linux-kernel - Re: [PATCH v3 4/6] energy_model: use a fixed reference frequency

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Message-ID: <CAKfTPtDhRcyHQKGy0aNLXLzGJ6LS+Of7ZjeQGGGv5f5qtNxiBg@mail.gmail.com>
Date:   Wed, 25 Oct 2023 14:54:27 +0200
From:   Vincent Guittot <vincent.guittot@...aro.org>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     linux@...linux.org.uk, catalin.marinas@....com, will@...nel.org,
        paul.walmsley@...ive.com, palmer@...belt.com,
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        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
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Subject: Re: [PATCH v3 4/6] energy_model: use a fixed reference frequency

On Wed, 25 Oct 2023 at 13:55, Peter Zijlstra <peterz@...radead.org> wrote:
>
> On Wed, Oct 18, 2023 at 06:25:38PM +0200, Vincent Guittot wrote:
> > The last item of a performance domain is not always the performance point
> > that has been used to compute CPU's capacity. This can lead to different
> > target frequency compared with other part of the system like schedutil and
> > would result in wrong energy estimation.
> >
> > A new arch_scale_freq_ref() is available to return a fixed and coherent
> > frequency reference that can be used when computing the CPU's frequency
> > for an level of utilization. Use this function to get this reference
> > frequency.
> >
> > Energy model is never used without defining arch_scale_freq_ref() but
> > can be compiled. Define a default arch_scale_freq_ref() returning 0
> > in such case.
> >
> > Signed-off-by: Vincent Guittot <vincent.guittot@...aro.org>
> > Reviewed-by: Lukasz Luba <lukasz.luba@....com>
> > Tested-by: Lukasz Luba <lukasz.luba@....com>
> >
> > ---
> >  include/linux/energy_model.h | 14 +++++++++++---
> >  1 file changed, 11 insertions(+), 3 deletions(-)
> >
> > diff --git a/include/linux/energy_model.h b/include/linux/energy_model.h
> > index b9caa01dfac4..1b0c8490d4bd 100644
> > --- a/include/linux/energy_model.h
> > +++ b/include/linux/energy_model.h
> > @@ -204,6 +204,14 @@ struct em_perf_state *em_pd_get_efficient_state(struct em_perf_domain *pd,
> >       return ps;
> >  }
> >
> > +#ifndef arch_scale_freq_ref
> > +static __always_inline
> > +unsigned int arch_scale_freq_ref(int cpu)
> > +{
> > +     return 0;
> > +}
> > +#endif
>
> Hmm, did I not see the exact same thing in cpufreq.h two patches ago?

Probably, this has been added because of error returned by some
allyes/randconfig on x86

>
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