linux-kernel - RE: [PATCH 2/2] x86/resctrl: Don't workqueue local event counter reads

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Message-ID: <SJ1PR11MB608302AB52A300B9C21E4AA9FC532@SJ1PR11MB6083.namprd11.prod.outlook.com>
Date: Wed, 6 Nov 2024 17:12:38 +0000
From: "Luck, Tony" <tony.luck@...el.com>
To: Peter Newman <peternewman@...gle.com>, "Chatre, Reinette"
	<reinette.chatre@...el.com>
CC: "Yu, Fenghua" <fenghua.yu@...el.com>, Thomas Gleixner
	<tglx@...utronix.de>, Ingo Molnar <mingo@...hat.com>, Borislav Petkov
	<bp@...en8.de>, Dave Hansen <dave.hansen@...ux.intel.com>, "x86@...nel.org"
	<x86@...nel.org>, "H . Peter Anvin" <hpa@...or.com>, Babu Moger
	<babu.moger@....com>, James Morse <james.morse@....com>, Martin Kletzander
	<nert.pinx@...il.com>, Shaopeng Tan <tan.shaopeng@...itsu.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>, "Eranian,
 Stephane" <eranian@...gle.com>
Subject: RE: [PATCH 2/2] x86/resctrl: Don't workqueue local event counter
 reads

> As a refresher, the original issue that led to this situation was how
> an MPAM CSU (cache occupancy) monitor can be installed in response to
> a read request. The number of monitors is usually small (or just 1),
> so they need to be frequently installed, there can be access issues
> depending on what CPU wants to read which domain, and installing a
> monitor is a slow operation that requires waiting.

Maybe the ARM implementation should adopt a similar approach to
Babu's ABMC patches and provide an explicit mechanism to bind a
h/w counter to an instance of a monitor event. Binding on demand
when a user reads an event file seems awkward for users. Especially
of the number of counters is >1, but unknown.

-Tony