linux-kernel - Re: [PATCH v2] PM: EM: Add inotify support when the energy model is updated.

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Message-ID: <c85cbb96-8c0f-4f91-a568-20c9de65b10b@igalia.com>
Date: Thu, 22 May 2025 17:35:55 +0900
From: Changwoo Min <changwoo@...lia.com>
To: Lukasz Luba <lukasz.luba@....com>
Cc: christian.loehle@....com, tj@...nel.org, pavel@...nel.org,
 kernel-dev@...lia.com, linux-pm@...r.kernel.org,
 linux-kernel@...r.kernel.org, len.brown@...el.com,
 "Rafael J. Wysocki" <rafael@...nel.org>
Subject: Re: [PATCH v2] PM: EM: Add inotify support when the energy model is
 updated.



On 5/22/25 17:19, Lukasz Luba wrote:
> 
> 
> On 5/10/25 12:34, Rafael J. Wysocki wrote:
>> On Sat, May 10, 2025 at 7:07 AM Changwoo Min <changwoo@...lia.com> wrote:

>>> I am curious about whether the energy mode is likely to be updated more
>>> often with this change. How often the energy model is likely to be
>>> updated is the factor to be considered for the interface and the model
>>> to post-processing the eneergy model (in the BPF schedulers).
>>
>> It really is hard to say precisely because eventually this will depend
>> on the platform firmware.  Hopefully, this is not going to happen too
>> often, but if the thermal envelope of the platform is tight, for
>> instance, it may not be the case.
> 
> It's hard to say for all use cases, but there are some easy to measure
> and understand:
> 
> 1. Long scenarios with heavy GPU usage (e.g. gaming). Power on CPUs
>     built from High-Performance cells can be affected by +20% and after
>     ~1min
> 2. Longer recording with heavy ISP usage, similar to above
> 
> In those two, it's sufficient to update the EM every 1-3sec to reach
> this +20% after 60sec. Although, at the beginning when the GPU starts
> heating the updates should happen a bit more often.
> 
> There are some more complex cases, e.g. when more than 1 Big CPU does
> heavy computations and the heat is higher than normal EM model of
> single CPU (even for that scenario profile). Then the updates to EM
> can go a bit more often (it depends what the platform would like
> to leverage and achieve w/ SW).

Thank you for the further clarification. I think the netlink 
notification should be fast and efficient enough to cover these scenarios.

Regards,
Changwoo Min