Re: [PATCH v4 1/5] cpufreq: Add a cpufreq pressure feedback for the scheduler

[Qais Yousef]

On 01/09/24 17:46, 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 | 36 ++++++++++++++++++++++++++++++++++++
>  include/linux/cpufreq.h   | 10 ++++++++++
>  2 files changed, 46 insertions(+)
> 
> diff --git a/drivers/cpufreq/cpufreq.c b/drivers/cpufreq/cpufreq.c
> index 44db4f59c4cc..f4eee3d107f1 100644
> --- a/drivers/cpufreq/cpufreq.c
> +++ b/drivers/cpufreq/cpufreq.c
> @@ -2563,6 +2563,40 @@ 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);
> +	max_freq = arch_scale_freq_ref(cpu);
> +	capped_freq = policy->max;
> +
> +	/*
> +	 * Handle properly the boost frequencies, which should simply clean
> +	 * the cpufreq pressure value.
> +	 */
> +	if (max_freq <= capped_freq) {
> +		pressure = 0;
> +	} else {
> +		max_capacity = arch_scale_cpu_capacity(cpu);
> +		pressure = max_capacity -
> +			   mult_frac(max_capacity, capped_freq, max_freq);
> +	}
> +
> +	for_each_cpu(cpu, policy->related_cpus)
> +		WRITE_ONCE(per_cpu(cpufreq_pressure, cpu), pressure);

Is this WRITE_ONCE() required? I don't see why. But assuming I missed
something, better pair it with READ_ONCE() in cpufreq_get_pressure()?

Beside that, LGTM

Reviewed-by: Qais Yousef <qyousef@xxxxxxxxxxx>

> +}
> +
>  /**
>   * cpufreq_set_policy - Modify cpufreq policy parameters.
>   * @policy: Policy object to modify.
> @@ -2618,6 +2652,8 @@ 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
>