Re: [PATCH v3 3/6] cpufreq/schedutil: use a fixed reference frequency

[Rafael J. Wysocki]

On Wed, Oct 18, 2023 at 6:25 PM Vincent Guittot
<vincent.guittot@xxxxxxxxxx> 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@xxxxxxxxxx>
> Reviewed-by: Lukasz Luba <lukasz.luba@xxxxxxx>
> Tested-by: Lukasz Luba <lukasz.luba@xxxxxxx>

Acked-by: Rafael J. Wysocki <rafael@xxxxxxxxxx>

>
> ---
>  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 458d359f5991..6e4030482ae8 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;
> +
> +       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)
> --
> 2.34.1
>