Re: [PATCH 1/4] cpufreq: Add a cpufreq pressure feedback for the scheduler

[Vincent Guittot]

On Wed, 13 Dec 2023 at 08:17, Viresh Kumar <viresh.kumar@xxxxxxxxxx> wrote:
>
> On 12-12-23, 15:27, Vincent Guittot wrote:
> > Provide to the scheduler a feedback about the temporary max available
> > capacity. Unlike arch_update_thermal_pressure, this doesn't need to be
> > filtered as the pressure will happen for dozens ms or more.
> >
> > Signed-off-by: Vincent Guittot <vincent.guittot@xxxxxxxxxx>
> > ---
> >  drivers/cpufreq/cpufreq.c | 48 +++++++++++++++++++++++++++++++++++++++
> >  include/linux/cpufreq.h   | 10 ++++++++
> >  2 files changed, 58 insertions(+)
> >
> > diff --git a/drivers/cpufreq/cpufreq.c b/drivers/cpufreq/cpufreq.c
> > index 44db4f59c4cc..7d5f71be8d29 100644
> > --- a/drivers/cpufreq/cpufreq.c
> > +++ b/drivers/cpufreq/cpufreq.c
> > @@ -2563,6 +2563,50 @@ int cpufreq_get_policy(struct cpufreq_policy *policy, unsigned int cpu)
> >  }
> >  EXPORT_SYMBOL(cpufreq_get_policy);
> >
> > +DEFINE_PER_CPU(unsigned long, cpufreq_pressure);
> > +EXPORT_PER_CPU_SYMBOL_GPL(cpufreq_pressure);
> > +
> > +/**
> > + * cpufreq_update_pressure() - Update cpufreq pressure for CPUs
> > + * @cpus        : The related CPUs for which max capacity has been reduced
> > + * @capped_freq : The maximum allowed frequency that CPUs can run at
> > + *
> > + * Update the value of cpufreq pressure for all @cpus in the mask. The
> > + * cpumask should include all (online+offline) affected CPUs, to avoid
> > + * operating on stale data when hot-plug is used for some CPUs. The
> > + * @capped_freq reflects the currently allowed max CPUs frequency due to
> > + * freq_qos capping. It might be also a boost frequency value, which is bigger
> > + * than the internal 'capacity_freq_ref' max frequency. In such case the
> > + * pressure value should simply be removed, since this is an indication that
> > + * there is no capping. The @capped_freq must be provided in kHz.
> > + */
> > +static void cpufreq_update_pressure(const struct cpumask *cpus,
>
> Since this is defined as 'static', why not just pass policy here ?

Mainly because we only need the cpumask and also because this follows
the same pattern as other place like arch_topology.c

>
> > +                                   unsigned long capped_freq)
> > +{
> > +     unsigned long max_capacity, capacity, pressure;
> > +     u32 max_freq;
> > +     int cpu;
> > +
> > +     cpu = cpumask_first(cpus);
> > +     max_capacity = arch_scale_cpu_capacity(cpu);
>
> This anyway expects all of them to be from the same policy ..
>
> > +     max_freq = arch_scale_freq_ref(cpu);
> > +
> > +     /*
> > +      * Handle properly the boost frequencies, which should simply clean
> > +      * the thermal pressure value.
> > +      */
> > +     if (max_freq <= capped_freq)
> > +             capacity = max_capacity;
> > +     else
> > +             capacity = mult_frac(max_capacity, capped_freq, max_freq);
> > +
> > +     pressure = max_capacity - capacity;
> > +
>
> Extra blank line here.
>
> > +
> > +     for_each_cpu(cpu, cpus)
> > +             WRITE_ONCE(per_cpu(cpufreq_pressure, cpu), pressure);
> > +}
> > +
> >  /**
> >   * cpufreq_set_policy - Modify cpufreq policy parameters.
> >   * @policy: Policy object to modify.
> > @@ -2584,6 +2628,7 @@ static int cpufreq_set_policy(struct cpufreq_policy *policy,
> >  {
> >       struct cpufreq_policy_data new_data;
> >       struct cpufreq_governor *old_gov;
> > +     struct cpumask *cpus;
> >       int ret;
> >
> >       memcpy(&new_data.cpuinfo, &policy->cpuinfo, sizeof(policy->cpuinfo));
> > @@ -2618,6 +2663,9 @@ static int cpufreq_set_policy(struct cpufreq_policy *policy,
> >       policy->max = __resolve_freq(policy, policy->max, CPUFREQ_RELATION_H);
> >       trace_cpu_frequency_limits(policy);
> >
> > +     cpus = policy->related_cpus;
>
> You don't need the extra variable anyway, but lets just pass policy
> instead to the routine.

In fact I have followed what was done in cpufreq_cooling.c with
arch_update_thermal_pressure().

Will remove it

>
> > +     cpufreq_update_pressure(cpus, policy->max);
> > +
> >       policy->cached_target_freq = UINT_MAX;
> >
> >       pr_debug("new min and max freqs are %u - %u kHz\n",
> > diff --git a/include/linux/cpufreq.h b/include/linux/cpufreq.h
> > index afda5f24d3dd..b1d97edd3253 100644
> > --- a/include/linux/cpufreq.h
> > +++ b/include/linux/cpufreq.h
> > @@ -241,6 +241,12 @@ struct kobject *get_governor_parent_kobj(struct cpufreq_policy *policy);
> >  void cpufreq_enable_fast_switch(struct cpufreq_policy *policy);
> >  void cpufreq_disable_fast_switch(struct cpufreq_policy *policy);
> >  bool has_target_index(void);
> > +
> > +DECLARE_PER_CPU(unsigned long, cpufreq_pressure);
> > +static inline unsigned long cpufreq_get_pressure(int cpu)
> > +{
> > +     return per_cpu(cpufreq_pressure, cpu);
> > +}
> >  #else
> >  static inline unsigned int cpufreq_get(unsigned int cpu)
> >  {
> > @@ -263,6 +269,10 @@ static inline bool cpufreq_supports_freq_invariance(void)
> >       return false;
> >  }
> >  static inline void disable_cpufreq(void) { }
> > +static inline unsigned long cpufreq_get_pressure(int cpu)
> > +{
> > +     return 0;
> > +}
> >  #endif
> >
> >  #ifdef CONFIG_CPU_FREQ_STAT
> > --
> > 2.34.1
>
> --
> viresh