Re: [RFC PATCH 15/23] thermal: intel: hfi: Report per-cpu class-specific performance scores

Peter Zijlstra
2022-10-06T16:15:30Z

On Thu, Oct 06, 2022 at 03:05:18PM +0000, Brown, Len wrote:
> > > > Does any of that data actually ever change? Isn't the class score
> > > > fixed per CPU type?
>
> Depends on the chip.
>
> As we described at LPC, the ADL chips shipping today update their
> tables in response to RAPL working to keep the system below PL1.
> Linux or user-space can scribble on PL1 at any time, so technically,
> this table update can happen at any time.
>
> That said, it is true that, say, an ADL desktop part that operates
> with plenty of power and cooling will send the initial table and never
> have a need to update the table after that.

I have a NUC, so laptop part with limited thermals (the Lenovo P360
Ultra was announed just after I ordered the P360 Tiny). Still I wasn't
able to trigger this during normal operation.

> Upcoming chips are smarter and will give us more dynamic information.
> We expect the P-unit to send only "meaningful" changes, and that they
> Shall not occur more often than every 10ms.

Make *very* sure those upcoming chips don't broadcast that interrupt.
Broadcast interrupts are unconditional crap.

Broadcast interrupts every 10ms is terrifying crap and a good reason for
people to force disable this stuff.