Power management/Processor

This article describes the setup of power management for processors.

CPU frequency scaling
CPU frequency scaling is a technique whereby the frequency of a processor can be automatically adjusted "on the fly" to conserve power and to reduce the amount of heat generated by the chip.

BIOS
Some functions can be enabled or disabled in the BIOS. Check that them are enabled, e.g.:
 * Processor C1E support
 * Enhanced Speedstep (EIST)

Kernel
You need to activate the following kernel options:

You need a governor, who changes the frequency based on his profile:

Ticks
The processor saves the most energy when the processor stays longer in power savings modes, so you have to reduce the amount of ticks that wakes the processor up.

BIOS
Some functions can be enabled or disabled in the BIOS. Check that they are enabled, e.g.:
 * HPET
 * Multimedia timer

Kernel
You need to activate the following kernel options:

PowerTOP
PowerTOP is a utility designed to measure, explain and minimise a computer's electrical power consumption.

Software
Install :

I used a few time -1 before and the software was pretty good at giving good advise on what power management options to set up depending on the system usage. Now, version 2 become very good in that I nearly get 10-15° less CPU temperature enabling every power management option which is almost what I can get on cold weather (~40°C) while my laptop runs almost at 50-55°C in summer (quite hot... compiling/chunking around C++ objetcs make it jump to almost 100°C! (qt-libraries, libreoffice, chromium) or simply with Wifi card on). With everything enabled, the CPU runs almost all the time (when no power hungry application is running obviously) at idle or the lowest C-state (800MHz). I could not expect better. The spot that is missing is a deamon-ish application or at least a configuration/profile file that PowerTOP will pick up at start up. Lets submit the idea to upstream.

Usage
powertop - Sorts the running processes in order how often they cause the processor to wake up.

Hprofile
When one needs to change the CPU governor, one could just use a simple command such as the following which nullify the usage of sys-power/cpupower or other CPU governor and frequency utilities.

However, that kind of command incanatation needs a little automation... think if you're using a laptop and want it to be a little dynamic in power saving mode, you will surely want a power saving profile if the laptop is not wired to AC power. This is where Hprofile comes into play, follow reading in that article for more information.