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I learnt that we can change P-state governors with the command echo "ondemand" > /sys/devices/system/cpu/cpu0/cpufreq/current_governor

How dooes one change the C state governor ?

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3 Answers

I don't believe that you can govern the C state from the OS.

If the CPU supports it, then it will enter lower powered states automatically, BIOS permitting.

But it doesn't make so much sense applying a governor to it in the same way that you control how P states ramp up and down depending on active usage.

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I have heard of ladder governors and menu governors that govern C states. So i was curious to know how to change the current governor from ladder governor to menu governor –  kashyapa Nov 3 '09 at 16:02
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Check out this article on C,P, and T-states for power/cpu frequency scaling management.

The long and short of it is from the article is

* cd /sys/devices/system/cpu
* ls -L
* cd cpux/cpufreq
* cat scaling_available_frequencies
* echo -n xxxxx > scaling_max_freq
* echo -n yyyyy > scaling_min_freq

http://greentechnologyinsights.blogspot.com/2009/02/processor-power-management-in-linux.html

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What I wanted to know was actually this : If my current C-state governor is ladder governor, How do you change settings so that my C-state governor shall be menu governor (say) –  kashyapa Nov 3 '09 at 15:50
    
Sorry about that, I missed what you were getting at somehow, even though its clear. I am pretty sure that the c state governor is only a compile time option in the Linux kernel. If anyone knows differently I would be interested to hear it. :) –  MattyB Nov 3 '09 at 16:28
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up vote 0 down vote accepted

it can be changed by going into /sys/devices/system/cpu/cpuidle directory and changing the file scaling_governor from ladder to menu (say)

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