linux-kernel - Re: [PATCH v7 02/14] sched/cpufreq: Prepare schedutil for Energy Aware Scheduling

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Date:   Thu, 27 Sep 2018 13:17:49 +0100
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 v7 02/14] sched/cpufreq: Prepare schedutil for Energy
 Aware Scheduling

Hi Rafael,

Very sorry for the late reply ...

On Tuesday 18 Sep 2018 at 23:33:22 (+0200), Rafael J. Wysocki wrote:
[...]
> The new "type" argument should be documented.
> 
> Also IMO using the special enum for it is quite confusing, because you
> ever only check one value from it directly.  What would be wrong with
> using a plain "bool" instead?

So, this part of the code was originally proposed by Peter. I basically
took it from the following message (hence the Suggested-by) which was
fine by me:

https://lore.kernel.org/lkml/20180709120138.GQ2494@hirez.programming.kicks-ass.net/

Also, one of the things that has been mentioned during reviews was that
other clients (such as cpuidle, IIRC) could potentially be interested
in a 'global' cpu util value. And since those clients might have
different needs than EAS or sugov, they might need a new entry in the
enum.

So that's probably the main argument for the enum, it is easy to extend.

[...]
> > +static unsigned long sugov_get_util(struct sugov_cpu *sg_cpu)
> > +{
> > +       struct rq *rq = cpu_rq(sg_cpu->cpu);
> > +       unsigned long util = cpu_util_cfs(rq);
> > +
> > +       sg_cpu->max = arch_scale_cpu_capacity(NULL, sg_cpu->cpu);
> > +       sg_cpu->bw_dl = cpu_bw_dl(rq);
> > +
> > +       return schedutil_freq_util(sg_cpu->cpu, util, FREQUENCY_UTIL);
> 
> If you add a "max" argument to schedutil_freq_util(), you can avoid
> the second (and arguably redundant) evaluation of
> arch_scale_cpu_capacity() in there.

OK

[...]
> > +enum schedutil_type {
> > +       FREQUENCY_UTIL,
> > +       ENERGY_UTIL,
> > +};
> 
> As I said above, I would just use "bool" instead of this new enum (it
> has two values too) or the new type needs to be documented.

As I said above, the enum has the good side of being easier to extend.
So, if we care about that, I guess I'd rather add a doc for the new
type.

> > +
> >  #ifdef CONFIG_CPU_FREQ_GOV_SCHEDUTIL
> > +unsigned long schedutil_freq_util(int cpu, unsigned long util_cfs,
> > +                                 enum schedutil_type type);
> > +
> >  static inline unsigned long cpu_bw_dl(struct rq *rq)
> >  {
> >         return (rq->dl.running_bw * SCHED_CAPACITY_SCALE) >> BW_SHIFT;
> > @@ -2199,6 +2207,12 @@ static inline unsigned long cpu_util_rt(struct rq *rq)
> >  {
> >         return READ_ONCE(rq->avg_rt.util_avg);
> >  }
> > +#else /* CONFIG_CPU_FREQ_GOV_SCHEDUTIL */
> > +static inline unsigned long schedutil_freq_util(int cpu, unsigned long util,
> > +                                 enum schedutil_type type)
> > +{
> > +       return util;
> > +}
> >  #endif
> 
> And I would add a wrapper around schedutil_freq_util(), called say
> schedutil_energy_util(), that would pass a specific value as the
> "type".

OK, that's fine by me.

Other than that, do you think these changes could be done later ? Or do
you see that as mandatory before the patches can be picked up ?

Thanks,
Quentin