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

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Message-ID: <20150731031841.GH17794@linux>
Date:	Fri, 31 Jul 2015 08:48:41 +0530
From:	Viresh Kumar <viresh.kumar@...aro.org>
To:	Radivoje Jovanovic <radivoje.jovanovic@...ux.intel.com>
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

Thanks.

I will try to add more layman terms here to map cooling state with
frequencies. So, the cooling state 0 maps to the highest frequency the
cpufreq table supports, and the highest cooling state n maps to the
lowest frequency. Right ?

On 30-07-15, 13:21, Radivoje Jovanovic wrote:
> In this case both userspace thermal solution and cpu_cooling are
> changing policy->max and the userspace solution will let governor or HW
> (depends on architecture) decide the clipped-freq. Now let us say that
> cpu_cooling has 4 available states 0-3

Lets say: 0 == 1.2 GHz
          1 == 1.1 GHz
          2 == 1 GHz
          3 == 800 MHz

> and let us say that cpu_cooling
> has set the state 1 as the last state.

i.e. cpu_cooling says "don't go over 1.1 GHz"..

> Now userspace component comes in
> and changes the state of the system that matches cpu_cooling state 0.

So, policy->max reaches 1.2 GHz and that is not in sync with
cpu_cooling. Right ?

> cpu_cooling is unaware of this change and does not change the local
> cur_state.

That's where I think you one of us might be incorrect. At this point
when policy->max is changed to 1.2 GHz, a notifier will get issued to
cpu_cooling, which will bring policy->max again to 1.1 GHz and so
things will be back in control.

> Now the temperature changes and cpu_cooling should change
> the system state to 1 (userspace component malfunctioned and is not
> picking up this change) but since the cur_state is already at 1
> cpu_cooling will not do anything since it believes it is in the correct
> state. Hope this explains it better

-- 
viresh
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