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SubjectRe: [PATCH 2/2] thermal: power allocator: estimate sustainable power only once
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Hi Ionela,

On 10/8/20 11:14 AM, Ionela Voinescu wrote:
> Hi Lukasz,
>
> On Friday 02 Oct 2020 at 13:24:16 (+0100), Lukasz Luba wrote:
>> The sustainable power value might come from the Device Tree or can be
>> estimated in run time. There is no need to estimate every time when the
>> governor is called and temperature is high. Instead, store the estimated
>> value and make it available via standard sysfs interface so it can be
>> checked from the user-space.
>>
>> Signed-off-by: Lukasz Luba <lukasz.luba@arm.com>
>> ---
>> drivers/thermal/gov_power_allocator.c | 2 ++
>> 1 file changed, 2 insertions(+)
>>
>> diff --git a/drivers/thermal/gov_power_allocator.c b/drivers/thermal/gov_power_allocator.c
>> index f69fafe486a5..dd59085f38f5 100644
>> --- a/drivers/thermal/gov_power_allocator.c
>> +++ b/drivers/thermal/gov_power_allocator.c
>> @@ -204,6 +204,8 @@ static u32 pid_controller(struct thermal_zone_device *tz,
>> estimate_pid_constants(tz, sustainable_power,
>> params->trip_switch_on, control_temp,
>> true);
>> + /* Do the estimation only once and make available in sysfs */
>> + tz->tzp->sustainable_power = sustainable_power;
>
> After looking over the code, it does seems mostly useless to do the
> estimation every time the controller kicks in.
>
> But I have two comments in this regard:
>
> - The estimation is dependent on the temperature we control for which
> can be changed from sysfs. While I don't see that as a big worry,
> (sustainable power is an estimation anyway), it might be worth a
> more detailed comment on why we don't expect this to be a problem,
> or what we expect the consequences of computing sustainable power
> only once could be.

The problem is that we don't expose the estimated value in the sysfs.
This is the case when there was no DT entry with 'sustainable-power'.
If someone is going to write the values via sysfs, we assume he/she
knows the consequences and also what other values to write and where,
to make it working optimally.

>
> - In the function comment for estimate_pid_constants() there is a
> mention of sustainable power:
> """
> * Sustainable power is provided in case it was estimated. The
> * estimated sustainable_power should not be stored in the
> * thermal_zone_parameters so it has to be passed explicitly to this
> * function.
> """

Good catch, that comment left. I will remove it.

> If we are going to compute the sustainable power estimation only once,
> this comment should be removed, the estimated value should be added to
> the trip point parameters before estimate_pid_constants(), and the
> sustainable_power argument should be removed.
> Otherwise we end up with conflicting information in the code.

We can also call estimate_sustainable_power() inside the
estimate_pid_constants() if sust. power was 0, then set the
tz->tzp->sustainable_power = sustainable_power

Thank you for your comments.

Regards,
Lukasz

>
> Regards,
> Ionela.
>

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