linux-kernel - Re: [PATCH v4 7/7] arm64/amu: use capacity_ref

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Date:   Wed, 1 Nov 2023 10:04:27 +0100
From:   Vincent Guittot <vincent.guittot@...aro.org>
To:     Beata Michalska <beata.michalska@....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,
        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 v4 7/7] arm64/amu: use capacity_ref_freq to set AMU ratio

Hi Beata,

On Wed, 1 Nov 2023 at 00:59, Beata Michalska <beata.michalska@....com> wrote:
>
> On Fri, Oct 27, 2023 at 10:04:00AM +0200, Vincent Guittot wrote:
> > Use the new capacity_ref_freq to set the ratio that is used by AMU for
> > computing the arch_scale_freq_capacity().
> > This helps to keep everything aligned using the same reference for
> > computing CPUs capacity.
> >

[..]

> > @@ -381,6 +385,9 @@ void topology_init_cpu_capacity_cppc(void)
> >       }
> >
> >       for_each_possible_cpu(cpu) {
> > +             freq_inv_set_max_ratio(cpu,
> > +                                    per_cpu(capacity_ref_freq, cpu) * HZ_PER_KHZ);
> > +
> The capacity_ref_freq set earlier will still lead to units mismatch,
> as at the point of calling topology_init_cpu_capacity_cppc the lowest & nominal
> frequencies will be provided in MHz (unless I have missed smth).

I don't get your point:
the unit of per_cpu(capacity_freq_ref, cpu) is Khz

For cppc, we have
per_cpu(capacity_freq_ref, cpu) = cppc_perf_to_khz(&perf_caps,
raw_capacity[cpu]);

freq_inv_set_max_ratio() uses
arch_timer_get_rate() which returns a freq in Hz
and
per_cpu(capacity_freq_ref, cpu) * HZ_PER_KHZ. to get a freq in Hz too.

> This means that use of both, the capacity_ref_freq and the arch_freq_scale
> will generate unexpected results, so I guess this should get amended in the
> preceding patch (?) [1]
>
> ---
> BR
> B.
>
> [1] https://lore.kernel.org/linux-arm-kernel/20231027080400.56703-4-vincent.guittot@linaro.org/T/#m42daa167097edc190b1cfc05382c385ed801d909
>
> >               capacity = raw_capacity[cpu];
> >               capacity = div64_u64(capacity << SCHED_CAPACITY_SHIFT,
> >                                    capacity_scale);
> > @@ -422,8 +429,11 @@ init_cpu_capacity_callback(struct notifier_block *nb,
> >
> >       cpumask_andnot(cpus_to_visit, cpus_to_visit, policy->related_cpus);
> >
> > -     for_each_cpu(cpu, policy->related_cpus)
> > +     for_each_cpu(cpu, policy->related_cpus) {
> >               per_cpu(capacity_ref_freq, cpu) = policy->cpuinfo.max_freq;
> > +             freq_inv_set_max_ratio(cpu,
> > +                                    per_cpu(capacity_ref_freq, cpu) * HZ_PER_KHZ);
> > +     }
> >
> >       if (cpumask_empty(cpus_to_visit)) {
> >               topology_normalize_cpu_scale();
> > diff --git a/include/linux/arch_topology.h b/include/linux/arch_topology.h
> > index 38ca6c76af56..ffdf0b7c55fa 100644
> > --- a/include/linux/arch_topology.h
> > +++ b/include/linux/arch_topology.h
> > @@ -99,6 +99,7 @@ void update_siblings_masks(unsigned int cpu);
> >  void remove_cpu_topology(unsigned int cpuid);
> >  void reset_cpu_topology(void);
> >  int parse_acpi_topology(void);
> > +void freq_inv_set_max_ratio(int cpu, u64 max_rate);
> >  #endif
> >
> >  #endif /* _LINUX_ARCH_TOPOLOGY_H_ */
> > --
> > 2.34.1
> >