Yes of course!

Sorry for that ;)

Best,

Francesco ________________________________________ From: Mike Turquette [mturquette@linaro.org] Sent: Thursday, July 25, 2013 7:36 PM To: Comaschi, F. Subject: Re: Arndale power management

Francesco,

Can you reply to the list with your response? Please do not remove the list when responding.

Regards, Mike

On Wed, Jul 24, 2013 at 11:11 PM, Comaschi, F. fcomaschi@tue.nl wrote:

Dear Mike,

thank you very much for your reply!

the hack that you suggest is indeed what I have done so far just for testing. However, I was thinking, if we have some knowledge about the specific application that we are running, from a functional point of view (e.g., we are scanning a scene through a camera and we see that there's no movement, therefore we decide to lower the frequency), wouldn't it be useful to exploit this knowledge in order to implement our own DVFS policy in a more proactive way, rather than recurring to the available governors which I think are working in a more reactive way? In that case, how would you suggest to interface with the OS from inside my application? Shall I make some "calls" to specific API's, or maybe writing my own governor?

Thanks in advance for your attention!

Best,

Francesco ________________________________________ From: Mike Turquette [mturquette@linaro.org] Sent: Thursday, July 25, 2013 3:58 AM To: Viresh Kumar; Comaschi, F. Cc: Lukasz Majewski; Lists linaro-kernel; cpufreq@vger.kernel.org; Chander Kashyap; Linux PM List Subject: Re: Arndale power management

Quoting Viresh Kumar (2013-07-15 23:43:03)

...

Adding few more lists so that others can also help..

On 15 July 2013 20:00, Comaschi, F. fcomaschi@tue.nl wrote:

...

Dear Viresh,

I am Francesco Comaschi, a researcher at Eindhoven University of Technology. My research group is interested in implementing custom power management policies on ARM-based platform (at the moment we are using an Arndale 5250 board featuring Exynos5 dual). We would like to make use of DVFS and to be able to measure power consumption on the board.

Ok.

...

First of all, congratulations for the work that you and the other guys form the power management team are doing within the Linaro community, I always follow your progress, and so far you have been the only reliable source of information for everything I have been doing on the board.

Thanks :)

...

If you do not mind, I would like to ask you a few questions:

1. Is there a way to measure the board power consumption via software? I have read here: http://blogs.arm.com/software-enablement/925-linux-hwmon-power-management-an... that it is possible with the ARM Versatile boards, through the hwmon framework and lm_sensors. However, when I run lm_sensors on the Arndale board, no sensors were found. Do you know about any other possible ways to measure power in software? Maybe it is possible to communicate with the on-board PMIC? Maybe there are some registers where information about the power/voltage provided to the processor and the other components is available?

On ARM Versatile express boards and the coretiles that come with it, we have sensors which are probed through hwmon framework in Linux. So, we have hardware IPs present on board which let us get some power figures per cluster for big LITTLE.

I am not sure if Exynos have any such things on it.

@Chander: Are you aware of any such features?

...

2. Recently I have read Andy Green’s presentation “How to measure SoC power”. However, by measuring power on the PMIC input side through the ARM Energy Probe, probably I won't be able to see the effect of DVFS. Do you have any suggestions on how to measure the effect of DVFS, even through hardware measurements?

You need probes on the voltage regulator which is feed the cores... But again, that is very much hardware specific. And I haven't worked on Exynos at all :)

...

3. More in general, I do not know which is the best way to implement custom policies of DVFS.

I didn't get you here. Are you talking about tuning of governors here?

...

Is it possible, maybe through appropriate API's, to access the cpu_idle and the cpu_freq framework from inside my application? Shall I work directly with the drivers of the PMIC? Is it possible to set the voltage directly from inside my application?

Are you trying to create a DVFS policy from a userspace application? Lots of people hack together something using the CPUfreq "userspace" governor and writing to: /sys/devices/system/cpu/cpu0/cpufreq/scaling_governor

This is not something that should be shipped on a product but is useful for learning and prototyping. It only affects the CPU and will not help you craft DVFS policies on other peripherals/devices.

Regards, Mike

...

Something on the board must provide this to kernel. Kernel can't get it by itself.

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