linux-kernel - Re: [PATCH] arm64: defconfig: enable CONFIG_SCHED

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Message-ID: <c45b13b9-52ae-a52b-ce39-77f7ebe09507@gentwo.org>
Date: Wed, 13 Aug 2025 15:56:47 -0700 (PDT)
From: "Christoph Lameter (Ampere)" <cl@...two.org>
To: Sudeep Holla <sudeep.holla@....com>
cc: Jeremy Linton <jeremy.linton@....com>, 
    Huang Shijie <shijie@...amperecomputing.com>, catalin.marinas@....com, 
    will@...nel.org, patches@...erecomputing.com, 
    Shubhang@...amperecomputing.com, krzysztof.kozlowski@...aro.org, 
    bjorn.andersson@....qualcomm.com, geert+renesas@...der.be, arnd@...db.de, 
    nm@...com, ebiggers@...nel.org, nfraprado@...labora.com, 
    prabhakar.mahadev-lad.rj@...renesas.com, 
    linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] arm64: defconfig: enable CONFIG_SCHED_CLUSTER

On Wed, 13 Aug 2025, Christoph Lameter (Ampere) wrote:

> Can we figure out which platforms benchmarks were affected and why?
>
> It seems the notion of a "cluster" on ARM64 is derived (I guess a better
> word than "invented" hehe)  from sibling information instead of PPTT. But
> using that information should work fine right?

Sorry no that is not correct. The cluster information is correctly read
from the ACPI tables and the cluster ids are avaialble in

	/sys/devices/system/cpu/cpuXX/topology/cluster_id

if CONFIG_SCHED_CLUSTER is enabled.

If there is an issue then it is a problem with the vendor firmware
providing cluster id configurations via ACPI that cause regressions.

We could add a blacklist for those platforms to avoid regressions but we
should not allow that to hinder us to enable full support for clustering
on ARM64.