linux-kernel - Re: [PATCH] sched/cpufreq: Ensure sd is rebuilt for EAS check

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Message-ID: <872c894d-1caa-4752-bb6a-08c29f1fb3ad@arm.com>
Date: Wed, 13 Nov 2024 12:53:21 +0100
From: Pierre Gondois <pierre.gondois@....com>
To: Christian Loehle <christian.loehle@....com>,
 "Rafael J. Wysocki" <rafael@...nel.org>
Cc: Dietmar Eggemann <dietmar.eggemann@....com>,
 Peter Zijlstra <peterz@...radead.org>,
 Vincent Guittot <vincent.guittot@...aro.org>,
 Viresh Kumar <viresh.kumar@...aro.org>,
 "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
 linux-pm <linux-pm@...r.kernel.org>, Ingo Molnar <mingo@...hat.com>,
 Valentin Schneider <vschneid@...hat.com>
Subject: Re: [PATCH] sched/cpufreq: Ensure sd is rebuilt for EAS check

I could reproduce the issue on an ACPI/CPPC based platform.

It seems the reason it doesn't work is that for CPPC,
CPUFREQ_HAVE_GOVERNOR_PER_POLICY is not set. So
   kernel/sched/cpufreq_schedutil.c::global_tunables
is set and we don't bail out in sugov_init().

On a system with CPUFREQ_HAVE_GOVERNOR_PER_POLICY set,
the issue is not triggered. sugov_eas_rebuild_sd() is always called.

The patch effectively solved the issue for me.

Regards,
Pierre

On 11/9/24 01:24, Christian Loehle wrote:
> Ensure sugov_eas_rebuild_sd() is always called when sugov_init()
> succeeds. The out goto initialized sugov without forcing the rebuild.
> 
> Previously the missing call to sugov_eas_rebuild_sd() could lead to EAS
> not being enabled on boot when it should have been, because it requires
> all policies to be controlled by schedutil while they might not have
> been initialized yet.
> 
> Fixes: e7a1b32e43b1 ("cpufreq: Rebuild sched-domains when removing cpufreq driver")
> Signed-off-by: Christian Loehle <christian.loehle@....com>
> ---
>   kernel/sched/cpufreq_schedutil.c | 3 +--
>   1 file changed, 1 insertion(+), 2 deletions(-)
> 
> diff --git a/kernel/sched/cpufreq_schedutil.c b/kernel/sched/cpufreq_schedutil.c
> index c6ba15388ea7..28c77904ea74 100644
> --- a/kernel/sched/cpufreq_schedutil.c
> +++ b/kernel/sched/cpufreq_schedutil.c
> @@ -783,9 +783,8 @@ static int sugov_init(struct cpufreq_policy *policy)
>   	if (ret)
>   		goto fail;
>   
> -	sugov_eas_rebuild_sd();
> -
>   out:
> +	sugov_eas_rebuild_sd();
>   	mutex_unlock(&global_tunables_lock);
>   	return 0;
>