Undervolt your notebook CPU for longer battery life

“Undervolting is the practice of reducing the supply voltage of a computer’s CPU. There are mainly three reasons to do so:

1. Reduce power consumption
2. Reduce heat generation
3. Reduce fan noise

From Ubuntu Jaunty 9.04 on the ACPI stuff is now in the kernel rather than in a module which requires you to patch and build the kernel sources. Latest distribution kernel patched can be downloaded straight from the PHC PPA: https://launchpad.net/~linux-phc/+archive/ppa

and automatically adding the following line to sources list:

ppa:linux-phc/ppa

then installing them via

sudo  apt-get install  linux-generic-phc linux-headers-generic-phc

(deb http://ppa.launchpad.net/linux-phc/ppa/ubuntu lucid main
deb-src http://ppa.launchpad.net/linux-phc/ppa/ubuntu lucid main

Signing key: 1024R/4D950ED1

[in order to automatically add the signing key have a look at this post]

3. Reboot. If the module is installed correctly, then look here for phc related files

/sys/devices/system/cpu/cpu0/cpufreq/

One should be like this one (values would be of course different):

12:38 10:30 8:24 6:18

UPDATE: Reached this point in Ubuntu Lucid you have to compile the module yourself. It’s as easy as typing 3 words. You could refer to Dan Mihai excellent post liked above for the complete explanation.

In order to minimize any possibility of data corruption I advise you to run this script from Ubuntu Safe Mode / Recovery mode (choose this at boot menu, then root terminal when prompted, if you have no boot menu keep pressed SHIFT / MAIUSC right after powering on the computer). Here you will have a terminal only environment, which also lacks any cpu management module. Remember you are in a root environment, here you may also do system wide damages! Be careful with the commands you type in!

First ensure you have phc-intel module loaded

modprobe phc-intel

If you haven’t granted execution to the script before do it now

# chmod u+x linux-phc-optimize.bash

cat /sys/devices/system/cpu/cpu0/cpufreq/phc_controls

Then run the scripts the terminal with

The value before the: stands for the frequency, the later for the voltage.

4. Okay, now we need to find the lowest save voltages. We will use this optimizer script.
Download it then right-click the files, open the permissions tab, and and down at the bottom check the box that says “allow executing the file…”.

It needs cpuburn installed, so you might want to install it in advance with synaptic. If you haven’t done so yet

$ sudo ./linux-phc-optimize.bash

# apt-get install cpuburn

What this scipt does is: It stresses your cpu while lowering the cpu voltage step by step unil your system crashes. Then the script knows what is too low and will stay safely above. The script needs to run once for every frequency step your cpu is capable of, usually around 4-6 times. It will tell you, just run it so often until it tells you finished.

In case you have a dual core CPU it is advisable to run two instances of cpuburn,

first run

cpuburn &

then run the script (which will run the other instance)

NOTICE:
This script will crash your system. Several times. This is normal and intended. No harm to your hardware is to be expected. However in case you have open files and / or mounted filesystems data loss or corruption might occur. So be advised to unmount as many partitions as possible and open as few files as necessary while doing this. After a reset the fsck utility will check your partitions for data corruption so be strongly advised to let that check run!

All this is not going to occour if you run the script from the recovery mode

Second, the script stresses only one cpu core. In case you have a dual core, open a terminal and type “burnMMX” to run a second thread to stress the second core while doing this.

When you’re finished with the script, you will have a text file with the new and optimized frequency : voltage pairs.

5. To use these optimized values, you will need to echo them to /sys/devices/system/cpu/cpu0/cpufreq/phc_controls. An easy way to do it automatically every reboot is to add a line like this:

to your /etc/rc.local file. Of course you have to replace the values with your own. Any second core should automatically use the same voltages.

6. Check if it works:

cat /sys/devices/system/cpu/cpu0/cpufreq/phc_controls

Related posts:

1. nVidia PowerMizer powersaving/cooling in Linux (updated)
2. eee-control – the best device control tray icon for Eee-PCs