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Date: Mon, 16 Dec 2024 15:49:14 +0100
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Subject: Re: [RFC][PATCH v021 4/9] sched/topology: Adjust cpufreq checks for
 EAS
To: "Rafael J. Wysocki" <rjw@rjwysocki.net>,
 Linux PM <linux-pm@vger.kernel.org>
Cc: LKML <linux-kernel@vger.kernel.org>, Lukasz Luba <lukasz.luba@arm.com>,
 Peter Zijlstra <peterz@infradead.org>,
 Srinivas Pandruvada <srinivas.pandruvada@linux.intel.com>,
 Morten Rasmussen <morten.rasmussen@arm.com>,
 Vincent Guittot <vincent.guittot@linaro.org>,
 Ricardo Neri <ricardo.neri-calderon@linux.intel.com>,
 Pierre Gondois <pierre.gondois@arm.com>
References: <5861970.DvuYhMxLoT@rjwysocki.net>
 <2989520.e9J7NaK4W3@rjwysocki.net>
From: Dietmar Eggemann <dietmar.eggemann@arm.com>
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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.