linux-kernel - Re: [PATCH 0/9] Add CPU-type to topology

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Message-ID: <8d757ea3-87a3-4663-ac76-66b04e33e6b3@gmail.com>
Date: Tue, 18 Jun 2024 14:49:10 +0200
From: Brice Goglin <brice.goglin@...il.com>
To: Pawan Gupta <pawan.kumar.gupta@...ux.intel.com>,
 Thomas Gleixner <tglx@...utronix.de>, Ingo Molnar <mingo@...hat.com>,
 Borislav Petkov <bp@...en8.de>, Dave Hansen <dave.hansen@...ux.intel.com>,
 x86@...nel.org
Cc: daniel.sneddon@...ux.intel.com, tony.luck@...el.com,
 linux-kernel@...r.kernel.org, linux-pm@...r.kernel.org,
 linux-perf-users@...r.kernel.org, Josh Poimboeuf <jpoimboe@...nel.org>,
 Srinivas Pandruvada <srinivas.pandruvada@...ux.intel.com>,
 "Rafael J. Wysocki" <rafael@...nel.org>,
 Ricardo Neri <ricardo.neri-calderon@...ux.intel.com>,
 "Liang, Kan" <kan.liang@...ux.intel.com>,
 Andrew Cooper <andrew.cooper3@...rix.com>
Subject: Re: [PATCH 0/9] Add CPU-type to topology

Le 17/06/2024 à 11:11, Pawan Gupta a écrit :
> Hi,
>
> This series adds support for CPU-type (CPUID.1A.EAX[31-24] on Intel) to
> differentiate between hybrid variants P+E, P-only, E-only that share the
> same Family/Model/Stepping. One of the use case for CPU-type is the
> affected CPU table for CPU vulnerabilities, which can now use the CPU-type
> to filter the unaffected variants.
>
> * Patch 1 adds cpu-type to CPU topology structure and introduces
>    topology_cpu_type() to get the CPU-type.
>
> * Patch 2-4 replaces usages of get_this_hybrid_cpu_type() with
>    topology_cpu_type().
>
> * Patch 5-7 Updates CPU-matching infrastructure to use CPU-type.
>
> * Patch 8 cleans up the affected CPU list.
>
> * Patch 9 uses the CPU-type to exclude P-only parts from the RFDS affected
>    list.

Hello

Is there still a plan to expose this info in sysfs? Userspace currently 
uses frequencies to guess which cores are E or P. Intel sent some 
patches several years ago [1], but they got abandoned nowhere as far as 
I know. There was also some discussion about using a "capacity" field 
like ARM does, but IIRC Intel didn't like the idea in the end.

Thanks

Brice

[1] https://lkml.org/lkml/2020/10/2/1208