linux-kernel - Re: [PATCH v7 05/14] sched: Introduce a sched

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Message-ID: <20181003162435.GA19252@hirez.programming.kicks-ass.net>
Date:   Wed, 3 Oct 2018 18:24:35 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Quentin Perret <quentin.perret@....com>
Cc:     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 v7 05/14] sched: Introduce a sched_feat for Energy Aware
 Scheduling

On Tue, Oct 02, 2018 at 02:08:21PM +0100, Quentin Perret wrote:
> On Tuesday 02 Oct 2018 at 14:34:16 (+0200), Peter Zijlstra wrote:

> > So these are debug knobs.. I would expect there to be a regular
> > static_key that is controlled by the presence of EM data.
> 
> Right, the issue I'm trying to solve with this is basically that _some_
> users will want to have an EM for the thermal stuff, but they will want
> EAS disabled. Some people (not very many that's true, but still) use
> big.little and don't care much about energy ...
> 
> So, there is a need for an EAS knob on the scheduler side. I don't mind
> it being something else than a sched_feat, but I couldn't see a better
> option. Another Kconfig (CONFIG_SCHED_ENERGY) ? A sysctl ?

Yeah, sysctl, see for example: sysctl.kernel.numa_balancing and the
sched_numa_balancing static_key that goes with it.

I would default enable EAS if the EM is there and valid, but allow
people to disable it.