linux-kernel - Re: [PATCH v2 09/16] x86/resctrl: Add detailed descriptions for Clearwater Forest events

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Message-ID: <Z-sSC48XsxFrzlVY@agluck-desk3>
Date: Mon, 31 Mar 2025 15:07:07 -0700
From: "Luck, Tony" <tony.luck@...el.com>
To: Reinette Chatre <reinette.chatre@...el.com>
Cc: Fenghua Yu <fenghuay@...dia.com>,
	Maciej Wieczor-Retman <maciej.wieczor-retman@...el.com>,
	Peter Newman <peternewman@...gle.com>,
	James Morse <james.morse@....com>, Babu Moger <babu.moger@....com>,
	Drew Fustini <dfustini@...libre.com>,
	Dave Martin <Dave.Martin@....com>, linux-kernel@...r.kernel.org,
	patches@...ts.linux.dev
Subject: Re: [PATCH v2 09/16] x86/resctrl: Add detailed descriptions for
 Clearwater Forest events

On Mon, Mar 31, 2025 at 09:21:11AM -0700, Reinette Chatre wrote:
> Hi Tony,
> 
> On 3/21/25 4:15 PM, Tony Luck wrote:
> > There are two event groups one for energy reporting and another
> > for "perf" events.
> > 
> > See the XML description files in https://github.com/intel/Intel-PMT
> > in the xml/CWF/OOBMSM/{RMID-ENERGY,RMID-PERF}/ for the detailed
> > descriptions that were used to derive these descriptions.
> 
> It is unexpected to me that this is made model specific while the
> implementation is built around a guid. What will happen when
> a new system using the same event layout arrives? Will the url
> above be duplicated for this new system's acronym and contain
> duplicate data? How will the resctrl support change? If I understand
> correctly resctrl will not need to be changed but instead the "CWF"
> events will just automatically be used for this new hypothetical
> system? This makes me think that this should not be so CWF specific.

I was told that we might expect to see new guid values to describe
different event register layouts for the same CPU model. The event
aggregators are all firmware driven. So a BIOS update could make changes.

So I've left open the option to add additional structure defintions for
Clearwater Forest with some future firmware update.

If a future processor uses the exact same layout with the same guid value,
then no Linux update would be needed. We'd just have the slight oddity
that a structure named "cwf_*" would match and be used.

Next system to implement these telemetry events has a very different
list of supported events.

> Reinette

-Tony