linux-kernel - RE: [PATCH v11 17/31] x86/resctrl: Find and enable usable telemetry events

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Message-ID: <SJ1PR11MB6083F8C67C6C8C5DBFF3832AFCE3A@SJ1PR11MB6083.namprd11.prod.outlook.com>
Date: Mon, 6 Oct 2025 21:54:04 +0000
From: "Luck, Tony" <tony.luck@...el.com>
To: "Chatre, Reinette" <reinette.chatre@...el.com>
CC: Fenghua Yu <fenghuay@...dia.com>, "Wieczor-Retman, Maciej"
	<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>, "Chen,
 Yu C" <yu.c.chen@...el.com>, "x86@...nel.org" <x86@...nel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"patches@...ts.linux.dev" <patches@...ts.linux.dev>
Subject: RE: [PATCH v11 17/31] x86/resctrl: Find and enable usable telemetry
 events

> > I don't feel that it would be worthwhile to suppress creation of these files for
> > a "can't happen" situation. I'm not sure that doing so would be significantly
> > better from a user interface perspective. Users would get slightly more notice
> > (-ENOENT when trying to open the file). But the code would require
> > architecture calls from file system code to check which files need to be created
> > separately for each domain.
>
> I think it is sufficient to document this in the commit message to help create
> confidence in robustness in support of different scenarios. I have not encountered such
> a system but could this scenario be similar to one where a two socket system supports MBM
> but only one socket has memory populated? I do not know what reading the counter MSR will
> return in this case though.

The counting h/w is likely unaware of whether DIMMs slots are populated or not. My guess
would be that in this case the counters would read as zero forever, rather than "unavailable".

CXL supports hot-add memory. So whether a node has memory could change at runtime
on a system with CXL support.

-Tony