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

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Message-ID: <e25d912a-906d-82da-5b09-f2256ebfbfe3@arm.com>
Date:   Tue, 19 Sep 2023 09:49:45 +0200
From:   Pierre Gondois <pierre.gondois@....com>
To:     Dietmar Eggemann <dietmar.eggemann@....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 9/19/23 01:03, Dietmar Eggemann wrote:
> 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?

Yes exact, removing a cpufreq driver (e.g. `rmmod cppc_cpufreq.ko`) goes
through:
cpufreq_remove_dev()
\-__cpufreq_offline()

so the path you mentioned is not used in this case.

Regards,
Pierre