Message-ID: <CAJZ5v0iX39rvdaoha18N-rpKLinGZ1cjTb1rV1Azh0Y7kYdaJQ@mail.gmail.com>
Date: Mon, 15 Dec 2025 11:30:41 +0100
From: "Rafael J. Wysocki" <rafael@...nel.org>
To: Changwoo Min <changwoo@...lia.com>
Cc: Andrew Lunn <andrew@...n.ch>, Donald Hunter <donald.hunter@...il.com>, 
	Lukasz Luba <lukasz.luba@....com>, linux-pm@...r.kernel.org, sched-ext@...ts.linux.dev, 
	Jakub Kicinski <kuba@...nel.org>, Network Development <netdev@...r.kernel.org>, 
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: Concerns with em.yaml YNL spec

On Mon, Dec 15, 2025 at 2:57 AM Changwoo Min <changwoo@...lia.com> wrote:
>
> Hi  Andrew,
>
> On 12/15/25 01:21, Andrew Lunn wrote:
> >>> We also need to watch out for other meaning of these letters. In the
> >>> context of networking and Power over Ethernet, PD means Powered
> >>> Device. We generally don't need to enumerate the PD, we are more
> >>> interested in the Power Sourcing Equipment, PSE.
> >>>
> >>> And a dumb question. What is an energy model? A PSE needs some level
> >>> of energy model, it needs to know how much energy each PD can consume
> >>> in order that it is not oversubscribed.Is the energy model generic
> >>> enough that it could be used for this? Or should this energy model get
> >>> a prefix to limit its scope to a performance domain? The suggested
> >>> name of this file would then become something like
> >>> performance-domain-energy-model.yml?
> >>>
> >>
> >> Lukasz might be the right person for this question. In my view, the
> >> energy model essentially provides the performance-versus-power-
> >> consumption curve for each performance domain.
> >
> > The problem here is, you are too narrowly focused. My introduction
> > said:
> >
> >>> In the context of networking and Power over Ethernet, PD means
> >>> Powered Device.
> >
> > You have not given any context. Reading the rest of your email, it
> > sounds like you are talking about the energy model/performance domain
> > for a collection of CPU cores?
> >
> > Now think about Linux as a whole, not the little corner you are
> > interested in. Are there energy models anywhere else in Linux? What
> > about the GPU cores? What about Linux regulators controlling power to
> > peripherals? I pointed out the use case of Power over Ethernet needing
> > an energy model.
> >
> >> Conceptually, the energy model covers the system-wide information; a
> >> performance domain is information about one domain (e.g., big/medium/
> >> little CPU blocks), so it is under the energy model; a performance state
> >> is one dot in the performance-versus-power-consumption curve of a
> >> performance domain.
> >>
> >> Since the energy model covers the system-wide information, energy-
> >> model.yaml (as Donald suggested) sounds better to me.
> >
> > By system-wide, do you mean the whole of Linux? I could use it for
> > GPUs, regulators, PoE? Is it sufficiently generic? I somehow doubt it
> > is. So i think you need some sort of prefix to indicate the domain it
> > is applicable to. We can then add GPU energy models, PoE energy
> > models, etc by the side without getting into naming issues.
> >
>
> This is really the question for the energy model maintainers. In my
> understanding, the energy model can cover any device in the system,
> including GPUs.

That's correct.

> But, in my limited experience, I haven’t seen such cases beyond CPUs.
>
> @Lukasz — What do you think? The focus here is on the scope of the
> “energy model” and its proper naming in the NETLINK.

I think you need to frame your question more specifically.

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