Re: [PATCH v4 1/5] arch_topology: Introduce thermal pressure update function

[Thara Gopinath <thara.gopinath@xxxxxxxxxx>]

On 11/9/21 2:57 PM, 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.
>
> Internally, the topology_update_thermal_pressure() operates on frequency
> in MHz and max CPU frequency is taken from 'freq_factor' (per-cpu).
>
> Signed-off-by: Lukasz Luba <lukasz.luba@xxxxxxx>

Reviewed-by: Thara Gopinath <thara.gopinath@xxxxxxxxxx>

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

> ---
>   arch/arm/include/asm/topology.h   |  1 +
>   arch/arm64/include/asm/topology.h |  1 +
>   drivers/base/arch_topology.c      | 43 ++++++++++++++++++++++++++++++-
>   include/linux/arch_topology.h     |  3 +++
>   include/linux/sched/topology.h    |  7 +++++
>   5 files changed, 54 insertions(+), 1 deletion(-)
>
> diff --git a/arch/arm/include/asm/topology.h b/arch/arm/include/asm/topology.h
> index 470299ee2fba..f1eafacc9a30 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_update_thermal_pressure	topology_update_thermal_pressure
>   
>   #else
>   
> diff --git a/arch/arm64/include/asm/topology.h b/arch/arm64/include/asm/topology.h
> index ec2db3419c41..7a421cbc99ed 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_update_thermal_pressure	topology_update_thermal_pressure
>   
>   #include <asm-generic/topology.h>
>   
> diff --git a/drivers/base/arch_topology.c b/drivers/base/arch_topology.c
> index fc0836f460fb..bed7d502c9a1 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 +169,47 @@ void topology_set_thermal_pressure(const struct cpumask *cpus,
>   }
>   EXPORT_SYMBOL_GPL(topology_set_thermal_pressure);
>   
> +/**
> + * topology_update_thermal_pressure() - Update thermal pressure for CPUs
> + * @cpus        : The related CPUs for which capacity has been reduced
> + * @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 reflects the currently allowed max CPUs frequency due to
> + * thermal capping. It might be also a boost frequency value, which is bigger
> + * than the internal 'freq_factor' max frequency. In such case the pressure
> + * value should simply be removed, since this is an indication that there is
> + * no thermal throttling. The @capped_freq must be provided in kHz.
> + */
> +void topology_update_thermal_pressure(const struct cpumask *cpus,
> +				      unsigned long capped_freq)
> +{
> +	unsigned long max_capacity, capacity;
> +	u32 max_freq;
> +	int cpu;
> +
> +	cpu = cpumask_first(cpus);
> +	max_capacity = arch_scale_cpu_capacity(cpu);
> +	max_freq = per_cpu(freq_factor, cpu);
> +
> +	/* Convert to MHz scale which is used in 'freq_factor' */
> +	capped_freq /= 1000;
> +
> +	/*
> +	 * 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);
> +
> +	arch_set_thermal_pressure(cpus, max_capacity - capacity);
> +}
> +EXPORT_SYMBOL_GPL(topology_update_thermal_pressure);
> +
>   static ssize_t cpu_capacity_show(struct device *dev,
>   				 struct device_attribute *attr,
>   				 char *buf)
> @@ -220,7 +262,6 @@ 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 b97cea83b25e..ace1e5dcf773 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_update_thermal_pressure(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 c07bfa2d80f2..6e89a8e43aa7 100644
> --- a/include/linux/sched/topology.h
> +++ b/include/linux/sched/topology.h
> @@ -273,6 +273,13 @@ void arch_set_thermal_pressure(const struct cpumask *cpus,
>   { }
>   #endif
>   
> +#ifndef arch_update_thermal_pressure
> +static __always_inline
> +void arch_update_thermal_pressure(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));