Linux: CPU frequency scaling in Linux with cpufreq
Knocked off from a very useful page I found: http://www.pantz.org/software/cpufreq/usingcpufreqonlinux.html
Here are some notes on getting CPU frequency scaling working on Linux. CPU frequency scaling does what it sounds like. It will raise and lower the frequency of your processor depending on a set level of demand being made on the processor at the time. One of the reasons you might want to do this would be to save energy. This could save you money on your electric bills or battery life on a laptop. It will also lower the temperature of your processor(s) to keep your machine cooler.
The following examples are done using K/X/Ubuntu distribution using a 2.6.24 kernel. Most of the settings in the examples should be the same or close to the same for any other distros. I will use apt-get the package manager installed with K/X/Ubuntu for the software install examples. You will need to use whatever package manager yours system uses. Yum (RPM) and apt-get (dpkg) are 2 very popular ones.
Before we start if you have a RedHat or Fedora machine you might want to try to install cpuspeed (yum install cpuspeed) to get frequency scaling. In K/X/Ubuntu or another Debian based machine you might just try to install cpufrequtils (sudo apt-get install cpufrequtils) to get frequency scaling working. If that does for you then you don't need to go through the parts of finding and loading the correct modules below. Just skip to the section on configuring the scaling governor.
Kernel version
Make sure your kernel version is at least 2.6.12 to make use of all the possible governors that will be mentioned. All of the frequency scaling will be done with kernel modules and not user space governors.
Enable support in your BIOS
Enter your BIOS and make sure Cool'n'Quiet (AMD) or SpeedStep (Intel) is enabled for you CPU. Some BIOS's may not have an option for either. If you don't find the option it is probably enabled by default. Unfortunately your BIOS may have the option but it is listed as another name altogether. If that is the case check your BIOS's manual for more information.
Remove any userspace CPU scaling programs
There are some userspace programs that can be run to scale the processors frequency. We will be scaling the CPU with the kernel so we don't need these. So if you have any we are going remove them now. You may want to look into these as they can be helpful in certain situations. This article will deal with just using the kernel modules to scale.
sudo apt-get remove powernowd cpudyn cpufreqd powersaved speedfreqd
Install the module for your CPU
When you installed your system there is a very good chance your CPU was detected by default and the module you need for for scaling is already running. Below is a command that will help you identify what type of processor(s) you have.
cat /proc/cpuinfo
After you know this then you will know what kernel module you will need to load for it. Here is the command to see what kernel modules are loaded.
lsmod
Below are CPU descriptions and the commands used to load the kernel modules based on what processor you have. Look at the output from lsmod above and use the modules names after the word "modprobe" below to see if you already have a module loaded. If you do then just move on to the next step. If not then use the CPU info you found and figure out which module you need to load. Then run the command to load it.
CPU: PIII-M or P4 without est. 2 module types for this.
sudo modprobe speedstep-ich or sudo modprobe speedstep-smi
CPU: Intel Core Duo, Intel Core2 Duo or Quad, or Intel Pentium M. This has been merged into the acpi-cpufreq module in later kernels.
sudo modprobe speedstep-centrino
CPU: Intel Celeron, Xeon, and Pentium 4 processors
sudo modprobe p4_clockmod
CPU: AMD K6. Socket Type: Socket 7
sudo modprobe powernow-k6
CPU: AMD Sempron/Athlon/MP ( K7 ). Socket Types: A, Slot A.
sudo modprobe powernow-k7
CPU: AMD Duron/Sempron/Athlon/Opteron 64 ( K8 ). Socket Types: 754, 939, 940, S1 ( 638 ), AM2 ( 940 ), F ( 1207 ).
sudo modprobe powernow-k8
CPU: VIA CentaurHauls* or Transmeta GenuineTMx86*
sudo modprobe longhaul
As a last resort if any of these don't work you can try the generic one for ACPI. More drivers are getting moved to this module in later kernels like speedstep-centrino after 2.6.20.
sudo modprobe acpi-cpufreq