linux-kernel - Re: [PATCH v7 13/13] arm64: topology: divorce MC scheduling domain from core

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Date:   Thu, 8 Mar 2018 21:41:17 +0100
From:   Brice Goglin <brice.goglin@...il.com>
To:     Morten Rasmussen <morten.rasmussen@....com>,
        Jeremy Linton <jeremy.linton@....com>
Cc:     mark.rutland@....com, vkilari@...eaurora.org,
        lorenzo.pieralisi@....com, catalin.marinas@....com,
        tnowicki@...iumnetworks.com, gregkh@...uxfoundation.org,
        will.deacon@....com, dietmar.eggemann@....com, rjw@...ysocki.net,
        linux-kernel@...r.kernel.org, ahs3@...hat.com,
        linux-acpi@...r.kernel.org, palmer@...ive.com,
        hanjun.guo@...aro.org, sudeep.holla@....com,
        austinwc@...eaurora.org, linux-riscv@...ts.infradead.org,
        john.garry@...wei.com, wangxiongfeng2@...wei.com,
        linux-arm-kernel@...ts.infradead.org, lenb@...nel.org
Subject: Re: [PATCH v7 13/13] arm64: topology: divorce MC scheduling domain
 from core_siblings


> Is there a good reason for diverging instead of adjusting the
> core_sibling mask? On x86 the core_siblings mask is defined by the last
> level cache span so they don't have this issue. 

No. core_siblings is defined as the list of cores that have the same
physical_package_id (see the doc of sysfs topology files), and LLC can
be smaller than that.
Example with E5v3 with cluster-on-die (two L3 per package, core_siblings
is twice larger than L3 cpumap):
https://www.open-mpi.org/projects/hwloc/lstopo/images/2XeonE5v3.v1.11.png
On AMD EPYC, you even have up to 8 LLC per package.

Brice