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

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Date:   Thu, 6 Oct 2022 18:14:59 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     "Brown, Len" <len.brown@...el.com>
Cc:     Ricardo Neri <ricardo.neri-calderon@...ux.intel.com>,
        Juri Lelli <juri.lelli@...hat.com>,
        Vincent Guittot <vincent.guittot@...aro.org>,
        "Neri, Ricardo" <ricardo.neri@...el.com>,
        "Shankar, Ravi V" <ravi.v.shankar@...el.com>,
        Ben Segall <bsegall@...gle.com>,
        Daniel Bristot de Oliveira <bristot@...hat.com>,
        Dietmar Eggemann <dietmar.eggemann@....com>,
        Mel Gorman <mgorman@...e.de>,
        "Wysocki, Rafael J" <rafael.j.wysocki@...el.com>,
        Srinivas Pandruvada <srinivas.pandruvada@...ux.intel.com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Tim Chen <tim.c.chen@...ux.intel.com>,
        Valentin Schneider <vschneid@...hat.com>,
        "x86@...nel.org" <x86@...nel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "Chen, Tim C" <tim.c.chen@...el.com>
Subject: Re: [RFC PATCH 15/23] thermal: intel: hfi: Report per-cpu
 class-specific performance scores

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.