linux-kernel - Re: [PATCH v15 11/32] x86,fs/resctrl: Handle events that can be read from any CPU

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Message-ID: <34dfe97d-3aa0-4fc5-8f1d-3da5066a0b6c@intel.com>
Date: Tue, 9 Dec 2025 11:39:56 -0800
From: Reinette Chatre <reinette.chatre@...el.com>
To: Tony Luck <tony.luck@...el.com>, 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>, Chen Yu <yu.c.chen@...el.com>
CC: <x86@...nel.org>, <linux-kernel@...r.kernel.org>,
	<patches@...ts.linux.dev>
Subject: Re: [PATCH v15 11/32] x86,fs/resctrl: Handle events that can be read
 from any CPU

Hi Tony,

On 12/4/25 12:53 PM, Tony Luck wrote:
> resctrl assumes that monitor events can only be read from a CPU in the
> cpumask_t set of each domain.  This is true for x86 events accessed with an
> MSR interface, but may not be true for other access methods such as MMIO.
> 
> Introduce and use flag mon_evt::any_cpu, settable by architecture, that
> indicates there are no restrictions on which CPU can read that event.

I propose to append (something like): "This flag is not supported by the L3
event reading that requires to be run on a CPU that belongs to the L3
domain of the event being read."

> diff --git a/fs/resctrl/monitor.c b/fs/resctrl/monitor.c
> index 340b847ab397..081ff659b52c 100644
> --- a/fs/resctrl/monitor.c
> +++ b/fs/resctrl/monitor.c
> @@ -518,10 +518,12 @@ static int __mon_event_count(struct rdtgroup *rdtgrp, struct rmid_read *rr)
>  {
>  	switch (rr->r->rid) {
>  	case RDT_RESOURCE_L3:
> -		if (rr->hdr)
> +		if (rr->hdr) {
> +			WARN_ON_ONCE(rr->evt->any_cpu);

I appreciate that this addresses the feedback from v13 but it needs to be adjusted for the
code changes made since then. This means that this warning applies to both
__l3_mon_event_count() and __l3_mon_event_count_sum() , no?

>  			return __l3_mon_event_count(rdtgrp, rr);
> -		else
> +		} else {
>  			return __l3_mon_event_count_sum(rdtgrp, rr);
> +		}
>  	default:
>  		rr->err = -EINVAL;
>  		return -EINVAL;

Reinette