Re: [PATCH v2 4/6] cpufreq/schedutil: use a fixed reference frequency

[Lukasz Luba <lukasz.luba@arm.com>]

On 10/9/23 11:36, Vincent Guittot wrote:
> cpuinfo.max_freq can change at runtime because of boost as an example. This
> implies that the value could be different than the one that has been
> used when computing the capacity of a CPU.
> 
> The new arch_scale_freq_ref() returns a fixed and coherent reference
> frequency that can be used when computing a frequency based on utilization.
> 
> Use this arch_scale_freq_ref() when available and fallback to
> policy otherwise.
> 
> Signed-off-by: Vincent Guittot <vincent.guittot@linaro.org>
> ---
>   kernel/sched/cpufreq_schedutil.c | 26 ++++++++++++++++++++++++--
>   1 file changed, 24 insertions(+), 2 deletions(-)
> 
> diff --git a/kernel/sched/cpufreq_schedutil.c b/kernel/sched/cpufreq_schedutil.c
> index 4492608b7d7f..1fa7e74add8f 100644
> --- a/kernel/sched/cpufreq_schedutil.c
> +++ b/kernel/sched/cpufreq_schedutil.c
> @@ -114,6 +114,28 @@ static void sugov_deferred_update(struct sugov_policy *sg_policy)
>   	}
>   }
>   
> +/**
> + * cpufreq_get_capacity_ref_freq - get the reference frequency of a given CPU that
> + * has been used to correlate frequency and compute capacity.
> + * @policy: the cpufreq policy of the CPU in question.
> + * @use_current: Fallback to current freq instead of policy->cpuinfo.max_freq.
> + *
> + * Return: the reference CPU frequency to compute a capacity.
> + */
> +static __always_inline
> +unsigned long get_capacity_ref_freq(struct cpufreq_policy *policy)
> +{
> +	unsigned int freq = arch_scale_freq_ref(policy->cpu);
> +
> +	if (freq)
> +		return freq;

Looks good, for the platforms having this inline function returning 0,
this will be optimized out.

> +
> +	if (arch_scale_freq_invariant())
> +		return policy->cpuinfo.max_freq;
> +
> +	return policy->cur;
> +}
> +
>   /**
>    * get_next_freq - Compute a new frequency for a given cpufreq policy.
>    * @sg_policy: schedutil policy object to compute the new frequency for.
> @@ -140,10 +162,10 @@ static unsigned int get_next_freq(struct sugov_policy *sg_policy,
>   				  unsigned long util, unsigned long max)
>   {
>   	struct cpufreq_policy *policy = sg_policy->policy;
> -	unsigned int freq = arch_scale_freq_invariant() ?
> -				policy->cpuinfo.max_freq : policy->cur;
> +	unsigned int freq;
>   
>   	util = map_util_perf(util);
> +	freq = get_capacity_ref_freq(policy);
>   	freq = map_util_freq(util, freq, max);
>   
>   	if (freq == sg_policy->cached_raw_freq && !sg_policy->need_freq_update)


Reviewed-by: Lukasz Luba <lukasz.luba@arm.com>

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