linux-kernel - RE: [PATCH] x86, sched: Allow NUMA nodes to share an LLC on Intel platforms

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Date:   Tue, 9 Feb 2021 23:09:27 +0000
From:   "Luck, Tony" <tony.luck@...el.com>
To:     "Schofield, Alison" <alison.schofield@...el.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...nel.org>, Borislav Petkov <bp@...en8.de>
CC:     "x86@...nel.org" <x86@...nel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Tim Chen <tim.c.chen@...ux.intel.com>,
        "H. Peter Anvin" <hpa@...ux.intel.com>,
        Peter Zijlstra <peterz@...radead.org>,
        David Rientjes <rientjes@...gle.com>,
        Igor Mammedov <imammedo@...hat.com>,
        Prarit Bhargava <prarit@...hat.com>,
        "brice.goglin@...il.com" <brice.goglin@...il.com>
Subject: RE: [PATCH] x86, sched: Allow NUMA nodes to share an LLC on Intel
 platforms

> +#define X86_BUG_NUMA_SHARES_LLC		X86_BUG(25) /* CPU may enumerate an LLC shared by multiple NUMA nodes */

During internal review I wondered why this is a "BUG" rather than a "FEATURE" bit.

Apparently, the suggestion for "BUG" came from earlier community discussions.

Historically it may have seemed reasonable to say that a cache cannot span
NUMA domains. But with more and more things moving off the motherboard
and into the socket, this doesn't seem too weird now.

-Tony