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

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Message-ID: <20231213071722.u6n2fokrfs7hf3nb@vireshk-i7>
Date:   Wed, 13 Dec 2023 12:47:22 +0530
From:   Viresh Kumar <viresh.kumar@...aro.org>
To:     Vincent Guittot <vincent.guittot@...aro.org>
Cc:     catalin.marinas@....com, will@...nel.org, sudeep.holla@....com,
        rafael@...nel.org, agross@...nel.org, andersson@...nel.org,
        konrad.dybcio@...aro.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, lukasz.luba@....com,
        rui.zhang@...el.com, mhiramat@...nel.org,
        daniel.lezcano@...aro.org, amit.kachhap@...il.com,
        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 1/4] cpufreq: Add a cpufreq pressure feedback for the
 scheduler

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@...aro.org>
> ---
>  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 ?

> +				      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.

> +	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