Re: [PATCH 1/5] arch_topology: Introduce thermal pressure update function

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

On 10/7/21 4:07 AM, Lukasz Luba wrote:
> The thermal pressure is a mechanism which is used for providing
> information about reduced CPU performance to the scheduler. Usually code
> has to convert the value from frequency units into capacity units,
> which are understandable by the scheduler. Create a common conversion code
> which can be just used via a handy API.
> 
> Signed-off-by: Lukasz Luba <lukasz.luba@arm.com>
> ---
>   arch/arm/include/asm/topology.h   |  1 +
>   arch/arm64/include/asm/topology.h |  1 +
>   drivers/base/arch_topology.c      | 36 ++++++++++++++++++++++++++++++-
>   include/linux/arch_topology.h     |  3 +++
>   include/linux/sched/topology.h    |  7 ++++++
>   5 files changed, 47 insertions(+), 1 deletion(-)
> 
> diff --git a/arch/arm/include/asm/topology.h b/arch/arm/include/asm/topology.h
> index 470299ee2fba..aee6c456c085 100644
> --- a/arch/arm/include/asm/topology.h
> +++ b/arch/arm/include/asm/topology.h
> @@ -24,6 +24,7 @@
>   /* Replace task scheduler's default thermal pressure API */
>   #define arch_scale_thermal_pressure topology_get_thermal_pressure
>   #define arch_set_thermal_pressure   topology_set_thermal_pressure
> +#define arch_thermal_pressure_update	topology_thermal_pressure_update
>   
>   #else
>   
> diff --git a/arch/arm64/include/asm/topology.h b/arch/arm64/include/asm/topology.h
> index ec2db3419c41..c997015402bc 100644
> --- a/arch/arm64/include/asm/topology.h
> +++ b/arch/arm64/include/asm/topology.h
> @@ -33,6 +33,7 @@ void update_freq_counters_refs(void);
>   /* Replace task scheduler's default thermal pressure API */
>   #define arch_scale_thermal_pressure topology_get_thermal_pressure
>   #define arch_set_thermal_pressure   topology_set_thermal_pressure
> +#define arch_thermal_pressure_update	topology_thermal_pressure_update
>   
>   #include <asm-generic/topology.h>
>   
> diff --git a/drivers/base/arch_topology.c b/drivers/base/arch_topology.c
> index 43407665918f..ad31513d0104 100644
> --- a/drivers/base/arch_topology.c
> +++ b/drivers/base/arch_topology.c
> @@ -25,6 +25,7 @@
>   static DEFINE_PER_CPU(struct scale_freq_data __rcu *, sft_data);
>   static struct cpumask scale_freq_counters_mask;
>   static bool scale_freq_invariant;
> +static DEFINE_PER_CPU(u32, freq_factor) = 1;
>   
>   static bool supports_scale_freq_counters(const struct cpumask *cpus)
>   {
> @@ -168,6 +169,40 @@ void topology_set_thermal_pressure(const struct cpumask *cpus,
>   }
>   EXPORT_SYMBOL_GPL(topology_set_thermal_pressure);
>   
> +/**
> + * topology_thermal_pressure_update() - Update thermal pressure for CPUs
> + * @cpus	: The related CPUs which capacity has been reduced

The related CPUs "for" which

> + * @capped_freq	: The maximum allowed frequency that CPUs can run at
> + *
> + * Update the value of thermal 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 must be less or equal to the max possible frequency and
> + * reflects the currently allowed max CPUs frequency due to thermal capping.
> + * The @capped_freq must be provided in kHz.
> + */
> +void topology_thermal_pressure_update(const struct cpumask *cpus,
> +				      unsigned long capped_freq)
> +{
> +	unsigned long max_capacity, capacity;
> +	int cpu;
> +
> +	if (!cpus)
> +		return;
> +
> +	cpu = cpumask_first(cpus);
> +	max_capacity = arch_scale_cpu_capacity(cpu);
> +
> +	/* Convert to MHz scale which is used in 'freq_factor' */
> +	capped_freq /= 1000;
> +
> +	capacity = capped_freq * max_capacity;
> +	capacity /= per_cpu(freq_factor, cpu);

use mult_frac as used in other implementations ?

-- 
Warm Regards
Thara (She/Her/Hers)

> +
> +	arch_set_thermal_pressure(cpus, max_capacity - capacity);
> +}
> +EXPORT_SYMBOL_GPL(topology_thermal_pressure_update);
> +
>   static ssize_t cpu_capacity_show(struct device *dev,
>   				 struct device_attribute *attr,
>   				 char *buf)
> @@ -220,7 +255,6 @@ static void update_topology_flags_workfn(struct work_struct *work)
>   	update_topology = 0;
>   }
>   
> -static DEFINE_PER_CPU(u32, freq_factor) = 1;
>   static u32 *raw_capacity;
>   
>   static int free_raw_capacity(void)
> diff --git a/include/linux/arch_topology.h b/include/linux/arch_topology.h
> index f180240dc95f..9e183621a59b 100644
> --- a/include/linux/arch_topology.h
> +++ b/include/linux/arch_topology.h
> @@ -59,6 +59,9 @@ static inline unsigned long topology_get_thermal_pressure(int cpu)
>   void topology_set_thermal_pressure(const struct cpumask *cpus,
>   				   unsigned long th_pressure);
>   
> +void topology_thermal_pressure_update(const struct cpumask *cpus,
> +				      unsigned long capped_freq);
> +
>   struct cpu_topology {
>   	int thread_id;
>   	int core_id;
> diff --git a/include/linux/sched/topology.h b/include/linux/sched/topology.h
> index 8f0f778b7c91..990d14814427 100644
> --- a/include/linux/sched/topology.h
> +++ b/include/linux/sched/topology.h
> @@ -266,6 +266,13 @@ void arch_set_thermal_pressure(const struct cpumask *cpus,
>   { }
>   #endif
>   
> +#ifndef arch_thermal_pressure_update
> +static __always_inline
> +void arch_thermal_pressure_update(const struct cpumask *cpus,
> +				      unsigned long capped_frequency)
> +{ }
> +#endif
> +
>   static inline int task_node(const struct task_struct *p)
>   {
>   	return cpu_to_node(task_cpu(p));
>