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

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Message-ID: <20240301055042.p4jaa4v3tshlbwnb@dhruva>
Date: Fri, 1 Mar 2024 11:20:42 +0530
From: Dhruva Gole <d-gole@...com>
To: Viresh Kumar <viresh.kumar@...aro.org>
CC: "Rafael J. Wysocki" <rafael@...nel.org>, <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

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>

-- 
Best regards,
Dhruva Gole <d-gole@...com>