linux-kernel - Re: [PATCH v4 01/16] sched/core: uclamp: extend sched

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Message-ID: <20180905110108.GC20267@localhost.localdomain>
Date:   Wed, 5 Sep 2018 13:01:08 +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>,
        Quentin Perret <quentin.perret@....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>,
        Randy Dunlap <rdunlap@...radead.org>, linux-api@...r.kernel.org
Subject: Re: [PATCH v4 01/16] sched/core: uclamp: extend sched_setattr to
 support utilization clamping

Hi,

On 28/08/18 14:53, Patrick Bellasi wrote:

[...]

> Let's introduce a new API to set utilization clamping values for a
> specified task by extending sched_setattr, a syscall which already
> allows to define task specific properties for different scheduling
> classes.
> Specifically, a new pair of attributes allows to specify a minimum and
> maximum utilization which the scheduler should consider for a task.

AFAIK sched_setattr currently mandates that a policy is always specified
[1]. I was wondering if relaxing such requirement might be handy. Being
util clamp a cross-class feature it might be cumbersome to always have
to get current policy/params and use those with new umin/umax just to
change the latter.

sched_setparam already uses the in-kernel SETPARAM_POLICY thing, maybe
we could extend that to sched_setattr? Not sure exposing this to
userspace is a good idea though. :-/

Best,

- Juri

1 - https://elixir.bootlin.com/linux/v4.19-rc2/source/kernel/sched/core.c#L4564