linux-kernel - Re: [PATCH v2 8/8] arch_topology: Add support to build llc

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Date:   Thu, 19 May 2022 13:10:51 -0500
From:   Rob Herring <robh+dt@...nel.org>
To:     Sudeep Holla <sudeep.holla@....com>
Cc:     Atish Patra <atishp@...shpatra.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Atish Patra <atishp@...osinc.com>,
        Vincent Guittot <vincent.guittot@...aro.org>,
        Morten Rasmussen <morten.rasmussen@....com>,
        Dietmar Eggemann <dietmar.eggemann@....com>,
        Qing Wang <wangqing@...o.com>,
        linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>,
        linux-riscv <linux-riscv@...ts.infradead.org>
Subject: Re: [PATCH v2 8/8] arch_topology: Add support to build llc_sibling on
 DT platforms

On Wed, May 18, 2022 at 4:34 AM Sudeep Holla <sudeep.holla@....com> wrote:
>
> ACPI PPTT provides cache identifiers and especially the last level cache
> identifier is used in obtaining last level cache siblings amongst CPUs.
>
> While we have the cpu map representing all the CPUs sharing last level
> cache in the cacheinfo driver, it is populated quite late in the boot
> while the information is needed to build scheduler domains quite early.

Late is because it's a device_initcall() rather than late in the cpu
hotplug state machine, right? The late aspect is for sysfs presumably,
but I think we could decouple that. Do all the firmware cache parsing
early and then populate the sysfs parts later. It's not a unique
problem as the DT unflattening and init code has to do the same thing.
I'd assume the hotplug and cpu sysfs devices have to deal with the
same thing.

Rob