linux-kernel - Re: [PATCH 4/4] energy_model: use a fixed reference frequency

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Message-ID: <CAKfTPtDxJjj6wtpRnLjUi65j+5sQyYcHsQzbd+eSQCf4MVOiWA@mail.gmail.com>
Date:   Fri, 15 Sep 2023 15:35:46 +0200
From:   Vincent Guittot <vincent.guittot@...aro.org>
To:     Dietmar Eggemann <dietmar.eggemann@....com>
Cc:     linux@...linux.org.uk, catalin.marinas@....com, will@...nel.org,
        paul.walmsley@...ive.com, palmer@...belt.com,
        aou@...s.berkeley.edu, sudeep.holla@....com,
        gregkh@...uxfoundation.org, rafael@...nel.org, mingo@...hat.com,
        peterz@...radead.org, juri.lelli@...hat.com, rostedt@...dmis.org,
        bsegall@...gle.com, mgorman@...e.de, bristot@...hat.com,
        vschneid@...hat.com, viresh.kumar@...aro.org,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        linux-riscv@...ts.infradead.org, linux-pm@...r.kernel.org,
        conor.dooley@...rochip.com, suagrfillet@...il.com,
        ajones@...tanamicro.com, lftan@...nel.org
Subject: Re: [PATCH 4/4] energy_model: use a fixed reference frequency

On Thu, 14 Sept 2023 at 23:07, Dietmar Eggemann
<dietmar.eggemann@....com> wrote:
>
> On 01/09/2023 15:03, Vincent Guittot wrote:
>
> [...]
>
> > diff --git a/include/linux/energy_model.h b/include/linux/energy_model.h
> > index b9caa01dfac4..7ee07be6928e 100644
> > --- a/include/linux/energy_model.h
> > +++ b/include/linux/energy_model.h
> > @@ -204,6 +204,20 @@ struct em_perf_state *em_pd_get_efficient_state(struct em_perf_domain *pd,
> >       return ps;
> >  }
> >
> > +#ifdef arch_scale_freq_ref
> > +static __always_inline
> > +unsigned long  arch_scale_freq_ref_em(int cpu, struct em_perf_domain *pd)
>
> Why is this function named with the arch prefix?
>
> So far we have 5 arch functions (arch_scale_freq_tick() <->
> arch_scale_freq_ref()) and e.g. Arm/Arm64 defines them with there
> topology_foo implementations.
>
> Isn't arch_scale_freq_ref_em() (as well as arch_scale_freq_ref_policy())
> different in this sense and so a proper EM function which should
> manifest in its name?

arch_scale_freq_ref_em() is there to handle cases where
arch_scale_freq_ref() is not defined by arch. I keep arch_ prefix
because this should be provided by architecture which wants to use EM.

In the case of EM, it's only there for allyes|randconfig on arch that
doesn't use arch_topology.c like x86_64

>
> > +{
> > +     return arch_scale_freq_ref(cpu);
> > +}
> > +#else
> > +static __always_inline
> > +unsigned long  arch_scale_freq_ref_em(int cpu, struct em_perf_domain *pd)
> > +{
> > +     return pd->table[pd->nr_perf_states - 1].frequency;
> > +}
> > +#endif
>
> [...]
>
> > @@ -241,11 +255,11 @@ static inline unsigned long em_cpu_energy(struct em_perf_domain *pd,
> >        */
> >       cpu = cpumask_first(to_cpumask(pd->cpus));
> >       scale_cpu = arch_scale_cpu_capacity(cpu);
> > -     ps = &pd->table[pd->nr_perf_states - 1];
> > +     ref_freq = arch_scale_freq_ref_em(cpu, pd);
>
> Why not using existing `unsigned long freq` here like in schedutil's
> get_next_freq()?

Find it easier to read and understand and will not make any difference
in the compiled code

>
> >
> >       max_util = map_util_perf(max_util);
>
> [...]
>