linux-kernel - Re: [PATCH v12 6/8] sched/fair: Add sched group latency support

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Message-ID: <CAKfTPtAq-fRhgXw21RxLhT_ZZQUoMSZgGc90R_qoqkUhu+ADDw@mail.gmail.com>
Date:   Tue, 28 Feb 2023 10:09:47 +0100
From:   Vincent Guittot <vincent.guittot@...aro.org>
To:     Michal Koutný <mkoutny@...e.com>
Cc:     mingo@...hat.com, peterz@...radead.org, juri.lelli@...hat.com,
        dietmar.eggemann@....com, rostedt@...dmis.org, bsegall@...gle.com,
        mgorman@...e.de, bristot@...hat.com, vschneid@...hat.com,
        linux-kernel@...r.kernel.org, parth@...ux.ibm.com, tj@...nel.org,
        lizefan.x@...edance.com, hannes@...xchg.org,
        cgroups@...r.kernel.org, corbet@....net, linux-doc@...r.kernel.org,
        qyousef@...alina.io, chris.hyser@...cle.com,
        patrick.bellasi@...bug.net, David.Laight@...lab.com,
        pjt@...gle.com, pavel@....cz, qperret@...gle.com,
        tim.c.chen@...ux.intel.com, joshdon@...gle.com, timj@....org,
        kprateek.nayak@....com, yu.c.chen@...el.com,
        youssefesmat@...omium.org, joel@...lfernandes.org
Subject: Re: [PATCH v12 6/8] sched/fair: Add sched group latency support

On Mon, 27 Feb 2023 at 15:42, Michal Koutný <mkoutny@...e.com> wrote:
>
> On Mon, Feb 27, 2023 at 02:44:22PM +0100, Vincent Guittot <vincent.guittot@...aro.org> wrote:
> > Regarding the current use of latency nice to set a latency offset, the
> > problem doesn't appear because latency offset applies between entities
> > at the same level as you mentioned above
>
> Splendid, it turned out that way (latency nice analogous to bandwidth
> nice).
>
> > Does  my explanation above make sense to you ?
>
> Yes, thank you.
>
> Thus, I'd like to propose avoiding the use of "limit" in this context and
> stress the horizontal scope. For example:
>
> > +     This interface file allows reading and setting latency using the
> > +     same values used by sched_setattr(2). The latency_nice of a group is
> > +     used to limit the impact of the latency_nice of a task outside the
> > +     group.
>
> +     This interface file allows reading and setting latency using the
> +     same values used by sched_setattr(2). The latency_nice of a group is
> +     used to modify group members' latency with respect to sibling groups.

That sounds reasonable to me.

>
> Regards,
> Michal