PHC

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Article summary
Provides a guide to installing, configuring and using a PHC.
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English
Related articles
Laptop
Pm-utils
CPU Frequency Scaling
Cpufrequtils

Contents

Introduction

PHC is an acpi-cpufreq patch built with the purpose of enabling arbitrarily undervolting on your processor. PHC works only if your processor's architecture supports undervolting. This is the ultimate and extreme tweak to reduce power consumption in modern PCs, therefore it's very interesting, especially for laptop computers.

For a complete power management suite see Related articles in top-right of the page.

Automatically undervolting CPUs

If you don't want to manually undervolting your CPU but let to the kernel automatically select the right frequency/voltage, you must follow the other guides listed in Related articles, specially: CPU Frequency Scaling and Cpufrequtils.

Supported CPUs

PHC supports the two most common processor families:

  • Intel
  • AMD

Intel

  • Mobile Centrino
  • Atom (N2xx)
  • Core / Core2 (T and P Series)

AMD

  • K8 series
Note: there is also a package in AUR named cpupowerd, which is somehow related to downvolting on AMD processors, check it out!

Installing the necessary packages

Install phc-intel if you have an Intel processor, or phc-k8 if you have an AMD-K8-series one.

Note: The required packages are not present in the main repository, so you must install them from the AUR. Check the wiki to learn how to use the AUR.

Install phc-intel (assuming you have an intel CPU) and phctool from the AUR.

then add "acpi-cpufreq" in the modules section of your rc.conf file, if you haven't done it before. You can edit this file using your preferred test editor, such as nano or gedit.

# nano /etc/rc.conf

Configuring PHC

Even if it's possible to configure phc using a command line interface, the configuration is much easier using phctool. Just run

# phctool

and select the "voltage" tab. Every processor has its own VID values: finding the value that fits your processor's needs is up to you.

Module loading

Run:

# dmesg | grep acpi-cpufreq

If you see errors regarding this module, something has gone wrong OR you can't use PHC.

Hardware recognition

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.

Voltage controlling

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 it's 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 find the best values, install linux-phc-optimize from AUR. The script progressively lower the values until the system crashes, and add two the values for stability. Because the system will crash, don't do anything else during the tests. Run it once for each value, then check /usr/share/linux-phc-optimize/phc_tweaked_vids.

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