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

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Date: Thu, 27 Jun 2024 08:22:11 -0700
From: Ricardo Neri <ricardo.neri-calderon@...ux.intel.com>
To: Brice Goglin <brice.goglin@...il.com>
Cc: 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,
	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>,
	"Liang, Kan" <kan.liang@...ux.intel.com>,
	Andrew Cooper <andrew.cooper3@...rix.com>
Subject: Re: [PATCH 0/9] Add CPU-type to topology

On Wed, Jun 19, 2024 at 11:22:16PM +0200, Brice Goglin wrote:

[...]

> > There can be many ways to expose this information in sysfs. Like this ...
> > 
> > > [1] https://lkml.org/lkml/2020/10/2/1208
> > ... exposes /sys/devices/system/cpu/types which, in hybrid parts, creates a
> > subdirectory for each type of CPU. Each subdirectory contains a CPU list
> > and a CPU map that user space can query.
> > 
> > The other way is to expose the CPU-type in a file:
> > 
> > 	/sys/devices/system/cpu/cpuN/type
> > 
> > that could return the CPU-type of the CPU N. Is there a preference?
> 
> 
> I'd vote for the former.

+1. With the former you can read all CPUs of a given type in one go whereas
with the latter you have to iterate over all CPUs. By the time you are done
CPUs may have gone offline or online.