linux-kernel - Re: [PATCH v2 10/12] sched/core: uclamp: use TG's clamps to restrict Task's clamps

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Date:   Thu, 26 Jul 2018 15:11:39 -0700
From:   Suren Baghdasaryan <surenb@...gle.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>,
        Juri Lelli <juri.lelli@...hat.com>,
        Todd Kjos <tkjos@...gle.com>,
        Joel Fernandes <joelaf@...gle.com>,
        Steve Muckle <smuckle@...gle.com>
Subject: Re: [PATCH v2 10/12] sched/core: uclamp: use TG's clamps to restrict
 Task's clamps

Sorry for the delay. Overlooked this comment...

On Tue, Jul 24, 2018 at 8:49 AM, Patrick Bellasi <patrick.bellasi@....com>
wrote:

> On 24-Jul 08:28, Suren Baghdasaryan wrote:
> > Hi Patrick. Thanks for the explanation and links. No more questions
> > from me on this one :)
>
> No problems at all!
>
> The important question is instead: does it makes sense for you too?
>

Well, it still feels unnatural to me due to the definition of the boost (at
least this much CPU bandwidth but higher should be fine).
Say I have a task which normally has specific boost and clamp requirements
(say TG.UCLAMP_MIN=20, TG.UCLAMP_MAX=80) which I want to temporarily boost
using a syscall to UCLAMP_MIN=60 (let's say a process should handle some
request and temporarily needs more CPU bandwidth). With this interface we
can clamp more than TG.UCLAMP_MAX value but we can't boost more than
TG.UCLAMP_MIN. For this usecase I would have to set TG.UCLAMP_MIN=80, then
use syscall to set SYSCALL.UCLAMP_MIN=20 to get effective UCLAMP_MIN=20 and
then set SYSCALL.UCLAMP_MIN=60 when I need that temporary boost.
To summarize, while this API does not stop me from achieving the desired
result it requires some hoop-jumping :)

>
> I think the important bits are that we are all on the same page about
> the end goals and features we like to have as well as the interface we use.
> This last has to fits best our goals and features while still being
> perfectly aligned with the frameworks we are integrating into... and
> that's still under discussion with Tejun on PATCH 08/12.
>
> Thanks again for your review!
>
> Cheers Patrick
>
> --
> #include <best/regards.h>
>
> Patrick Bellasi
>

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