Re: [Patch v4 5/6] thermal/cpu-cooling: Update thermal pressure in case of a maximum frequency capping

[Thara Gopinath <thara.gopinath@linaro.org>]

On 10/31/2019 12:29 PM, Dietmar Eggemann wrote:
> On 22.10.19 22:34, Thara Gopinath wrote:
>> Thermal governors can request for a cpu's maximum supported frequency
>> to be capped in case of an overheat event. This in turn means that the
>> maximum capacity available for tasks to run on the particular cpu is
>> reduced. Delta between the original maximum capacity and capped
>> maximum capacity is known as thermal pressure. Enable cpufreq cooling
>> device to update the thermal pressure in event of a capped
>> maximum frequency.
>>
>> Signed-off-by: Thara Gopinath <thara.gopinath@linaro.org>
>> ---
>>  drivers/thermal/cpu_cooling.c | 31 +++++++++++++++++++++++++++++--
>>  1 file changed, 29 insertions(+), 2 deletions(-)
>>
>> diff --git a/drivers/thermal/cpu_cooling.c b/drivers/thermal/cpu_cooling.c
>> index 391f397..2e6a979 100644
>> --- a/drivers/thermal/cpu_cooling.c
>> +++ b/drivers/thermal/cpu_cooling.c
>> @@ -218,6 +218,23 @@ static u32 cpu_power_to_freq(struct cpufreq_cooling_device *cpufreq_cdev,
>>  }
>>  
>>  /**
>> + * update_sched_max_capacity - update scheduler about change in cpu
>> + *					max frequency.
>> + * @policy - cpufreq policy whose max frequency is capped.
>> + */
>> +static void update_sched_max_capacity(struct cpumask *cpus,
>> +				      unsigned int cur_max_freq,
>> +				      unsigned int max_freq)
>> +{
>> +	int cpu;
>> +	unsigned long capacity = (cur_max_freq << SCHED_CAPACITY_SHIFT) /
>> +				  max_freq;
>> +
>> +	for_each_cpu(cpu, cpus)
>> +		update_thermal_pressure(cpu, capacity);
>> +}
>> +
>> +/**
>>   * get_load() - get load for a cpu since last updated
>>   * @cpufreq_cdev:	&struct cpufreq_cooling_device for this cpu
>>   * @cpu:	cpu number
>> @@ -320,6 +337,7 @@ static int cpufreq_set_cur_state(struct thermal_cooling_device *cdev,
>>  				 unsigned long state)
>>  {
>>  	struct cpufreq_cooling_device *cpufreq_cdev = cdev->devdata;
>> +	int ret;
>>  
>>  	/* Request state should be less than max_level */
>>  	if (WARN_ON(state > cpufreq_cdev->max_level))
>> @@ -331,8 +349,17 @@ static int cpufreq_set_cur_state(struct thermal_cooling_device *cdev,
>>  
>>  	cpufreq_cdev->cpufreq_state = state;
>>  
>> -	return dev_pm_qos_update_request(&cpufreq_cdev->qos_req,
>> -				cpufreq_cdev->freq_table[state].frequency);
>> +	ret = dev_pm_qos_update_request
>> +				(&cpufreq_cdev->qos_req,
>> +				 cpufreq_cdev->freq_table[state].frequency);
>> +
>> +	if (ret > 0)
>> +		update_sched_max_capacity
>> +				(cpufreq_cdev->policy->cpus,
>> +				 cpufreq_cdev->freq_table[state].frequency,
>> +				 cpufreq_cdev->policy->cpuinfo.max_freq);
>> +
>> +	return ret;
>>  }
>>  
>>  /**
>>
> 
> Why not getting rid of update_sched_max_capacity() entirely and call
> update_thermal_pressure() in cpu_cooling.c directly? Saves one level in
> the call chain and would mean less code for this feature.

Hi Dietmar,
Thanks for the review.

I did not want the scheduler piece of code to loop through the cpus.
Do you feel strongly about this one ?

