linux-kernel - Re: [PATCH v10 10/15] sched: Introduce a sysctl for Energy Aware Scheduling

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Date:   Thu, 13 Dec 2018 15:03:58 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     Quentin Perret <quentin.perret@....com>
Cc:     Ingo Molnar <mingo@...nel.org>, rjw@...ysocki.net,
        linux-kernel@...r.kernel.org, linux-pm@...r.kernel.org,
        gregkh@...uxfoundation.org, mingo@...hat.com,
        dietmar.eggemann@....com, morten.rasmussen@....com,
        chris.redpath@....com, patrick.bellasi@....com,
        valentin.schneider@....com, vincent.guittot@...aro.org,
        thara.gopinath@...aro.org, viresh.kumar@...aro.org,
        tkjos@...gle.com, joel@...lfernandes.org, smuckle@...gle.com,
        adharmap@...eaurora.org, skannan@...eaurora.org,
        pkondeti@...eaurora.org, juri.lelli@...hat.com,
        edubezval@...il.com, srinivas.pandruvada@...ux.intel.com,
        currojerez@...eup.net, javi.merino@...nel.org
Subject: Re: [PATCH v10 10/15] sched: Introduce a sysctl for Energy Aware
 Scheduling

On Tue, Dec 11, 2018 at 02:49:01PM +0000, Quentin Perret wrote:
> Hi Ingo,
> 
> On Tuesday 11 Dec 2018 at 15:15:09 (+0100), Ingo Molnar wrote:
> > 
> > * Quentin Perret <quentin.perret@....com> wrote:
> > 
> > > In its current state, Energy Aware Scheduling (EAS) starts automatically
> > > on asymmetric platforms having an Energy Model (EM). However, there are
> > > users who want to have an EM (for thermal management for example), but
> > > don't want EAS with it.
> > 
> > Well, then introduce a new Kconfig variant for EAS, if it's super 
> > important to allow this to be disabled.
> > 
> > Why do we want to disable it - is it not reliable in some circumstances?
> 
> There are people out there using big.little systems who do not care
> about energy. Not very many of them, that is true, but they exist. And
> those people can be interested in having an Energy Model for
> IPA/thermal but also want to spread tasks to minimize latency for
> example. So those guys will appreciate a knob, I think. Otherwise EAS
> gets enabled/disabled only by side effects (by enabling/disabling
> schedutil for example).

Right, also we have a sysctl for numa-balancing, I figured having one
for eas would not be weird.