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

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Message-ID: <ff5f3d28-c67b-4b2f-9972-8b12a3a64a29@intel.com>
Date: Mon, 31 Mar 2025 17:13:26 -0700
From: Reinette Chatre <reinette.chatre@...el.com>
To: "Luck, Tony" <tony.luck@...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

Hi Tony,

On 3/31/25 3:07 PM, Luck, Tony wrote:
> 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.

Sounds like this supports my point. Naming these data structures based on
the CPU would create naming challenges when this scenario arrives, no?

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

Why not use the guid as part of the naming to make clear that CPU model
does not dictate the layout?


> 
> 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