linux-kernel - Re: [PATCH v4 08/16] sched/core: uclamp: propagate parent clamps

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Date:   Wed, 12 Sep 2018 08:56:22 -0700
From:   Suren Baghdasaryan <surenb@...gle.com>
To:     Patrick Bellasi <patrick.bellasi@....com>
Cc:     LKML <linux-kernel@...r.kernel.org>, linux-pm@...r.kernel.org,
        Ingo Molnar <mingo@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Tejun Heo <tj@...nel.org>,
        "Rafael J . Wysocki" <rafael.j.wysocki@...el.com>,
        Viresh Kumar <viresh.kumar@...aro.org>,
        Vincent Guittot <vincent.guittot@...aro.org>,
        Paul Turner <pjt@...gle.com>,
        Quentin Perret <quentin.perret@....com>,
        Dietmar Eggemann <dietmar.eggemann@....com>,
        Morten Rasmussen <morten.rasmussen@....com>,
        Juri Lelli <juri.lelli@...hat.com>,
        Todd Kjos <tkjos@...gle.com>,
        Joel Fernandes <joelaf@...gle.com>,
        Steve Muckle <smuckle@...gle.com>
Subject: Re: [PATCH v4 08/16] sched/core: uclamp: propagate parent clamps

On Wed, Sep 12, 2018 at 5:51 AM, Patrick Bellasi
<patrick.bellasi@....com> wrote:
> On 08-Sep 20:02, Suren Baghdasaryan wrote:
>> On Tue, Aug 28, 2018 at 6:53 AM, Patrick Bellasi
>> <patrick.bellasi@....com> wrote:
>
> [...]
>
>> > +  cpu.util.min.effective
>> > +        A read-only single value file which exists on non-root cgroups and
>> > +        reports minimum utilization clamp value currently enforced on a task
>> > +        group.
>> > +
>> > +        The actual minimum utilization in the range [0, 1023].
>> > +
>> > +        This value can be lower then cpu.util.min in case a parent cgroup
>> > +        is enforcing a more restrictive clamping on minimum utilization.
>>
>> IMHO if cpu.util.min=0 means "no restrictions" on UCLAMP_MIN then
>> calling parent's lower cpu.util.min value "more restrictive clamping"
>> is confusing. I would suggest to rephrase this to smth like "...in
>> case a parent cgroup requires lower cpu.util.min clamping."
>
> Right, it's slightly confusing... still I would like to call out that
> a parent group can enforce something on its children. What about:
>
>    "... a parent cgroup allows only smaller minimum utilization values."
>
> Is that less confusing ?

SGTM.

>
> Otherwise I think your proposal could work too.
>
> [...]
>
>> >  #ifdef CONFIG_UCLAMP_TASK_GROUP
>> > +/**
>> > + * cpu_util_update_hier: propagete effective clamp down the hierarchy
>>
>> typo: propagate
>
> +1
>
> [...]
>
>> > +                * Skip the whole subtrees if the current effective clamp is
>> > +                * alredy matching the TG's clamp value.
>>
>> typo: already
>
> +1
>
>
> Cheers,
> Patrick
>
> --
> #include <best/regards.h>
>
> Patrick Bellasi