Messages in this thread | | | Subject | Re: [PATCH 2/2] thermal: power allocator: estimate sustainable power only once | From | Lukasz Luba <> | Date | Thu, 8 Oct 2020 13:34:40 +0100 |
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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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