Novell LINUX ENTERPRISE SERVER 11 - ADMINISTRATION Administration Manual page 191

15.2.1 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 ACPI. There are two main approaches to
performing CPU frequency scaling—by the kernel itself or by a userspace applica-
tion. Therefore, there are different kernel governors that can be set below /sys/
devices/system/cpu/cpu*/cpufreq/.
userspace governor
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
Server distributions, this daemon is the powersaved package. When this
implementation 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
implementation is still the only working solution.
ondemand governor
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.
conservative governor
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.
powersave governor
The cpu frequency is statically set to the lowest possible.
Power Management 177