linux-kernel - Re: [PATCH v8 13/13] arm64: topology: divorce MC scheduling domain from core

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Message-ID: <20180503151255.GB28409@work-enc>
Date:   Thu, 3 May 2018 16:12:55 +0100
From:   Morten Rasmussen <morten.rasmussen@....com>
To:     Jeremy Linton <jeremy.linton@....com>
Cc:     linux-acpi@...r.kernel.org, Sudeep.Holla@....com,
        linux-arm-kernel@...ts.infradead.org, Lorenzo.Pieralisi@....com,
        hanjun.guo@...aro.org, rjw@...ysocki.net, Will.Deacon@....com,
        Catalin.Marinas@....com, gregkh@...uxfoundation.org,
        Mark.Rutland@....com, linux-kernel@...r.kernel.org,
        linux-riscv@...ts.infradead.org, wangxiongfeng2@...wei.com,
        vkilari@...eaurora.org, ahs3@...hat.com, Dietmar.Eggemann@....com,
        palmer@...ive.com, lenb@...nel.org, john.garry@...wei.com,
        austinwc@...eaurora.org, tnowicki@...iumnetworks.com,
        jhugo@....qualcomm.com, timur@....qualcomm.com,
        ard.biesheuvel@...aro.org
Subject: Re: [PATCH v8 13/13] arm64: topology: divorce MC scheduling domain
 from core_siblings

On Wed, Apr 25, 2018 at 06:31:21PM -0500, Jeremy Linton wrote:
> Now that we have an accurate view of the physical topology
> we need to represent it correctly to the scheduler. Generally MC
> should equal the LLC in the system, but there are a number of
> special cases that need to be dealt with.
> 
> In the case of NUMA in socket, we need to assure that the sched
> domain we build for the MC layer isn't larger than the DIE above it.
> Similarly for LLC's that might exist in cross socket interconnect or
> directory hardware we need to assure that MC is shrunk to the socket
> or NUMA node.
> 
> This patch builds a sibling mask for the LLC, and then picks the
> smallest of LLC, socket siblings, or NUMA node siblings, which
> gives us the behavior described above. This is ever so slightly
> different than the similar alternative where we look for a cache
> layer less than or equal to the socket/NUMA siblings.
> 
> The logic to pick the MC layer affects all arm64 machines, but
> only changes the behavior for DT/MPIDR systems if the NUMA domain
> is smaller than the core siblings (generally set to the cluster).
> Potentially this fixes a possible bug in DT systems, but really
> it only affects ACPI systems where the core siblings is correctly
> set to the socket siblings. Thus all currently available ACPI
> systems should have MC equal to LLC, including the NUMA in socket
> machines where the LLC is partitioned between the NUMA nodes.
> 
> Signed-off-by: Jeremy Linton <jeremy.linton@....com>

This patch looks good to me.

Acked-by: Morten Rasmussen <morten.rasmussen@....com>