linux-kernel - Re: [PATCH 3/6] sched: Allow sched_{get,set}attr to change latency

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Date:   Mon, 28 Mar 2022 14:41:27 +0200
From:   Vincent Guittot <vincent.guittot@...aro.org>
To:     Dietmar Eggemann <dietmar.eggemann@....com>
Cc:     mingo@...hat.com, peterz@...radead.org, juri.lelli@...hat.com,
        rostedt@...dmis.org, bsegall@...gle.com, mgorman@...e.de,
        linux-kernel@...r.kernel.org, parth@...ux.ibm.com,
        qais.yousef@....com, chris.hyser@...cle.com,
        pkondeti@...eaurora.org, Valentin.Schneider@....com,
        patrick.bellasi@...bug.net, David.Laight@...lab.com,
        pjt@...gle.com, pavel@....cz, tj@...nel.org,
        dhaval.giani@...cle.com, qperret@...gle.com,
        tim.c.chen@...ux.intel.com
Subject: Re: [PATCH 3/6] sched: Allow sched_{get,set}attr to change
 latency_nice of the task

On Mon, 28 Mar 2022 at 11:23, Dietmar Eggemann <dietmar.eggemann@....com> wrote:
>
> On 11/03/2022 17:14, Vincent Guittot wrote:
>
> [...]
>
> > @@ -98,6 +99,22 @@ struct sched_param {
> >   * scheduled on a CPU with no more capacity than the specified value.
> >   *
> >   * A task utilization boundary can be reset by setting the attribute to -1.
> > + *
> > + * Latency Tolerance Attributes
> > + * ===========================
> > + *
> > + * A subset of sched_attr attributes allows to specify the relative latency
> > + * requirements of a task with respect to the other tasks running/queued in the
> > + * system.
> > + *
> > + * @ sched_latency_nice      task's latency_nice value
> > + *
> > + * The latency_nice of a task can have any value in a range of
> > + * [LATENCY_NICE_MIN..LATENCY_NICE_MAX].
>
> s/LATENCY_NICE_MIN/MIN_LATENCY_NICE
> s/LATENCY_NICE_MAX/MAX_LATENCY_NICE

yes

>
> > + * A task with latency_nice with the value of LATENCY_NICE_MIN can be
> > + * taken for a task with lower latency requirements as opposed to the task with
> > + * higher latency_nice.
>
> low latency nice (priority): -20 -> high weight: 1024 ... Doesn't a task
> with MIN_LATENCY_NICE -20 have the highest latency requirements?

IIUC, What Parth wanted to say here is that low latency nice
(priority): -20  is taken for a task which needs low latency. The low
applies to latency not requirements

>
> [...]