linux-kernel - Re: [PATCH v2 1/5] cpufreq: Add a cpufreq pressure feedback for the scheduler

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Message-ID: <CAJZ5v0iChOQKpHaQy+Q0e9bBDjPsB107qk0FfT1z8_exFXiJdQ@mail.gmail.com>
Date: Thu, 21 Dec 2023 21:01:51 +0100
From: "Rafael J. Wysocki" <rafael@...nel.org>
To: Vincent Guittot <vincent.guittot@...aro.org>
Cc: catalin.marinas@....com, will@...nel.org, sudeep.holla@....com, 
	rafael@...nel.org, viresh.kumar@...aro.org, agross@...nel.org, 
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	rostedt@...dmis.org, bsegall@...gle.com, mgorman@...e.de, bristot@...hat.com, 
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	mhiramat@...nel.org, daniel.lezcano@...aro.org, amit.kachhap@...il.com, 
	linux@...linux.org.uk, corbet@....net, linux-arm-kernel@...ts.infradead.org, 
	linux-kernel@...r.kernel.org, linux-pm@...r.kernel.org, 
	linux-arm-msm@...r.kernel.org, linux-trace-kernel@...r.kernel.org
Subject: Re: [PATCH v2 1/5] cpufreq: Add a cpufreq pressure feedback for the scheduler

On Thu, Dec 21, 2023 at 8:57 PM Rafael J. Wysocki <rafael@...nel.org> wrote:
>
> On Thu, Dec 21, 2023 at 4:24 PM Vincent Guittot
> <vincent.guittot@...aro.org> 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@...aro.org>
> > ---
> >  drivers/cpufreq/cpufreq.c | 34 ++++++++++++++++++++++++++++++++++
> >  include/linux/cpufreq.h   | 10 ++++++++++
> >  2 files changed, 44 insertions(+)
> >
> > diff --git a/drivers/cpufreq/cpufreq.c b/drivers/cpufreq/cpufreq.c
> > index 44db4f59c4cc..15bd41f9bb5e 100644
> > --- a/drivers/cpufreq/cpufreq.c
> > +++ b/drivers/cpufreq/cpufreq.c
> > @@ -2563,6 +2563,38 @@ int cpufreq_get_policy(struct cpufreq_policy *policy, unsigned int cpu)
> >  }
> >  EXPORT_SYMBOL(cpufreq_get_policy);
> >
> > +DEFINE_PER_CPU(unsigned long, cpufreq_pressure);
> > +
> > +/**
> > + * cpufreq_update_pressure() - Update cpufreq pressure for CPUs
> > + * @policy: cpufreq policy of the CPUs.
> > + *
> > + * Update the value of cpufreq pressure for all @cpus in the policy.
> > + */
> > +static void cpufreq_update_pressure(struct cpufreq_policy *policy)
> > +{
> > +       unsigned long max_capacity, capped_freq, pressure;
> > +       u32 max_freq;
> > +       int cpu;
> > +
> > +       cpu = cpumask_first(policy->related_cpus);
> > +       pressure = max_capacity = arch_scale_cpu_capacity(cpu);
>
> I would prefer two separate statements instead of the above.
>
> Other than this
>
> Acked-by: Rafael J. Wysocki <rafael@...nel.org>
>
> > +       capped_freq = policy->max;
> > +       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)
> > +               pressure -= max_capacity;

Actually, it would be somewhat cleaner to do

pressure = 0;

here and

> > +       else
> > +               pressure -= mult_frac(max_capacity, capped_freq, max_freq);

pressure = max_capacity - mult_frac(max_capacity, capped_freq, max_freq);

and it would not be necessary to initialize pressure.

> > +
> > +       for_each_cpu(cpu, policy->related_cpus)
> > +               WRITE_ONCE(per_cpu(cpufreq_pressure, cpu), pressure);
> > +}
> > +
> >  /**
> >   * cpufreq_set_policy - Modify cpufreq policy parameters.
> >   * @policy: Policy object to modify.
> > @@ -2618,6 +2650,8 @@ static int cpufreq_set_policy(struct cpufreq_policy *policy,
> >         policy->max = __resolve_freq(policy, policy->max, CPUFREQ_RELATION_H);
> >         trace_cpu_frequency_limits(policy);
> >
> > +       cpufreq_update_pressure(policy);
> > +
> >         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
> >