Message-ID: <c65961d2-d31b-4ff9-ac1c-b5e3c06a46ba@igalia.com>
Date: Mon, 15 Dec 2025 10:57:03 +0900
From: Changwoo Min <changwoo@...lia.com>
To: Andrew Lunn <andrew@...n.ch>
Cc: 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

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. 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.


> Naming is important, and causes a lot of pain when you get it
> wrong. Linux has PHYs and generic PHYs. The PHY subsystem has been
> around a long time, and generic PHY is much newer. And sometimes a PHY
> has a generic PHY associated to it, so it can get really confusing
> unless you are very precises with wording.
> 
> We need to be careful with any generic term, such as energy model.
> 

I absolutely agree with you. Thank you for sharing your concerns and
examples.

Regards,
Changwoo Min

> 	Andrew
> 

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