Re: [RFC v3 6/6] arm64/amu: use capacity_ref_freq to set AMU ratio

[Ionela Voinescu <ionela.voinescu@arm.com>]

Hi,

On Wednesday 18 Oct 2023 at 18:25:40 (+0200), Vincent Guittot wrote:
> Use the new capacity_ref_freq to set the ratio that is used by AMU for
> computing the arch_scale_freq_capacity().
> This helps to keep everything aligned using the same reference for
> computing CPUs capacity.
> 
> The default value of the ratio ensures that arch_scale_freq_capacity()
> returns max capacity until it is set to its correct value with the
> cpu capacity and capacity_ref_freq.
> 
> Signed-off-by: Vincent Guittot <vincent.guittot@linaro.org>
> ---
>  arch/arm64/kernel/topology.c  | 18 ++++++++++--------
>  drivers/base/arch_topology.c  | 14 ++++++++++++--
>  include/linux/arch_topology.h |  1 +
>  3 files changed, 23 insertions(+), 10 deletions(-)
> 
> diff --git a/arch/arm64/kernel/topology.c b/arch/arm64/kernel/topology.c
> index 817d788cd866..0f8f6e90c46d 100644
> --- a/arch/arm64/kernel/topology.c
> +++ b/arch/arm64/kernel/topology.c
> @@ -82,7 +82,12 @@ int __init parse_acpi_topology(void)
>  #undef pr_fmt
>  #define pr_fmt(fmt) "AMU: " fmt
>  
> -static DEFINE_PER_CPU_READ_MOSTLY(unsigned long, arch_max_freq_scale);
> +/*
> + * Ensure that amu_scale_freq_tick() will return SCHED_CAPACITY_SHIFT until
> + * the CPU capacity and its assosciated frequency have been correctly
> + * initialized.

s/SCHED_CAPACITY_SHIFT/SCHED_CAPACITY_SCALE

> + */
> +static DEFINE_PER_CPU_READ_MOSTLY(unsigned long, arch_max_freq_scale) = (2 * SCHED_CAPACITY_SHIFT);

It should be 1UL << (2 * SCHED_CAPACITY_SHIFT).

>  static DEFINE_PER_CPU(u64, arch_const_cycles_prev);
>  static DEFINE_PER_CPU(u64, arch_core_cycles_prev);
>  static cpumask_var_t amu_fie_cpus;
> @@ -112,9 +117,9 @@ static inline bool freq_counters_valid(int cpu)
>  	return true;
>  }
>  
> -static int freq_inv_set_max_ratio(int cpu, u64 max_rate, u64 ref_rate)
> +int freq_inv_set_max_ratio(int cpu, u64 max_rate)
>  {
> -	u64 ratio;
> +	u64 ratio, ref_rate = arch_timer_get_rate();
>  
>  	if (unlikely(!max_rate || !ref_rate)) {
>  		pr_debug("CPU%d: invalid maximum or reference frequency.\n",
> @@ -142,7 +147,7 @@ static int freq_inv_set_max_ratio(int cpu, u64 max_rate, u64 ref_rate)
>  		return -EINVAL;
>  	}

The return value is no longer used so it might be worth declaring it to
return void and WARN_ONCE for unlikely(!max_rate || !ref_rate).

>  
> -	per_cpu(arch_max_freq_scale, cpu) = (unsigned long)ratio;
> +	WRITE_ONCE(per_cpu(arch_max_freq_scale, cpu), (unsigned long)ratio);
>  
>  	return 0;
>  }
> @@ -195,10 +200,7 @@ static void amu_fie_setup(const struct cpumask *cpus)
>  		return;
>  
>  	for_each_cpu(cpu, cpus) {
> -		if (!freq_counters_valid(cpu) ||
> -		    freq_inv_set_max_ratio(cpu,
> -					   cpufreq_get_hw_max_freq(cpu) * 1000ULL,
> -					   arch_timer_get_rate()))
> +		if (!freq_counters_valid(cpu))
>  			return;
>  	}
>  
> diff --git a/drivers/base/arch_topology.c b/drivers/base/arch_topology.c
> index 2372ce791bb4..3a604b77b12d 100644
> --- a/drivers/base/arch_topology.c
> +++ b/drivers/base/arch_topology.c
> @@ -344,6 +344,11 @@ bool __init topology_parse_cpu_capacity(struct device_node *cpu_node, int cpu)
>  	return !ret;
>  }
>  
> +int __weak freq_inv_set_max_ratio(int cpu, u64 max_rate)
> +{
> +	return 0;
> +}
> +
>  #ifdef CONFIG_ACPI_CPPC_LIB
>  #include <acpi/cppc_acpi.h>
>  
> @@ -369,7 +374,6 @@ void topology_init_cpu_capacity_cppc(void)
>  			capacity_scale = max_t(u64, capacity_scale, raw_capacity[cpu]);
>  
>  			per_cpu(capacity_ref_freq, cpu) = cppc_perf_to_khz(&perf_caps, raw_capacity[cpu]);
> -
>  			pr_debug("cpu_capacity: CPU%d cpu_capacity=%u (raw).\n",
>  				 cpu, raw_capacity[cpu]);
>  			continue;
> @@ -381,6 +385,9 @@ void topology_init_cpu_capacity_cppc(void)
>  	}
>  
>  	for_each_possible_cpu(cpu) {
> +		freq_inv_set_max_ratio(cpu,
> +				       per_cpu(capacity_ref_freq, cpu));
> +
>  		capacity = raw_capacity[cpu];
>  		capacity = div64_u64(capacity << SCHED_CAPACITY_SHIFT,
>  				     capacity_scale);
> @@ -422,8 +429,11 @@ init_cpu_capacity_callback(struct notifier_block *nb,
>  
>  	cpumask_andnot(cpus_to_visit, cpus_to_visit, policy->related_cpus);
>  
> -	for_each_cpu(cpu, policy->related_cpus)
> +	for_each_cpu(cpu, policy->related_cpus) {
>  		per_cpu(capacity_ref_freq, cpu) = policy->cpuinfo.max_freq;
> +		freq_inv_set_max_ratio(cpu,
> +				       per_cpu(capacity_ref_freq, cpu));

capacity_ref_freq is in KHz while arch_timer_get_rate() is in Hz. One or
the other needs to be scaled.

The same in topology_init_cpu_capacity_cppc().

Thanks,
Ionela.

> +	}
>  
>  	if (cpumask_empty(cpus_to_visit)) {
>  		topology_normalize_cpu_scale();
> diff --git a/include/linux/arch_topology.h b/include/linux/arch_topology.h
> index 38ca6c76af56..b6e95d763279 100644
> --- a/include/linux/arch_topology.h
> +++ b/include/linux/arch_topology.h
> @@ -99,6 +99,7 @@ void update_siblings_masks(unsigned int cpu);
>  void remove_cpu_topology(unsigned int cpuid);
>  void reset_cpu_topology(void);
>  int parse_acpi_topology(void);
> +int freq_inv_set_max_ratio(int cpu, u64 max_rate);
>  #endif
>  
>  #endif /* _LINUX_ARCH_TOPOLOGY_H_ */
> -- 
> 2.34.1
>