linux-kernel - Re: [Patch v4 5/6] thermal/cpu-cooling: Update thermal pressure in case of a maximum frequency capping

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Date:   Fri, 1 Nov 2019 17:04:47 -0400
From:   Thara Gopinath <thara.gopinath@...aro.org>
To:     Ionela Voinescu <ionela.voinescu@....com>,
        Vincent Guittot <vincent.guittot@...aro.org>
Cc:     Dietmar Eggemann <dietmar.eggemann@....com>,
        Ingo Molnar <mingo@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Zhang Rui <rui.zhang@...el.com>,
        Eduardo Valentin <edubezval@...il.com>,
        Quentin Perret <qperret@...gle.com>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        Amit Kachhap <amit.kachhap@...il.com>,
        Javi Merino <javi.merino@...nel.org>,
        Daniel Lezcano <daniel.lezcano@...aro.org>
Subject: Re: [Patch v4 5/6] thermal/cpu-cooling: Update thermal pressure in
 case of a maximum frequency capping

On 11/01/2019 11:47 AM, Ionela Voinescu wrote:
> Hi guys,
> 
> On Thursday 31 Oct 2019 at 17:38:25 (+0100), Vincent Guittot wrote:
>> On Thu, 31 Oct 2019 at 17:29, Dietmar Eggemann <dietmar.eggemann@....com> wrote:
>>>
>>> On 22.10.19 22:34, Thara Gopinath wrote:
>>>> Thermal governors can request for a cpu's maximum supported frequency
>>>> to be capped in case of an overheat event. This in turn means that the
>>>> maximum capacity available for tasks to run on the particular cpu is
>>>> reduced. Delta between the original maximum capacity and capped
>>>> maximum capacity is known as thermal pressure. Enable cpufreq cooling
>>>> device to update the thermal pressure in event of a capped
>>>> maximum frequency.
>>>>
>>>> Signed-off-by: Thara Gopinath <thara.gopinath@...aro.org>
>>>> ---
>>>>  drivers/thermal/cpu_cooling.c | 31 +++++++++++++++++++++++++++++--
>>>>  1 file changed, 29 insertions(+), 2 deletions(-)
>>>>
>>>> diff --git a/drivers/thermal/cpu_cooling.c b/drivers/thermal/cpu_cooling.c
>>>> index 391f397..2e6a979 100644
>>>> --- a/drivers/thermal/cpu_cooling.c
>>>> +++ b/drivers/thermal/cpu_cooling.c
>>>> @@ -218,6 +218,23 @@ static u32 cpu_power_to_freq(struct cpufreq_cooling_device *cpufreq_cdev,
>>>>  }
>>>>
>>>>  /**
>>>> + * update_sched_max_capacity - update scheduler about change in cpu
>>>> + *                                   max frequency.
>>>> + * @policy - cpufreq policy whose max frequency is capped.
>>>> + */
>>>> +static void update_sched_max_capacity(struct cpumask *cpus,
>>>> +                                   unsigned int cur_max_freq,
>>>> +                                   unsigned int max_freq)
>>>> +{
>>>> +     int cpu;
>>>> +     unsigned long capacity = (cur_max_freq << SCHED_CAPACITY_SHIFT) /
>>>> +                               max_freq;
>>>> +
>>>> +     for_each_cpu(cpu, cpus)
>>>> +             update_thermal_pressure(cpu, capacity);
>>>> +}
>>>> +
>>>> +/**
>>>>   * get_load() - get load for a cpu since last updated
>>>>   * @cpufreq_cdev:    &struct cpufreq_cooling_device for this cpu
>>>>   * @cpu:     cpu number
>>>> @@ -320,6 +337,7 @@ static int cpufreq_set_cur_state(struct thermal_cooling_device *cdev,
>>>>                                unsigned long state)
>>>>  {
>>>>       struct cpufreq_cooling_device *cpufreq_cdev = cdev->devdata;
>>>> +     int ret;
>>>>
>>>>       /* Request state should be less than max_level */
>>>>       if (WARN_ON(state > cpufreq_cdev->max_level))
>>>> @@ -331,8 +349,17 @@ static int cpufreq_set_cur_state(struct thermal_cooling_device *cdev,
>>>>
>>>>       cpufreq_cdev->cpufreq_state = state;
>>>>
>>>> -     return dev_pm_qos_update_request(&cpufreq_cdev->qos_req,
>>>> -                             cpufreq_cdev->freq_table[state].frequency);
>>>> +     ret = dev_pm_qos_update_request
>>>> +                             (&cpufreq_cdev->qos_req,
>>>> +                              cpufreq_cdev->freq_table[state].frequency);
>>>> +
>>>> +     if (ret > 0)
>>>> +             update_sched_max_capacity
>>>> +                             (cpufreq_cdev->policy->cpus,
>>>> +                              cpufreq_cdev->freq_table[state].frequency,
>>>> +                              cpufreq_cdev->policy->cpuinfo.max_freq);
>>>> +
>>>> +     return ret;
>>>>  }
>>>>
>>>>  /**
>>>>
>>>
>>> Why not getting rid of update_sched_max_capacity() entirely and call
>>> update_thermal_pressure() in cpu_cooling.c directly? Saves one level in
>>> the call chain and would mean less code for this feature.
>>
>> But you add complexity in update_thermal_pressure which now has to
>> deal with a cpumask and to compute some frequency ratio
>> IMHO, it's cleaner to keep update_thermal_pressure simple as it is now
>>
> 
> How about removing update_thermal_pressure altogether and doing all the
> work in update_sched_max_capacity? That is, have
> update_sched_max_capacity compute the capped_freq_ratio, do the
> normalization, and set it per_cpu for all CPUs in the frequency domain.
> You'll save some calculations that you're now doing in
> update_thermal_pressure for each cpu and you avoid shifting back and
> forth.

Yes.  I can pass the delta to update_thermal_pressure. I will still want
to keep update_thermal_pressure and a per cpu variable in fair.c to
store this.
> 
> If you're doing so it would be worth renaming update_sched_max_capacity
> to something like update_sched_thermal_pressure.
Will do.


-- 
Warm Regards
Thara