linux-kernel - Re: [PATCH v3 3/6] cpufreq/schedutil: use a fixed reference frequency

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Message-ID: <CAKfTPtDqFy-1dXH51JJ28XdH452K4ACrC3gr-v212s5-hH9RBw@mail.gmail.com>
Date:   Wed, 25 Oct 2023 14:51:47 +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,
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Subject: Re: [PATCH v3 3/6] cpufreq/schedutil: use a fixed reference frequency

On Wed, 25 Oct 2023 at 13:53, Peter Zijlstra <peterz@...radead.org> wrote:
>
> On Wed, Oct 18, 2023 at 06:25:37PM +0200, Vincent Guittot wrote:
>
> > +static __always_inline
> > +unsigned long get_capacity_ref_freq(struct cpufreq_policy *policy)
> > +{
> > +     unsigned int freq = arch_scale_freq_ref(policy->cpu);
> > +
> > +     if (freq)
> > +             return freq;
> > +
> > +     if (arch_scale_freq_invariant())
> > +             return policy->cpuinfo.max_freq;
> > +
> > +     return policy->cur;
> > +}
>
> Hmm, what should x86 do here? I know it mostly doesn't use these things,
> but would it make sense to stick the base frequency in ?

get_capacity_ref_freq() should return the frequency that is used as
the reference for the max compute capacity.

On Arm64, we have seen some inconsistency especially because we use
the energy model, we compute the CPU's capacity at boot and we can
have different compute capacity in our system whereas x86 always uses
SCHED_CAPACITY_SCALE even on hybrid system if I'm not wrong

So I was not sure that this will make any difference for x86 platform

>
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