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

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Message-ID: <f947c0f5-e94d-4aea-9e06-687b6f7eeae1@gmail.com>
Date: Sat, 29 Jun 2024 13:37:35 +0200
From: Brice Goglin <brice.goglin@...il.com>
To: Pawan Gupta <pawan.kumar.gupta@...ux.intel.com>,
 Ricardo Neri <ricardo.neri-calderon@...ux.intel.com>
Cc: Dave Hansen <dave.hansen@...el.com>,
 srinivas pandruvada <srinivas.pandruvada@...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, 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>,
 "Rafael J. Wysocki" <rafael@...nel.org>,
 "Liang, Kan" <kan.liang@...ux.intel.com>,
 Andrew Cooper <andrew.cooper3@...rix.com>
Subject: Re: [PATCH 0/9] Add CPU-type to topology

Le 27/06/2024 à 15:22, Pawan Gupta a écrit :
> On Thu, Jun 27, 2024 at 05:51:54AM -0700, Ricardo Neri wrote:
>> ARM gives userspace specific details. This makes more sense to me. Instead
>> of reading these details, user space would have to infer these details if
>> a CPU type was given in sysfs.
>>
>> Having said that, Intel does have a CPUID leaf that gives the CPU type. Such
>> leaf also has a "Native Model ID". Exposing only the CPU type may not be
>> sufficient.
> Do we know if there are applications that would benefit from this information?

There are HPC users who want a homogeneous set of cores, ie only P-core, 
or only E-core without the low power ones (because they don't want some 
imbalance between task speed in homogeneous parallel jobs). I've 
received requests from hwloc users running small parallel jobs on their 
desktop/laptop machines, and also from developers of big apps who want 
to debug on their laptop without heterogeneous cores creating imbalance 
that don't exist on servers.

They don't care much about the actual hardware details so far, they 
mostly want an ordered list of set of homogeneous cores (ordered from 
performance -> low-energy).

Brice