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

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Message-ID: <CAJZ5v0gLv1ybYWM4BfmXoW5cHtZXW3tUL+PoXDKQqSBa2UCj0w@mail.gmail.com>
Date: Mon, 16 Dec 2024 15:58:09 +0100
From: "Rafael J. Wysocki" <rafael@...nel.org>
To: Dietmar Eggemann <dietmar.eggemann@....com>
Cc: "Rafael J. Wysocki" <rjw@...ysocki.net>, Linux PM <linux-pm@...r.kernel.org>, 
	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 Mon, Dec 16, 2024 at 3:49 PM Dietmar Eggemann
<dietmar.eggemann@....com> wrote:
>
> 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.

Fair enough.

I'm considering a patch moving these checks to cpufreq, then I'll
change all of that.