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

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Message-ID: <CAJZ5v0i58HLmgp=JYCbq5B6LUe0tEAhd9Ed9WKqkkHjVEO_W6A@mail.gmail.com>
Date:   Wed, 18 Oct 2023 19:22:40 +0200
From:   "Rafael J. Wysocki" <rafael@...nel.org>
To:     Vincent Guittot <vincent.guittot@...aro.org>
Cc:     linux@...linux.org.uk, catalin.marinas@....com, will@...nel.org,
        paul.walmsley@...ive.com, palmer@...belt.com,
        aou@...s.berkeley.edu, sudeep.holla@....com,
        gregkh@...uxfoundation.org, rafael@...nel.org, mingo@...hat.com,
        peterz@...radead.org, juri.lelli@...hat.com,
        dietmar.eggemann@....com, rostedt@...dmis.org, bsegall@...gle.com,
        mgorman@...e.de, bristot@...hat.com, vschneid@...hat.com,
        viresh.kumar@...aro.org, lenb@...nel.org, robert.moore@...el.com,
        lukasz.luba@....com, ionela.voinescu@....com,
        pierre.gondois@....com, linux-arm-kernel@...ts.infradead.org,
        linux-kernel@...r.kernel.org, linux-riscv@...ts.infradead.org,
        linux-pm@...r.kernel.org, linux-acpi@...r.kernel.org,
        acpica-devel@...ts.linuxfoundation.org, conor.dooley@...rochip.com,
        suagrfillet@...il.com, ajones@...tanamicro.com, lftan@...nel.org
Subject: Re: [PATCH v3 3/6] cpufreq/schedutil: use a fixed reference frequency

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

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