linux-kernel - Re: [PATCH v21 16/18] x86/resctrl: Enable shared RMID mode on Sub-NUMA Cluster (SNC) systems

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Message-ID: <23d982d2-97c5-4f2f-a034-858bec34bef7@intel.com>
Date: Tue, 25 Jun 2024 16:35:17 -0700
From: Reinette Chatre <reinette.chatre@...el.com>
To: Tony Luck <tony.luck@...el.com>, Fenghua Yu <fenghua.yu@...el.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>
CC: <x86@...nel.org>, <linux-kernel@...r.kernel.org>,
	<patches@...ts.linux.dev>
Subject: Re: [PATCH v21 16/18] x86/resctrl: Enable shared RMID mode on
 Sub-NUMA Cluster (SNC) systems

Hi Tony,

On 6/21/24 3:38 PM, Tony Luck wrote:
> Hardware has two RMID configuration options for SNC systems. The default
> mode divides RMID counters between SNC nodes. E.g. with 200 RMIDs and
> two SNC nodes per L3 cache RMIDs 0..99 are used on node 0, and 100..199
> on node 1. This isn't compatible with Linux resctrl usage. On this
> example system a process using RMID 5 would only update monitor counters
> while running on SNC node 0.
> 
> The other mode is "RMID Sharing Mode". This is enabled by clearing bit
> 0 of the RMID_SNC_CONFIG (0xCA0) model specific register. In this mode
> the number of logical RMIDs is the number of physical RMIDs (from CPUID
> leaf 0xF) divided by the number of SNC nodes per L3 cache instance. A
> process can use the same RMID across different SNC nodes.
> 
> See the "Intel Resource Director Technology Architecture Specification"
> for additional details.
> 
> When SNC is enabled, update the MSR when a monitor domain is marked
> online. Technically this is overkill. It only needs to be done once
> per L3 cache instance rather than per SNC domain. But there is no harm
> in doing it more than once, and this is not in a critical path.
> 
> Signed-off-by: Tony Luck <tony.luck@...el.com>
> ---

Reviewed-by: Reinette Chatre <reinette.chatre@...el.com>

Reinette