Warm Regards
Thara
> 
> Just compile tested on arm64:
> 
> diff --git a/drivers/thermal/cpu_cooling.c b/drivers/thermal/cpu_cooling.c
> index 3211b4d3a899..bf36995013b0 100644
> --- a/drivers/thermal/cpu_cooling.c
> +++ b/drivers/thermal/cpu_cooling.c
> @@ -217,23 +217,6 @@ static u32 cpu_power_to_freq(struct
> cpufreq_cooling_device *cpufreq_cdev,
>         return freq_table[i - 1].frequency;
>  }
> 
> -/**
> - * update_sched_max_capacity - update scheduler about change in cpu
> - *                                     max frequency.
> - * @policy - cpufreq policy whose max frequency is capped.
> - */
> -static void update_sched_max_capacity(struct cpumask *cpus,
> -                                     unsigned int cur_max_freq,
> -                                     unsigned int max_freq)
> -{
> -       int cpu;
> -       unsigned long capacity = (cur_max_freq << SCHED_CAPACITY_SHIFT) /
> -                                 max_freq;
> -
> -       for_each_cpu(cpu, cpus)
> -               update_thermal_pressure(cpu, capacity);
> -}
> -
>  /**
>   * get_load() - get load for a cpu since last updated
>   * @cpufreq_cdev:      &struct cpufreq_cooling_device for this cpu
> @@ -353,7 +336,7 @@ static int cpufreq_set_cur_state(struct
> thermal_cooling_device *cdev,
>                                 cpufreq_cdev->freq_table[state].frequency);
> 
>         if (ret > 0)
> -               update_sched_max_capacity
> +               update_thermal_pressure
>                                 (cpufreq_cdev->policy->cpus,
>                                  cpufreq_cdev->freq_table[state].frequency,
>                                  cpufreq_cdev->policy->cpuinfo.max_freq);
> diff --git a/include/linux/sched.h b/include/linux/sched.h
> index 55dfe9634f67..5707813c7621 100644
> --- a/include/linux/sched.h
> +++ b/include/linux/sched.h
> @@ -1985,9 +1985,9 @@ static inline void rseq_syscall(struct pt_regs *regs)
>  #endif
> 
>  #ifdef CONFIG_SMP
> -void update_thermal_pressure(int cpu, u64 capacity);
> +void update_thermal_pressure(struct cpumask *cpus, unsigned int cur,
> unsigned int max);
>  #else
> -static inline void update_thermal_pressure(int cpu, u64 capacity)
> +static inline void update_thermal_pressure(struct cpumask *cpus,
> unsigned int cur, unsigned int max);
>  {
>  }
>  #endif
> diff --git a/kernel/sched/thermal.c b/kernel/sched/thermal.c
> index 0da31e12a5ff..691bdd79597a 100644
> --- a/kernel/sched/thermal.c
> +++ b/kernel/sched/thermal.c
> @@ -43,17 +43,16 @@ static DEFINE_PER_CPU(unsigned long, delta_capacity);
>   * the arch_scale_cpu_capacity and capped capacity is stored in per cpu
>   * delta_capacity.
>   */
> -void update_thermal_pressure(int cpu, u64 capped_freq_ratio)
> +void update_thermal_pressure(struct cpumask *cpus, unsigned int cur,
> unsigned int max)
>  {
> -       unsigned long __capacity, delta;
> +       int cpu;
> 
> -       /* Normalize the capped freq ratio */
> -       __capacity = (capped_freq_ratio * arch_scale_cpu_capacity(cpu)) >>
> -
> SCHED_CAPACITY_SHIFT;
> -       delta = arch_scale_cpu_capacity(cpu) -  __capacity;
> -       pr_debug("updating cpu%d thermal pressure to %lu\n", cpu, delta);
> +       for_each_cpu(cpu, cpus) {
> +               unsigned long scale_cap = arch_scale_cpu_capacity(cpu);
> +               unsigned long cur_cap = cur * scale_cap / max;
> 
> -       per_cpu(delta_capacity, cpu) = delta;
> +               per_cpu(delta_capacity, cpu) = scale_cap - cur_cap;
> +       }
>  }
> 


-- 
Warm Regards
Thara