PHC is an acpi-cpufreq patch built with the purpose of enabling undervolting on your processor. This can potentially divide the power consumption of your processor by two or more, and in turn increase battery life and reduce fan noise noticiably. PHC works only if your processor's architecture supports undervolting.
Alternative to PHC
AUR is a userland solution to replace the in-kernel cpufreq governors and also enable undervolting, only on AMD processors. Like PHC, it requires the user to find safe voltages by himself.
PHC supports the following processor families:
- Mobile Centrino
- Atom (N2xx)
- Core / Core2 (T and P Series)
- Core i (tested on Core i3 550)
- K8 series
Installing the necessary packages
Install from the AUR either AUR if you have an Intel processor, or AUR if you have an AMD-K8-series one.
Next you need to compile the module for your kernel; this will also be necessary after a kernel update.
You need to haveand/or installed to be able to build the module.
# phc-intel setup
# rc.d setup phc-k8
Finding safe low voltages
To automatically find the best voltages, you can use the mprime-phc-setup script (source-code). Just copy the code into a text file, chmod +x it to make it executable and run it. You need to install AUR first (it is used to check that the CPU is stable). This script has not been tested on many systems yet, but should be safe.
You can also try some setups. The script progressively lowers the values until the system crashes, and adds two to the values for stability. Because the system will crash, do not do anything else during the tests. Run it once for each value, then check
Editing the configuration
After the phc module is compiled and the lowest voltages are found, they need to be added to the configuration file at
VIDS="25 22 15 8 5"
If you are still running a sysvinit configuration, then just restart the phc daemon:
# rc.d start phc-intel
# rc.d start phc-k8
In case you are using systemd (recommended), simply restart the system and the modules will be loaded and setup automatically.
$ dmesg | grep acpi-cpufreq
If you see errors regarding this module, something has gone wrong OR you cannot use PHC.
There should be some files in
/sys/devices/system/cpu/cpu0/cpufreq/ beginning with "phc_".
To check whether PHC is working or not, just type:
$ cat /sys/devices/system/cpu/cpu0/cpufreq/phc_controls
you should read some values. If the values do not appear, then PHC is probably not supported by your CPU.
You can easily check whether PHC is working or not by looking at the cpu voltages: if the voltages are lower than the normal ones, then PHC has done its job. You can also manually set voltages, for example:
# echo 34 26 18 12 8 5 > /sys/devices/system/cpu/cpu0/cpufreq/phc_vids
To make sure that your undervolted CPU is stable, you can run long sessions ofAUR and/or AUR (Intel-only).