Re: [RFC v3 6/6] arm64/amu: use capacity_ref_freq to set AMU ratio

[Vincent Guittot]

On Mon, 23 Oct 2023 at 22:58, Ionela Voinescu <ionela.voinescu@xxxxxxx> wrote:
>
> Hi,
>
> On Wednesday 18 Oct 2023 at 18:25:40 (+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.
> >
> > The default value of the ratio ensures that arch_scale_freq_capacity()
> > returns max capacity until it is set to its correct value with the
> > cpu capacity and capacity_ref_freq.
> >
> > Signed-off-by: Vincent Guittot <vincent.guittot@xxxxxxxxxx>
> > ---
> >  arch/arm64/kernel/topology.c  | 18 ++++++++++--------
> >  drivers/base/arch_topology.c  | 14 ++++++++++++--
> >  include/linux/arch_topology.h |  1 +
> >  3 files changed, 23 insertions(+), 10 deletions(-)
> >
> > diff --git a/arch/arm64/kernel/topology.c b/arch/arm64/kernel/topology.c
> > index 817d788cd866..0f8f6e90c46d 100644
> > --- a/arch/arm64/kernel/topology.c
> > +++ b/arch/arm64/kernel/topology.c
> > @@ -82,7 +82,12 @@ int __init parse_acpi_topology(void)
> >  #undef pr_fmt
> >  #define pr_fmt(fmt) "AMU: " fmt
> >
> > -static DEFINE_PER_CPU_READ_MOSTLY(unsigned long, arch_max_freq_scale);
> > +/*
> > + * Ensure that amu_scale_freq_tick() will return SCHED_CAPACITY_SHIFT until
> > + * the CPU capacity and its assosciated frequency have been correctly
> > + * initialized.
>
> s/SCHED_CAPACITY_SHIFT/SCHED_CAPACITY_SCALE
>
> > + */
> > +static DEFINE_PER_CPU_READ_MOSTLY(unsigned long, arch_max_freq_scale) = (2 * SCHED_CAPACITY_SHIFT);
>
> It should be 1UL << (2 * SCHED_CAPACITY_SHIFT).

yes

>
> >  static DEFINE_PER_CPU(u64, arch_const_cycles_prev);
> >  static DEFINE_PER_CPU(u64, arch_core_cycles_prev);
> >  static cpumask_var_t amu_fie_cpus;
> > @@ -112,9 +117,9 @@ static inline bool freq_counters_valid(int cpu)
> >       return true;
> >  }
> >
> > -static int freq_inv_set_max_ratio(int cpu, u64 max_rate, u64 ref_rate)
> > +int freq_inv_set_max_ratio(int cpu, u64 max_rate)
> >  {
> > -     u64 ratio;
> > +     u64 ratio, ref_rate = arch_timer_get_rate();
> >
> >       if (unlikely(!max_rate || !ref_rate)) {
> >               pr_debug("CPU%d: invalid maximum or reference frequency.\n",
> > @@ -142,7 +147,7 @@ static int freq_inv_set_max_ratio(int cpu, u64 max_rate, u64 ref_rate)
> >               return -EINVAL;
> >       }
>
> The return value is no longer used so it might be worth declaring it to
> return void and WARN_ONCE for unlikely(!max_rate || !ref_rate).
>
> >
> > -     per_cpu(arch_max_freq_scale, cpu) = (unsigned long)ratio;
> > +     WRITE_ONCE(per_cpu(arch_max_freq_scale, cpu), (unsigned long)ratio);
> >
> >       return 0;
> >  }
> > @@ -195,10 +200,7 @@ static void amu_fie_setup(const struct cpumask *cpus)
> >               return;
> >
> >       for_each_cpu(cpu, cpus) {
> > -             if (!freq_counters_valid(cpu) ||
> > -                 freq_inv_set_max_ratio(cpu,
> > -                                        cpufreq_get_hw_max_freq(cpu) * 1000ULL,
> > -                                        arch_timer_get_rate()))
> > +             if (!freq_counters_valid(cpu))
> >                       return;
> >       }
> >
> > diff --git a/drivers/base/arch_topology.c b/drivers/base/arch_topology.c
> > index 2372ce791bb4..3a604b77b12d 100644
> > --- a/drivers/base/arch_topology.c
> > +++ b/drivers/base/arch_topology.c
> > @@ -344,6 +344,11 @@ bool __init topology_parse_cpu_capacity(struct device_node *cpu_node, int cpu)
> >       return !ret;
> >  }
> >
> > +int __weak freq_inv_set_max_ratio(int cpu, u64 max_rate)
> > +{
> > +     return 0;
> > +}
> > +
> >  #ifdef CONFIG_ACPI_CPPC_LIB
> >  #include <acpi/cppc_acpi.h>
> >
> > @@ -369,7 +374,6 @@ void topology_init_cpu_capacity_cppc(void)
> >                       capacity_scale = max_t(u64, capacity_scale, raw_capacity[cpu]);
> >
> >                       per_cpu(capacity_ref_freq, cpu) = cppc_perf_to_khz(&perf_caps, raw_capacity[cpu]);
> > -
> >                       pr_debug("cpu_capacity: CPU%d cpu_capacity=%u (raw).\n",
> >                                cpu, raw_capacity[cpu]);
> >                       continue;
> > @@ -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));
> > +
> >               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));
>
> capacity_ref_freq is in KHz while arch_timer_get_rate() is in Hz. One or
> the other needs to be scaled.
>
> The same in topology_init_cpu_capacity_cppc().
>
> Thanks,
> Ionela.
>
> > +     }
> >
> >       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..b6e95d763279 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);
> > +int freq_inv_set_max_ratio(int cpu, u64 max_rate);
> >  #endif
> >
> >  #endif /* _LINUX_ARCH_TOPOLOGY_H_ */
> > --
> > 2.34.1
> >