linux-kernel - Re: [PATCH v3 01/14] sched/core: uclamp: extend sched

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Message-ID: <20180807095905.GB2288@localhost.localdomain>
Date:   Tue, 7 Aug 2018 11:59:05 +0200
From:   Juri Lelli <juri.lelli@...hat.com>
To:     Patrick Bellasi <patrick.bellasi@....com>
Cc:     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>,
        Dietmar Eggemann <dietmar.eggemann@....com>,
        Morten Rasmussen <morten.rasmussen@....com>,
        Todd Kjos <tkjos@...gle.com>,
        Joel Fernandes <joelaf@...gle.com>,
        Steve Muckle <smuckle@...gle.com>,
        Suren Baghdasaryan <surenb@...gle.com>
Subject: Re: [PATCH v3 01/14] sched/core: uclamp: extend sched_setattr to
 support utilization clamping

Hi,

Minor comments below.

On 06/08/18 17:39, Patrick Bellasi wrote:

[...]

> + *
> + * Task Utilization Attributes
> + * ===========================
> + *
> + * A subset of sched_attr attributes allows to specify the utilization which
> + * should be expected by a task. These attributes allows to inform the
                                                       ^
						     allow

> + * scheduler about the utilization boundaries within which is safe to schedule

Isn't all this more about providing hints than safety?

> + * the task. These utilization boundaries are valuable information to support
> + * scheduler decisions on both task placement and frequencies selection.
> + *
> + *  @sched_util_min	represents the minimum utilization
> + *  @sched_util_max	represents the maximum utilization
> + *
> + * Utilization is a value in the range [0..SCHED_CAPACITY_SCALE] which
> + * represents the percentage of CPU time used by a task when running at the
> + * maximum frequency on the highest capacity CPU of the system. Thus, for
> + * example, a 20% utilization task is a task running for 2ms every 10ms.
> + *
> + * A task with a min utilization value bigger then 0 is more likely to be
> + * scheduled on a CPU which can provide that bandwidth.
> + * A task with a max utilization value smaller then 1024 is more likely to be
> + * scheduled on a CPU which do not provide more then the required bandwidth.

Isn't s/bandwidth/capacity/ here, above, and in general where you use
the term "bandwidth" more appropriate? I wonder if overloading this term
(w.r.t. how is used with DEADLINE) might create confusion. In this case
we are not providing any sort of guarantees, it's a hint.

Best,

- Juri