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

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Message-ID: <459cbf79-e493-4caf-9601-d5c477734673@arm.com>
Date: Thu, 17 Apr 2025 14:03:41 +0100
From: Christian Loehle <christian.loehle@....com>
To: "Rafael J. Wysocki" <rafael@...nel.org>
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>,
 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 4/17/25 14:01, Rafael J. Wysocki wrote:
> On Thu, Apr 17, 2025 at 2:19 PM Christian Loehle
> <christian.loehle@....com> wrote:
>>
>> 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.
> 
> Sure.
> 
>> with that caveat
>> Reviewed-by: Christian Loehle <christian.loehle@....com>
>>
>> Maybe we should amend the EAS documentation to reflect this?
> 
> Yes, the documentation should be updated.  Which piece of it in
> particular I need to look at?

Documentation/scheduler/sched-energy.rst
has:
6.4 - Schedutil governor
so at least there.