linux-kernel - Re: [PATCH 0/7] x86/topology: Improve CPUID.1F handling

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Message-ID: <YveAp8W3zZliQXrq@gmail.com>
Date:   Sat, 13 Aug 2022 12:44:55 +0200
From:   Ingo Molnar <mingo@...nel.org>
To:     Zhang Rui <rui.zhang@...el.com>
Cc:     linux-kernel@...r.kernel.org, x86@...nel.org,
        linux-hwmon@...r.kernel.org, tglx@...utronix.de, mingo@...hat.com,
        bp@...en8.de, dave.hansen@...ux.intel.com, hpa@...or.com,
        corbet@....net, fenghua.yu@...el.com, jdelvare@...e.com,
        linux@...ck-us.net, len.brown@...el.com
Subject: Re: [PATCH 0/7] x86/topology: Improve CPUID.1F handling


* Zhang Rui <rui.zhang@...el.com> wrote:

> On Intel AlderLake-N platforms where there are Ecores only, the Ecore
> Module topology is enumerated via CPUID.1F Module level, which has not
> been supported by Linux kernel yet.
> 
> This exposes two issues in current CPUID.1F handling code.
> 1. Linux interprets the Module id bits as package id and erroneously
>    reports a multi module system as a multi-package system.
> 2. Linux excludes the unknown Module id bits from the core_id, and results
>    in duplicate core_id’s shown in a package after the first issue solved.
> 
> Plus that, a third problem is observed on Intel Hybrid ADL-S/P platforms.
> The return value of CPUID.1F SMT level EBX (number of siblings) differs on
> Pcore CPUs and Ecore CPUs, and results in inconsistent smp_num_siblings
> value based on the Pcore/Ecore CPU enumeration order. This could bring
> some potential issues although we have not observed any functionalities
> issues so far.
> 
> Patch 1/7 and 2/7 fix the first two issues. And at the same time, it
> reveals a reality that the core_id could be sparse on platforms with
> CPUID.1F support.
> Patch 3/7 improves coretemp driver code to be able to handle sparse core
> id, which is the only driver that uses core_id as array index and run on
> platforms with CPUID.1F support.
> 
> Patch 4/7 to 7/7 propose a fix for the third problem and update the
> related Documents.

Yeah, so patch 3/7 probably needs to come first - otherwise there's a 
window for bisection breakage.

Thanks,

	Ingo