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

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Message-ID: <f5e398f3-fbb7-4840-9084-14c8254b2118@arm.com>
Date:   Wed, 25 Oct 2023 22:13:12 +0200
From:   Dietmar Eggemann <dietmar.eggemann@....com>
To:     Vincent Guittot <vincent.guittot@...aro.org>,
        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, 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
Cc:     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 18/10/2023 18:25, 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@...aro.org>
> Reviewed-by: Lukasz Luba <lukasz.luba@....com>
> Tested-by: Lukasz Luba <lukasz.luba@....com>
> 
> ---
>  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

s/cpufreq_get_capacity_ref_freq/get_capacity_ref_freq

s/of a given CPU/for a given cpufreq policy ? (of which the CPU managing
it is used for the arch_scale_freq_ref() call in the function.

> + * 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.

Looks like use_current does not exists as a parameter.

> + *
> + * 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;
> +}

Reviewed-by: Dietmar Eggemann <dietmar.eggemann@....com>