Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::3:1 as permitted sender) client-ip=2620:137:e000::3:1;
MIME-Version: 1.0
References: <20230901130312.247719-1-vincent.guittot@linaro.org>
 <20230901130312.247719-5-vincent.guittot@linaro.org> <8cfa9edb-67f9-80f9-0a5c-1920f95b338a@arm.com>
In-Reply-To: <8cfa9edb-67f9-80f9-0a5c-1920f95b338a@arm.com>
From:   Vincent Guittot <vincent.guittot@linaro.org>
Date:   Fri, 15 Sep 2023 15:35:46 +0200
Message-ID: <CAKfTPtDxJjj6wtpRnLjUi65j+5sQyYcHsQzbd+eSQCf4MVOiWA@mail.gmail.com>
Subject: Re: [PATCH 4/4] energy_model: use a fixed reference frequency
To:     Dietmar Eggemann <dietmar.eggemann@arm.com>
Cc:     linux@armlinux.org.uk, catalin.marinas@arm.com, will@kernel.org,
        paul.walmsley@sifive.com, palmer@dabbelt.com,
        aou@eecs.berkeley.edu, sudeep.holla@arm.com,
        gregkh@linuxfoundation.org, rafael@kernel.org, mingo@redhat.com,
        peterz@infradead.org, juri.lelli@redhat.com, rostedt@goodmis.org,
        bsegall@google.com, mgorman@suse.de, bristot@redhat.com,
        vschneid@redhat.com, viresh.kumar@linaro.org,
        linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org,
        linux-riscv@lists.infradead.org, linux-pm@vger.kernel.org,
        conor.dooley@microchip.com, suagrfillet@gmail.com,
        ajones@ventanamicro.com, lftan@kernel.org
Content-Type: text/plain; charset="UTF-8"
Precedence: bulk

On Thu, 14 Sept 2023 at 23:07, Dietmar Eggemann
<dietmar.eggemann@arm.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);
>
> [...]
>