linux-kernel - Re: [PATCH] cpufreq: Rebuild sched-domains when removing cpufreq driver

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Message-ID: <ebc8f4cd-1ac6-e7c8-8e20-53bca964ce56@arm.com>
Date:   Tue, 19 Sep 2023 01:03:52 +0200
From:   Dietmar Eggemann <dietmar.eggemann@....com>
To:     Pierre Gondois <pierre.gondois@....com>,
        linux-kernel@...r.kernel.org
Cc:     Shrikanth Hegde <sshegde@...ux.vnet.ibm.com>, vschneid@...hat.com,
        "Rafael J. Wysocki" <rafael@...nel.org>,
        Viresh Kumar <viresh.kumar@...aro.org>,
        linux-pm@...r.kernel.org
Subject: Re: [PATCH] cpufreq: Rebuild sched-domains when removing cpufreq
 driver

On 18/09/2023 13:29, Pierre Gondois wrote:
> The Energy Aware Scheduler (EAS) relies on the schedutil governor.
> When moving to/from the schedutil governor, sched domains must be
> rebuilt to allow re-evaluating the enablement conditions of EAS.
> This is done through sched_cpufreq_governor_change().
> 
> Having a cpufreq governor assumes having a cpufreq driver running.
> Inserting/removing a cpufreq driver should trigger a re-evaluation
> of EAS enablement conditions, avoiding to see EAS enabled when
> removing a running cpufreq driver.
> 
> Add a sched_cpufreq_governor_change() call in cpufreq driver removal
> path.

Rebuilding SDs when inserting the driver is already covered by

  cpufreq_online()
    cpufreq_set_policy()
      sched_cpufreq_governor_change()
        if (old or new gov eq. schedutil)
          schedule_work(&rebuild_sd_work)

So what's missing is only a sched_cpufreq_governor_change() call when
removing the driver, right?

> 
> Signed-off-by: Pierre Gondois <pierre.gondois@....com>
> ---
>  drivers/cpufreq/cpufreq.c | 2 ++
>  1 file changed, 2 insertions(+)
> 
> diff --git a/drivers/cpufreq/cpufreq.c b/drivers/cpufreq/cpufreq.c
> index 60ed89000e82..0a4979c34fd1 100644
> --- a/drivers/cpufreq/cpufreq.c
> +++ b/drivers/cpufreq/cpufreq.c
> @@ -1673,6 +1673,8 @@ static void __cpufreq_offline(unsigned int cpu, struct cpufreq_policy *policy)
>  		cpufreq_driver->exit(policy);
>  		policy->freq_table = NULL;
>  	}
> +
> +	sched_cpufreq_governor_change(policy, policy->governor);
>  }
>  
>  static int cpufreq_offline(unsigned int cpu)