linux-kernel - Re: [RFC][PATCH v021 4/9] sched/topology: Adjust cpufreq checks for EAS

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Message-ID: <7ca98023-df18-4973-8c4f-18ab381b7aba@arm.com>
Date: Mon, 16 Dec 2024 15:49:14 +0100
From: Dietmar Eggemann <dietmar.eggemann@....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>,
 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: [RFC][PATCH v021 4/9] sched/topology: Adjust cpufreq checks for
 EAS

On 29/11/2024 17:00, Rafael J. Wysocki wrote:

[...]

> @@ -261,11 +262,14 @@ static bool sched_is_eas_possible(const
>  			}
>  			return false;
>  		}
> +		/* Require schedutil or a "setpolicy" driver */
>  		gov = policy->governor;
> +		cpufreq_ok = gov == &schedutil_gov ||
> +				(!gov && policy->policy != CPUFREQ_POLICY_UNKNOWN);
>  		cpufreq_cpu_put(policy);
> -		if (gov != &schedutil_gov) {
> +		if (!cpufreq_ok) {
>  			if (sched_debug()) {
> -				pr_info("rd %*pbl: Checking EAS, schedutil is mandatory\n",
> +				pr_info("rd %*pbl: Checking EAS, unsuitable cpufreq governor\n",
>  					cpumask_pr_args(cpu_mask));
>  			}
>  			return false;

build_perf_domains() which calls sched_is_eas_possible() has schedutil
(4) mentioned in the function header as well:

/*
 * EAS can be used on a root domain if it meets all the following
conditions:
 *    1. an Energy Model (EM) is available;
 *    2. the SD_ASYM_CPUCAPACITY flag is set in the sched_domain hierarchy.
 *    3. no SMT is detected.
 *    4. schedutil is driving the frequency of all CPUs of the rd; <-- !
 *    5. frequency invariance support is present;
 */

IMHO, his patch should remove the function header since the conditions
in sched_is_eas_possible() have comments already or are self-explanatory.