linux-kernel - Re: [PATCH v10 02/15] sched/cpufreq: Prepare schedutil for Energy Aware Scheduling

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Date:   Tue, 11 Dec 2018 12:17:45 +0000
From:   Quentin Perret <quentin.perret@....com>
To:     "Rafael J. Wysocki" <rafael@...nel.org>
Cc:     Peter Zijlstra <peterz@...radead.org>,
        "Rafael J. Wysocki" <rjw@...ysocki.net>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Linux PM <linux-pm@...r.kernel.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Ingo Molnar <mingo@...hat.com>,
        Dietmar Eggemann <dietmar.eggemann@....com>,
        Morten Rasmussen <morten.rasmussen@....com>,
        Chris Redpath <chris.redpath@....com>,
        Patrick Bellasi <patrick.bellasi@....com>,
        Valentin Schneider <valentin.schneider@....com>,
        Vincent Guittot <vincent.guittot@...aro.org>,
        Thara Gopinath <thara.gopinath@...aro.org>,
        Viresh Kumar <viresh.kumar@...aro.org>,
        Todd Kjos <tkjos@...gle.com>,
        Joel Fernandes <joel@...lfernandes.org>,
        Steve Muckle <smuckle@...gle.com>, adharmap@...eaurora.org,
        Saravana Kannan <skannan@...eaurora.org>,
        Pavan Kondeti <pkondeti@...eaurora.org>,
        Juri Lelli <juri.lelli@...hat.com>,
        Eduardo Valentin <edubezval@...il.com>,
        Srinivas Pandruvada <srinivas.pandruvada@...ux.intel.com>,
        currojerez@...eup.net, Javi Merino <javi.merino@...nel.org>
Subject: Re: [PATCH v10 02/15] sched/cpufreq: Prepare schedutil for Energy
 Aware Scheduling

Hi Rafael,

On Tuesday 11 Dec 2018 at 13:01:24 (+0100), Rafael J. Wysocki wrote:
> On Mon, Dec 3, 2018 at 10:56 AM Quentin Perret <quentin.perret@....com> wrote:
> 
> [cut]
> 
> >  #ifdef CONFIG_CPU_FREQ_GOV_SCHEDUTIL
> > +/**
> > + * enum schedutil_type - CPU utilization type
> > + * @FREQUENCY_UTIL:    Utilization used to select frequency
> > + * @ENERGY_UTIL:       Utilization used during energy calculation
> > + *
> > + * The utilization signals of all scheduling classes (CFS/RT/DL) and IRQ time
> > + * need to be aggregated differently depending on the usage made of them. This
> > + * enum is used within schedutil_freq_util() to differentiate the types of
> > + * utilization expected by the callers, and adjust the aggregation accordingly.
> > + */
> > +enum schedutil_type {
> > +       FREQUENCY_UTIL,
> > +       ENERGY_UTIL,
> > +};
> 
> Why not to use bool instead of this?  Do you expect to have more than
> just two values in the future?  If so, what would be the third one?

Indeed, the only reason is that an enum is easier to extend, if need be.
I think you mentioned some time ago that CPUIdle could be, in principle,
interested in having access to aggregated utilization signals of CPUs:

https://lore.kernel.org/lkml/CAJZ5v0j=EYnANGAj9bd44eeux1eCfeMtdn9npe5pSAzE8EVKaA@mail.gmail.com/

So yeah, I kept Peter's original enum and went for documenting the type,
as you suggested on v7 :-)

Thanks,
Quentin