linux-kernel - Re: [PATCH v4 1/2] dt-bindings: cpufreq: add virtual cpufreq device

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Message-ID: <CAGETcx9-n0z5buWgtLZ+6VxW2jEko1GWzkGtGhFiZEq-x_G4nw@mail.gmail.com>
Date:   Thu, 7 Dec 2023 14:44:36 -0800
From:   Saravana Kannan <saravanak@...gle.com>
To:     Marc Zyngier <maz@...nel.org>
Cc:     David Dai <davidai@...gle.com>,
        "Rafael J. Wysocki" <rafael@...nel.org>,
        Viresh Kumar <viresh.kumar@...aro.org>,
        Rob Herring <robh+dt@...nel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
        Conor Dooley <conor+dt@...nel.org>,
        Sudeep Holla <sudeep.holla@....com>,
        Quentin Perret <qperret@...gle.com>,
        Masami Hiramatsu <mhiramat@...gle.com>,
        Will Deacon <will@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Vincent Guittot <vincent.guittot@...aro.org>,
        Oliver Upton <oliver.upton@...ux.dev>,
        Dietmar Eggemann <dietmar.eggemann@....com>,
        Pavan Kondeti <quic_pkondeti@...cinc.com>,
        Gupta Pankaj <pankaj.gupta@....com>,
        Mel Gorman <mgorman@...e.de>, kernel-team@...roid.com,
        linux-pm@...r.kernel.org, devicetree@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v4 1/2] dt-bindings: cpufreq: add virtual cpufreq device

On Wed, Nov 15, 2023 at 12:49 AM Marc Zyngier <maz@...nel.org> wrote:
>
> On Sat, 11 Nov 2023 01:49:29 +0000,
> David Dai <davidai@...gle.com> wrote:
> >
> > Adding bindings to represent a virtual cpufreq device.
> >
> > Virtual machines may expose MMIO regions for a virtual cpufreq device
> > for guests to read frequency information or to request frequency
> > selection. The virtual cpufreq device has an individual controller for
> > each frequency domain.
>
> I would really refrain form having absolute frequencies here. A
> virtual machine can be migrated, and there are *zero* guarantees that
> the target system has the same clock range as the source.
>
> This really should be a relative number, much like the capacity. That,
> at least, can be migrated across systems.

There's nothing in this patch that mandates absolute frequency.
In true KVM philosophy, we leave it to the VMM to decide.

-Saravana