linux-kernel - Re: [PATCH] thermal/cpu_cooling: remove local cooling state variable

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Date:	Sat, 1 Aug 2015 17:04:05 +0530
From:	Viresh Kumar <viresh.kumar@...aro.org>
To:	Radivoje Jovanovic <radivoje.jovanovic@...ux.intel.com>,
	"Rafael J. Wysocki" <rjw@...ysocki.net>
Cc:	Punit Agrawal <punit.agrawal@....com>, rjw@...ysocki.net,
	LKML <linux-kernel@...r.kernel.org>,
	Linux PM <linux-pm@...r.kernel.org>,
	Zhang Rui <rui.zhang@...el.com>,
	Eduardo Valentin <edubezval@...il.com>,
	Radivoje Jovanovic <radivoje.jovanovic@...el.com>
Subject: Re: [PATCH] thermal/cpu_cooling: remove local cooling state variable

On 31-07-15, 08:30, Radivoje Jovanovic wrote:
> I just looked over the notifier in the current upstream (my patch was
> made on our production kernel which is 3.14 and has old notifier
> implementation with notifier_device in place) and I see your point.

That's disappointing. You were expected to check if the same problem
exists in mainline.

> I agree with you that this patch is trivial for the current
> implementation since the notifier, as it is currently, will enforce
> cpu_cooling policy change at every CPUFREQ_ADJUST which would cause
> problems in our current implementation. In our implementation there is
> a cpufreq driver that will also change policies during CPUFREQ_ADJUST,
> once the request comes from the underlying FW so there would be a fight
> who gets there first since cpu_cooling will change the policy in
> CPUFREQ_ADJUST notifier_chain and the driver would do the same thing.
> It seems to me that better implementation of the cpu_cooling notifer
> would be to keep the flag and change the policy in CPUFREQ_ADJUST only
> when the change was requested by cpu_cooling, and update the current
> state of cpufreq_cooling_device during CPUFREQ_NOTIFY event.
> What do you think?

I think the way cpu-cooling is written today, is an *ugly* hack. We hack
the notifier to change policy->max and no one is notified for it.

That's crap.

I would rather get some help from cpufreq core on that. Which can
provide some APIs to take care of thermal considerations.

Okay, I push that to my todo list. Will keep you all posted.

-- 
viresh
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