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Date:   Wed, 25 Oct 2023 13:54:56 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Vincent Guittot <vincent.guittot@...aro.org>
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,
        juri.lelli@...hat.com, dietmar.eggemann@....com,
        rostedt@...dmis.org, bsegall@...gle.com, mgorman@...e.de,
        bristot@...hat.com, vschneid@...hat.com, viresh.kumar@...aro.org,
        lenb@...nel.org, robert.moore@...el.com, lukasz.luba@....com,
        ionela.voinescu@....com, pierre.gondois@....com,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        linux-riscv@...ts.infradead.org, linux-pm@...r.kernel.org,
        linux-acpi@...r.kernel.org, acpica-devel@...ts.linuxfoundation.org,
        conor.dooley@...rochip.com, suagrfillet@...il.com,
        ajones@...tanamicro.com, lftan@...nel.org
Subject: Re: [PATCH v3 4/6] energy_model: use a fixed reference frequency

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?

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