linux-kernel - Re: [PATCH 1/4] cpufreq: Add a cpufreq pressure feedback for the scheduler

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Message-ID: <af7b67d1-c4a3-44e3-a632-5f0a4ea6eb25@arm.com>
Date:   Thu, 14 Dec 2023 09:21:11 +0000
From:   Lukasz Luba <lukasz.luba@....com>
To:     Vincent Guittot <vincent.guittot@...aro.org>
Cc:     catalin.marinas@....com, will@...nel.org,
        daniel.lezcano@...aro.org, mhiramat@...nel.org,
        rui.zhang@...el.com, vschneid@...hat.com, bristot@...hat.com,
        bsegall@...gle.com, dietmar.eggemann@....com,
        juri.lelli@...hat.com, peterz@...radead.org, mingo@...hat.com,
        linux-arm-msm@...r.kernel.org, linux-pm@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org, agross@...nel.org,
        konrad.dybcio@...aro.org, andersson@...nel.org,
        viresh.kumar@...aro.org, sudeep.holla@....com, rafael@...nel.org,
        rostedt@...dmis.org, mgorman@...e.de, amit.kachhap@...il.com,
        linux-kernel@...r.kernel.org, linux-trace-kernel@...r.kernel.org
Subject: Re: [PATCH 1/4] cpufreq: Add a cpufreq pressure feedback for the
 scheduler



On 12/12/23 14:27, Vincent Guittot wrote:
> Provide to the scheduler a feedback about the temporary max available
> capacity. Unlike arch_update_thermal_pressure, this doesn't need to be
> filtered as the pressure will happen for dozens ms or more.
> 
> Signed-off-by: Vincent Guittot <vincent.guittot@...aro.org>
> ---
>   drivers/cpufreq/cpufreq.c | 48 +++++++++++++++++++++++++++++++++++++++
>   include/linux/cpufreq.h   | 10 ++++++++
>   2 files changed, 58 insertions(+)
> 
> diff --git a/drivers/cpufreq/cpufreq.c b/drivers/cpufreq/cpufreq.c
> index 44db4f59c4cc..7d5f71be8d29 100644
> --- a/drivers/cpufreq/cpufreq.c
> +++ b/drivers/cpufreq/cpufreq.c
> @@ -2563,6 +2563,50 @@ int cpufreq_get_policy(struct cpufreq_policy *policy, unsigned int cpu)
>   }
>   EXPORT_SYMBOL(cpufreq_get_policy);
>   
> +DEFINE_PER_CPU(unsigned long, cpufreq_pressure);
> +EXPORT_PER_CPU_SYMBOL_GPL(cpufreq_pressure);

Why do we export this variable when we have get/update functions?
Do we expect modules would manipulate those per-cpu variables
independently and not like we do per-cpumask in the update func.?