linux-kernel - Re: [PATCH v10 13/16] sched/core: uclamp: Propagate parent clamps

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Date:   Mon, 24 Jun 2019 10:46:07 -0700
From:   Tejun Heo <tj@...nel.org>
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>,
        "Rafael J . Wysocki" <rafael.j.wysocki@...el.com>,
        Vincent Guittot <vincent.guittot@...aro.org>,
        Viresh Kumar <viresh.kumar@...aro.org>,
        Paul Turner <pjt@...gle.com>,
        Quentin Perret <quentin.perret@....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>,
        Suren Baghdasaryan <surenb@...gle.com>,
        Alessio Balsini <balsini@...roid.com>
Subject: Re: [PATCH v10 13/16] sched/core: uclamp: Propagate parent clamps

Hello, Patrick.

On Mon, Jun 24, 2019 at 06:34:05PM +0100, Patrick Bellasi wrote:
> > On Fri, Jun 21, 2019 at 09:42:14AM +0100, Patrick Bellasi wrote:
> > > Since it can be interesting for userspace, e.g. system management
> > > software, to know exactly what the currently propagated/enforced
> > > configuration is, the effective clamp values are exposed to user-space
> > > by means of a new pair of read-only attributes
> > > cpu.util.{min,max}.effective.
> > 
> > Can we not add the effective interface file for now?
> 
> You mean just the (read-only) user-space API right?

Yeah.

> I found it quite convenient, even just for debugging.
> Moreover it allows a container to know what it's exactly getting...

I fully agree.

> > I don't think it's a bad idea but would like to think more about it.
> > For cpuset, it was needed because configuration was so interwoven
> > with the effective masks, but we don't generally do this for other
> > min/max or weight knobs, all of which have effective hierarchical
> > values and I'm not quite sure about adding .effective for all of
> > them.
> > It could be that that's what we end up doing eventually but
> > I'd like to think a bit more about it.
> 
> ... but I see your point and, since it's not strictly required, I
> think we can drop it in v11. Will check better if it's of any use
> apart from debugging/testing support.

Yeah, I just wanna figure out a plan which works for other controllers
too.  It could be that the right thing to do is just adding .effective
to everything but idk I need to think more about it.

Thanks.

-- 
tejun