linux-kernel - RE: [RFC PATCH v3 2/2] cpuidle: teo: Introduce util-awareness

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Message-ID: <002401d90108$93a831e0$baf895a0$@telus.net>
Date:   Fri, 25 Nov 2022 12:00:32 -0800
From:   "Doug Smythies" <dsmythies@...us.net>
To:     "'Rafael J. Wysocki'" <rafael@...nel.org>,
        "'Kajetan Puchalski'" <kajetan.puchalski@....com>
Cc:     <daniel.lezcano@...aro.org>, <lukasz.luba@....com>,
        <Dietmar.Eggemann@....com>, <yu.chen.surf@...il.com>,
        <linux-pm@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
        "Doug Smythies" <dsmythies@...us.net>
Subject: RE: [RFC PATCH v3 2/2] cpuidle: teo: Introduce util-awareness

On 2022.11.25 10:27 Rafael wrote:
> On Mon, Oct 31, 2022 at 1:14 PM Kajetan wrote:

... [delete some] ...

>> +}
>> +
>> /**
>>   * teo_update - Update CPU metrics after wakeup.
>>   * @drv: cpuidle driver containing state data.
>> @@ -303,7 +359,9 @@ static int teo_select(struct cpuidle_driver *drv, struct cpuidle_device *dev,
>>         int i;
>>
>>         if (dev->last_state_idx >= 0) {
>> -               teo_update(drv, dev);
>> +               /* don't update metrics if the cpu was utilized during the last sleep */
>
> Why?
>
> The metrics are related to idle duration and cpu_data->utilized
> indicates whether or not latency should be reduced.  These are
> different things.
>
> Moreover, this is just one data point and there may not be any direct
> connection between it and the decision made in this particular cycle.

Hi Rafael,

Yes, agreed. And version 4 of this patch set deleted this stuff.
See also my similar feedback, with accompanying test data
that verified the issue in [1].

[1] https://lore.kernel.org/linux-pm/CAAYoRsUgm6KyJCDowGKFVuMwJepnVN8NFEenjd3O-FN7+BETSw@mail.gmail.com/

... Doug