linux-kernel - Re: [PATCH v5 10/14] sched/cpufreq: Refactor the utilization aggregation method

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Message-ID: <20180802173601.GO2494@hirez.programming.kicks-ass.net>
Date:   Thu, 2 Aug 2018 19:36:01 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Quentin Perret <quentin.perret@....com>
Cc:     skannan@...eaurora.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@...cinc.com, skannan@...cinc.com, pkondeti@...eaurora.org,
        juri.lelli@...hat.com, edubezval@...il.com,
        srinivas.pandruvada@...ux.intel.com, currojerez@...eup.net,
        javi.merino@...nel.org, linux-pm-owner@...r.kernel.org
Subject: Re: [PATCH v5 10/14] sched/cpufreq: Refactor the utilization
 aggregation method

On Thu, Aug 02, 2018 at 04:21:11PM +0100, Quentin Perret wrote:
> On Thursday 02 Aug 2018 at 14:45:11 (+0200), Peter Zijlstra wrote:

> > To clarify, it makes absolutely no sense what so ever to attempt EAS
> > when the DVFS control is not coordinated.
> 
> I tend to agree with that, but at the same time even if we create a very
> strong dependency on schedutil, we will have no guarantee that the actual
> frequencies used on the platform are the ones we predicted in EAS.

Sure; on x86 for example our micro-code does whatever. But using
schedutil we at least 'guide' it in the general direction we'd expect
with the control that is available.

Using a !schedutil governor doesn't even get us that and we're basically
running on random input without any feedback to close the loop. Not
something I feel we should support or care for.