linux-kernel - Re: [PATCH v8 0/8] Add support for Sub-NUMA cluster (SNC) systems

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Message-ID: <94a38b28-5af9-4280-1323-7c43d934ee37@intel.com>
Date:   Tue, 3 Oct 2023 14:44:18 -0700
From:   Reinette Chatre <reinette.chatre@...el.com>
To:     Tony Luck <tony.luck@...el.com>, Fenghua Yu <fenghua.yu@...el.com>,
        "Peter Newman" <peternewman@...gle.com>,
        Jonathan Corbet <corbet@....net>,
        Shuah Khan <skhan@...uxfoundation.org>, <x86@...nel.org>
CC:     Shaopeng Tan <tan.shaopeng@...itsu.com>,
        James Morse <james.morse@....com>,
        Jamie Iles <quic_jiles@...cinc.com>,
        Babu Moger <babu.moger@....com>,
        Randy Dunlap <rdunlap@...radead.org>,
        <linux-kernel@...r.kernel.org>, <linux-doc@...r.kernel.org>,
        <patches@...ts.linux.dev>
Subject: Re: [PATCH v8 0/8] Add support for Sub-NUMA cluster (SNC) systems

Tony,

On 10/3/2023 2:30 PM, Tony Luck wrote:
> The Sub-NUMA cluster feature on some Intel processors partitions
> the CPUs that share an L3 cache into two or more sets. This plays
> havoc with the Resource Director Technology (RDT) monitoring features.
> Prior to this patch Intel has advised that SNC and RDT are incompatible.
> 
> Some of these CPU support an MSR that can partition the RMID
> counters in the same way. This allows for monitoring features
> to be used (with the caveat that memory accesses between different
> SNC NUMA nodes may still not be counted accurately.

Almost. For reference:
https://lore.kernel.org/lkml/e350514e-76ed-14ea-3e74-c0852658182f@intel.com/

No need to send a new series just for this, but this series does find
itself at the back of my queue.

> Note that this patch series improves resctrl reporting considerably
> on systems with SNC enabled, but there will still be some anomalies
> for processes accessing memory from other sub-NUMA nodes.
> 
> Signed-off-by: Tony Luck <tony.luck@...el.com>

Reinette