Novell LINUX ENTERPRISE DESKTOP 10 SP2 - DEPLOYMENT GUIDE 08-05-2008 Deployment Manual page 560

28.3.2 Controlling the CPU Performance
The CPU can save energy in three ways. Depending on the operating mode of the
computer, these methods can be combined. Saving energy also means that the system
heats up less and the fans are activated less frequently.
Frequency and Voltage Scaling
PowerNow! and Speedstep are the designations AMD and Intel use for this tech-
nology. However, this technology is also applied in processors of other manufac-
turers. The clock frequency of the CPU and its core voltage are reduced at the same
time, resulting in more than linear energy savings. This means that when the fre-
quency is halved (half performance), far less than half of the energy is consumed.
This technology is independent from APM or ACPI. There are two main approaches
to performing CPU frequency scaling—by the kernel itself or by a userspace appli-
cation. Therefore, there are different kernel governors that can be set below /sys/
devices/system/cpu/cpu*/cpufreq/.
userspace governor
ondemand governor
conservative governor
powersave governor
544 Deployment Guide
If the userspace governor is set, the kernel gives the control of CPU frequency
scaling to a userspace application, usually a daemon. In SUSE Linux Enterprise
distributions, this daemon is the powersaved package. When this implemen-
tation is used, the CPU frequency is adjusted in regard to the current system
load. By default, one of the kernel implementations is used. However, on some
hardware or in regard to specific processors or drivers, the userspace implemen-
tation is still the only working solution.
This is the kernel implementation of a dynamic CPU frequency policy and
should work on most systems. As soon as there is a high system load, the CPU
frequency is immediately increased. It is lowered on a low system load.
This governor is similar to the on demand implementation, except that a more
conservative policy is used. The load of the system must be high for a specific
amount of time before the CPU frequency is increased.
The cpu frequency is statically set to the lowest possible.