Re: [PATCH V4] thermal/core/power_allocator: reset thermal governor when trip point is changed

[Lukasz Luba]

On 6/25/23 09:39, Di Shen wrote:
> On Fri, Jun 23, 2023 at 4:10 PM Lukasz Luba <lukasz.luba@xxxxxxx> wrote:
> > On 6/22/23 19:27, Rafael J. Wysocki wrote:

[snip]

> > > So there seems to be a claim that IPA is the only governor needing the
> > > ->reset() callback, but I have not seen any solid analysis confirming
> > > that.  It very well may be the case, but then the changelog should
> > > clearly explain why this is the case IMO.
> >
> > I agree, the patch header doesn't explain that properly. Here is the
> > explanation for this Intelligent Power Allocator (IPA):
> >
> > The IPA controls temperature using PID mechanism. It's a closed
> > feedback loop. That algorithm can 'learn' from the 'observed'
> > in the past reaction for it's control decisions and accumulates that
> > information in the part called 'error integral'. Those accumulated
> > 'error' gaps are the differences between the set target value and the
> > actually achieved value. In our case the target value is the target
> > temperature which is coming from the trip point. That part is then used
> > with the 'I' (of PID) component, so we can compensate for those
> > 'learned' mistakes.
> > Now, when you change the target temperature value - all your previous
> > learned errors won't help you. That's why Intelligent Power Allocator
> > should reset previously accumulated history.
>
> Yes, THAT's the point!
> Maybe I need to write the commit message in more detail.

Yes, please extend that description.

Regards,
Lukasz