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

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Date:   Thu, 2 Nov 2023 11:30:03 +0100
From:   Beata Michalska <beata.michalska@....com>
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,
        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 Vincent,

On Wed, Nov 01, 2023 at 10:04:27AM +0100, Vincent Guittot wrote:
> 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.
> 
Apologies, I should have been more verbose here.
Before the change made in [1] the cppc_perf_to_khz was indeed operating on
lowest & nominal frequency values expressed in kHZ, as those were appropriately
amended:
cppc_cpufreq_cpu_init
	|__> cppc_cpufreq_get_cpu_data:
		|__> 	...
			/* Convert the lowest and nominal freq from MHz to KHz */
			cpu_data->perf_caps.lowest_freq *= 1000;
			cpu_data->perf_caps.nominal_freq *= 1000;

So far cppc_perf_to_khz (previously cppc_cpufreq_perf_to_khz) was being called
with the post-processed CPC data (through cppc_cpufreq_get_cpu_data) and thus
guaranteed to be operating on values in kHz.
With the new changes the cppc_perf_to_khz will operate on raw CPC data,
which are expressed in MHz.(as per acpi spec)

---
Best Regards
B.
> > 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
> > >