldn't arch_cpu_thermal_pressure() not be called
> arch_scale_thermal_capacity() to highlight the fact that those three

Quoted from cover letter https://lkml.org/lkml/2020/1/14/1164:
"
v6->v7:
       - ...
        - Renamed arch_scale_thermal_capacity to arch_cpu_thermal_pressure
          as per review comments from Peter, Dietmar and Ionela.
       -...

"

> functions are doing the same thing, scaling capacity by something (cpu,
> frequency or thermal)?