linux-kernel - Re: [PATCH v3 1/3] thermal: cpufreq_cooling: Update also offline CPUs per-cpu thermal

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Date:   Mon, 14 Jun 2021 11:21:16 +0100
From:   Lukasz Luba <lukasz.luba@....com>
To:     Viresh Kumar <viresh.kumar@...aro.org>
Cc:     linux-kernel@...r.kernel.org, linux-pm@...r.kernel.org,
        peterz@...radead.org, rjw@...ysocki.net,
        vincent.guittot@...aro.org, qperret@...gle.com,
        dietmar.eggemann@....com, vincent.donnefort@....com,
        Beata.Michalska@....com, mingo@...hat.com, juri.lelli@...hat.com,
        rostedt@...dmis.org, segall@...gle.com, mgorman@...e.de,
        bristot@...hat.com, thara.gopinath@...aro.org,
        amit.kachhap@...il.com, amitk@...nel.org, rui.zhang@...el.com,
        daniel.lezcano@...aro.org
Subject: Re: [PATCH v3 1/3] thermal: cpufreq_cooling: Update also offline CPUs
 per-cpu thermal_pressure



On 6/14/21 11:12 AM, Viresh Kumar wrote:
> On 10-06-21, 16:03, Lukasz Luba wrote:
>> The thermal pressure signal gives information to the scheduler about
>> reduced CPU capacity due to thermal. It is based on a value stored in a
>> per-cpu 'thermal_pressure' variable. The online CPUs will get the new
>> value there, while the offline won't. Unfortunately, when the CPU is back
>> online, the value read from per-cpu variable might be wrong (stale data).
>> This might affect the scheduler decisions, since it sees the CPU capacity
>> differently than what is actually available.
>>
>> Fix it by making sure that all online+offline CPUs would get the proper
>> value in their per-cpu variable when thermal framework sets capping.
>>
>> Fixes: f12e4f66ab6a3 ("thermal/cpu-cooling: Update thermal pressure in case of a maximum frequency capping")
>> Signed-off-by: Lukasz Luba <lukasz.luba@....com>
>> ---
>>   drivers/thermal/cpufreq_cooling.c | 2 +-
>>   1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> diff --git a/drivers/thermal/cpufreq_cooling.c b/drivers/thermal/cpufreq_cooling.c
>> index eeb4e4b76c0b..43b1ae8a7789 100644
>> --- a/drivers/thermal/cpufreq_cooling.c
>> +++ b/drivers/thermal/cpufreq_cooling.c
>> @@ -478,7 +478,7 @@ static int cpufreq_set_cur_state(struct thermal_cooling_device *cdev,
>>   	ret = freq_qos_update_request(&cpufreq_cdev->qos_req, frequency);
>>   	if (ret >= 0) {
>>   		cpufreq_cdev->cpufreq_state = state;
>> -		cpus = cpufreq_cdev->policy->cpus;
>> +		cpus = cpufreq_cdev->policy->related_cpus;
>>   		max_capacity = arch_scale_cpu_capacity(cpumask_first(cpus));
>>   		capacity = frequency * max_capacity;
>>   		capacity /= cpufreq_cdev->policy->cpuinfo.max_freq;
> 
> Acked-by: Viresh Kumar <viresh.kumar@...aro.org>
> 

Thank you Viresh!

Regards,
Lukasz