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

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Message-ID: <040a0850-a686-42c3-832c-07494cac8ef0@arm.com>
Date: Thu, 22 May 2025 09:43:08 +0100
From: Lukasz Luba <lukasz.luba@....com>
To: Changwoo Min <changwoo@...lia.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 09:35, Changwoo Min wrote:
> 
> 
> 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.

Yes, I agree