Undervolt your CPU - and crash your Laptop or save a lot of battery

Ok, I was constantly annoyed by the fact, that my Samsung P35 works nice and quiet and battery-savingly on Windows with a tool called CPURightmark (a tool which allows for changing the core voltage and the frequency shifting behaviour of a mobile CPU), but battery consumptive under linux. Here is the deal how to change this:

Get the Linux-PHC package version 0.3.0 from http://phc.athousandnights.de/, unpack it and follow the instructions given in the readme-file for the "module section" using the patch for the vanilla-kernel (google told me the SuSE default kernel is a modified vanilla kernel so I gave it a try and it seems to work) and your kernel number
uname -r
Remember to make a copy of your acpi-freq.ko before starting the whole process (to be found in the directory


if anything goes wrong. Copy your freshly bakened module into this folder and do a reboot. After your system is up, you should find some file entries starting with phc_ in the system folder


Now you can play around with the voltage settings by echoing new values into SysFSFilesystem as being described quite well in http://wiki.ubuntuusers.de/Prozessorspannung_absenken if you can speak German.
No warranty for your CPU, by the way. Using the lowest possible value for the lowest frequency step, I could decrease the temperature of my CPU by almost 5°C - now I'm still trying to figure out how to tell my laptop to spin up the fan at higher temperatures to get it quiet - my next post will probably deal about that.

Be careful not to take too low values for the voltage, since this might make your system unstable - I warned you...

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