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

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Message-ID: <CAJZ5v0jiAHHLP2O_0ZkXPPCXq9tFTxqrap1mFXOJtKuBo-gJfw@mail.gmail.com>
Date: Sat, 10 May 2025 13:34:29 +0200
From: "Rafael J. Wysocki" <rafael@...nel.org>
To: Changwoo Min <changwoo@...lia.com>
Cc: "Rafael J. Wysocki" <rafael@...nel.org>, Lukasz Luba <lukasz.luba@....com>, 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
Subject: Re: [PATCH v2] PM: EM: Add inotify support when the energy model is updated.

On Sat, May 10, 2025 at 7:07 AM Changwoo Min <changwoo@...lia.com> wrote:
>
> Thank you, Rafael, for the pointer.
>
> On 5/10/25 01:41, Rafael J. Wysocki wrote:
> >>
> >> I have discussed that with Rafael and we have similar view.
> >> The EM debugfs is not the right interface for this purpose.
> >>
> >> A better design and mechanism for your purpose would be the netlink
> >> notification. It is present in the kernel in thermal framework
> >> and e.g. is used by Intel HFI
> >> - drivers/thermal/intel/intel_hfi.c
> >> - drivers/thermal/thermal_netlink.c
> >> It's able to send to the user space the information from FW about
> >> the CPUs' efficiency changes, which is similar to this EM modification.
> >
> > In addition, after this patch
> >
> > https://lore.kernel.org/linux-pm/3637203.iIbC2pHGDl@rjwysocki.net/
> >
> > which is about to get into linux-next, em_dev_update_perf_domain()
> > will not be the only place where the Energy Model can be updated.
>
> 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.