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

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Message-ID: <20180912125133.GE1413@e110439-lin>
Date:   Wed, 12 Sep 2018 13:51:33 +0100
From:   Patrick Bellasi <patrick.bellasi@....com>
To:     Suren Baghdasaryan <surenb@...gle.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 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 ?

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