linux-kernel - Re: [PATCH] cpufreq: Don't unregister cpufreq cooling on CPU hotplug

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Date: Fri, 1 Mar 2024 21:37:29 +0100
From: "Rafael J. Wysocki" <rafael@...nel.org>
To: Dhruva Gole <d-gole@...com>, Viresh Kumar <viresh.kumar@...aro.org>
Cc: linux-pm@...r.kernel.org, Vincent Guittot <vincent.guittot@...aro.org>, 
	Daniel Lezcano <daniel.lezcano@...aro.org>, 
	Manaf Meethalavalappu Pallikunhi <quic_manafm@...cinc.com>, Roman Stratiienko <r.stratiienko@...il.com>, 
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] cpufreq: Don't unregister cpufreq cooling on CPU hotplug

On Fri, Mar 1, 2024 at 6:50 AM Dhruva Gole <d-gole@...com> wrote:
>
> Hi,
>
> On Feb 29, 2024 at 13:42:07 +0530, Viresh Kumar wrote:
> > Offlining a CPU and bringing it back online is a common operation and it
> > happens frequently during system suspend/resume, where the non-boot CPUs
> > are hotplugged out during suspend and brought back at resume.
> >
> > The cpufreq core already tries to make this path as fast as possible as
> > the changes are only temporary in nature and full cleanup of resources
> > isn't required in this case. For example the drivers can implement
> > online()/offline() callbacks to avoid a lot of tear down of resources.
> >
> > On similar lines, there is no need to unregister the cpufreq cooling
> > device during suspend / resume, but only while the policy is getting
> > removed.
> >
> > Moreover, unregistering the cpufreq cooling device is resulting in an
> > unwanted outcome, where the system suspend is eventually aborted in the
> > process.  Currently, during system suspend the cpufreq core unregisters
> > the cooling device, which in turn removes a kobject using device_del()
> > and that generates a notification to the userspace via uevent broadcast.
> > This causes system suspend to abort in some setups.
> >
> > This was also earlier reported (indirectly) by Roman [1]. Maybe there is
> > another way around to fixing that problem properly, but this change
> > makes sense anyways.
> >
> > Move the registering and unregistering of the cooling device to policy
> > creation and removal times onlyy.
> >
> > Reported-by: Manaf Meethalavalappu Pallikunhi <quic_manafm@...cinc.com>
> > Reported-by: Roman Stratiienko <r.stratiienko@...il.com>
> > Link: https://patchwork.kernel.org/project/linux-pm/patch/20220710164026.541466-1-r.stratiienko@gmail.com/ [1]
> > Tested-by: Manaf Meethalavalappu Pallikunhi <quic_manafm@...cinc.com>
> > Signed-off-by: Viresh Kumar <viresh.kumar@...aro.org>
> > ---
>
> Makes sense to me,
>
> Reviewed-by: Dhruva Gole <d-gole@...com>

Applied (for 6.9), added a Closes: tag as suggested by Daniel.

Thanks!