linux-kernel - Re: [PATCH v3] x86, sched: Treat Intel SNC topology as default, COD as exception

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Message-ID: <YHhBaDLjBOZUKCrW@hirez.programming.kicks-ass.net>
Date:   Thu, 15 Apr 2021 15:36:40 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Alison Schofield <alison.schofield@...el.com>
Cc:     Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...nel.org>, Borislav Petkov <bp@...en8.de>,
        x86@...nel.org, linux-kernel@...r.kernel.org,
        stable@...r.kernel.org, Dave Hansen <dave.hansen@...ux.intel.com>,
        Tony Luck <tony.luck@...el.com>,
        Tim Chen <tim.c.chen@...ux.intel.com>,
        "H. Peter Anvin" <hpa@...ux.intel.com>,
        David Rientjes <rientjes@...gle.com>,
        Igor Mammedov <imammedo@...hat.com>,
        Prarit Bhargava <prarit@...hat.com>, brice.goglin@...il.com
Subject: Re: [PATCH v3] x86, sched: Treat Intel SNC topology as default, COD
 as exception

On Wed, Mar 10, 2021 at 11:02:33AM -0800, Alison Schofield wrote:
> Commit 1340ccfa9a9a ("x86,sched: Allow topologies where NUMA nodes
> share an LLC") added a vendor and model specific check to never
> call topology_sane() for Intel Skylake Server systems where NUMA
> nodes share an LLC.
> 
> Intel Ice Lake and Sapphire Rapids CPUs also enumerate an LLC that is
> shared by multiple NUMA nodes. The LLC on these CPUs is shared for
> off-package data access but private to the NUMA node for on-package
> access. Rather than managing a list of allowable SNC topologies, make
> this SNC topology the default, and treat Intel's Cluster-On-Die (COD)
> topology as the exception.
> 
> In SNC mode, Sky Lake, Ice Lake, and Sapphire Rapids servers do not
> emit this warning:
> 
> sched: CPU #3's llc-sibling CPU #0 is not on the same node! [node: 1 != 0]. Ignoring dependency.
> 
> Acked-by: Dave Hansen <dave.hansen@...ux.intel.com>
> Suggested-by: Peter Zijlstra (Intel) <peterz@...radead.org>
> Signed-off-by: Alison Schofield <alison.schofield@...el.com>

Seeing how this is basically what I gave you earlier; but now tested and
with comments on,

Acked-by: Peter Zijlstra (Intel) <peterz@...radead.org>

Boris, will you make it happen, or you want me to queue it somewhere
x86/core like?