Novell LINUX ENTERPRISE SERVER 10 SP2 - INSTALLATION AND ADMINISTRATION Installation Manual page 533

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
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.
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.
performance governor
The cpu frequency is statically set to the highest possible.
Throttling the Clock Frequency
This technology omits a certain percentage of the clock signal impulses for the
CPU. At 25% throttling, every fourth impulse is omitted. At 87.5%, only every
eighth impulse reaches the processor. However, the energy savings are a little less
than linear. Normally, throttling is only used if frequency scaling is not available
or to maximize power savings. This technology, too, must be controlled by a special
process. The system interface is /proc/acpi/processor/*/throttling.
Power Management 515