Re: [PATCH v4 7/7] arm64/amu: use capacity_ref_freq to set AMU ratio

Vincent Guittot
2023-11-01T09:04:45Z

Hi Beata,

On Wed, 1 Nov 2023 at 00:59, Beata Michalska <beata.michalska@arm.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
> >