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

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Message-ID: <SJ1PR11MB6083D1B48E48BBE797ACF21FFC522@SJ1PR11MB6083.namprd11.prod.outlook.com>
Date: Tue, 5 Nov 2024 23:39:23 +0000
From: "Luck, Tony" <tony.luck@...el.com>
To: "Chatre, Reinette" <reinette.chatre@...el.com>, Peter Newman
	<peternewman@...gle.com>, "Yu, Fenghua" <fenghua.yu@...el.com>
CC: 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

> I think this change already undoes the motivation for 09909e098113
> ("x86/resctrl: Queue mon_event_read() instead of sending an IPI")? As you mention in
> changelog the goal of that work was to enable resctrl_arch_rmid_read() to sleep.
> This change will call resctrl_arch_rmid_read() with preemption disabled if
> it happens to be called on CPU in monitoring domain. Would that not cause
> MPAM monitor count reads from CPU in domain to be a bug?
>
> Could you please try out this patch with CONFIG_DEBUG_ATOMIC_SLEEP=y?

How is this all going to look after the split into fs/resctrl and arch/* ?

Is the file system code going to have implementation choices that prevent
performance sensitive users like Peter from optimizing monitor event
reads by binding the monitor process to a CPU in the right domain
to avoid IPI?

-Tony