linux-kernel - Re: [RFT][PATCH v1 3/8] cpufreq/sched: Allow .setpolicy() cpufreq drivers to enable EAS

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Message-ID: <e439a75c-fe36-4fba-b394-c154adeff15a@arm.com>
Date: Thu, 17 Apr 2025 13:19:39 +0100
From: Christian Loehle <christian.loehle@....com>
To: "Rafael J. Wysocki" <rjw@...ysocki.net>,
 Linux PM <linux-pm@...r.kernel.org>
Cc: LKML <linux-kernel@...r.kernel.org>, Lukasz Luba <lukasz.luba@....com>,
 Peter Zijlstra <peterz@...radead.org>,
 Srinivas Pandruvada <srinivas.pandruvada@...ux.intel.com>,
 Dietmar Eggemann <dietmar.eggemann@....com>,
 Morten Rasmussen <morten.rasmussen@....com>,
 Vincent Guittot <vincent.guittot@...aro.org>,
 Ricardo Neri <ricardo.neri-calderon@...ux.intel.com>,
 Pierre Gondois <pierre.gondois@....com>
Subject: Re: [RFT][PATCH v1 3/8] cpufreq/sched: Allow .setpolicy() cpufreq
 drivers to enable EAS

On 4/16/25 19:01, Rafael J. Wysocki wrote:
> From: Rafael J. Wysocki <rafael.j.wysocki@...el.com>
> 
> Some cpufreq drivers, like intel_pstate, have built-in governors that
> are used instead of regular cpufreq governors, schedutil in particular,
> but they can work with EAS just fine, so allow EAS to be used with
> those drivers.
> 
> Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@...el.com>
> ---
> 
> v0.3 -> v1
>      * Rebase on top of the new [1-2/8].
>      * Update the diagnostic message printed if the conditions are not met.
> 
> This patch is regarded as a cleanup for 6.16.
> 
> ---
>  drivers/cpufreq/cpufreq.c |   13 +++++++++++--
>  1 file changed, 11 insertions(+), 2 deletions(-)
> 
> --- a/drivers/cpufreq/cpufreq.c
> +++ b/drivers/cpufreq/cpufreq.c
> @@ -3054,7 +3054,16 @@
>  
>  	guard(cpufreq_policy_read)(policy);
>  
> -	return sugov_is_governor(policy);
> +	/*
> +	 * For EAS compatibility, require that either schedutil is the policy
> +	 * governor or the policy is governed directly by the cpufreq driver.
> +	 *
> +	 * In the latter case, it is assumed that EAS can only be enabled by the
> +	 * cpufreq driver itself which will not enable EAS if it does not meet
> +	 * the EAS' expectations regarding performance scaling response.
> +	 */
> +	return sugov_is_governor(policy) || (!policy->governor &&
> +		policy->policy != CPUFREQ_POLICY_UNKNOWN);
>  }
>  
>  bool cpufreq_ready_for_eas(const struct cpumask *cpu_mask)
> @@ -3064,7 +3073,7 @@
>  	/* Do not attempt EAS if schedutil is not being used. */
>  	for_each_cpu(cpu, cpu_mask) {
>  		if (!cpufreq_policy_is_good_for_eas(cpu)) {
> -			pr_debug("rd %*pbl: schedutil is mandatory for EAS\n",
> +			pr_debug("rd %*pbl: EAS requirements not met\n",
>  				 cpumask_pr_args(cpu_mask));

I'd prefer to have at least "EAS cpufreq requirements" printed here.
with that caveat
Reviewed-by: Christian Loehle <christian.loehle@....com>

Maybe we should amend the EAS documentation to reflect this?
(And also emphasise that EAS will make cpufreq assumptions as if sugov
was the governor regardless.)

>  			return false;
>  		}
> 
> 
>