Novell LINUX ENTERPRISE SERVER 10 - INSTALLATION AND ADMINISTRATION 11-05-2007 Installation Manual page 530

only be applied if no other device modifies the contents of the main memory via
bus master activity. Some drivers prevent the use of C3. The current state is dis-
played in /proc/acpi/processor/*/power.
Frequency scaling and throttling are only relevant if the processor is busy, because the
most economic C state is applied anyway when the processor is idle. If the CPU is busy,
frequency scaling is the recommended power saving method. Often the processor only
works with a partial load. In this case, it can be run with a lower frequency. Usually,
dynamic frequency scaling controlled by the kernel ondemand governor or a daemon,
such as powersaved, is the best approach. A static setting to a low frequency is useful
for battery operation or if you want the computer to be cool or quiet.
Throttling should be used as the last resort, for example, to extend the battery operation
time despite a high system load. However, some systems do not run smoothly when
they are throttled too much. Moreover, CPU throttling does not make sense if the CPU
has little to do.
In SUSE Linux Enterprise these technologies are controlled by the powersave daemon.
The configuration is explained in
28.3.3 ACPI Tools
The range of more or less comprehensive ACPI utilities includes tools that merely display
information, like the battery charge level and the temperature (acpi, klaptopdaemon,
wmacpimon, etc.), tools that facilitate the access to the structures in /proc/acpi or
that assist in monitoring changes (akpi, acpiw, gtkacpiw), and tools for editing the ACPI
tables in the BIOS (package pmtools).
28.3.4 Troubleshooting
There are two different types of problems. On one hand, the ACPI code of the kernel
may contain bugs that were not detected in time. In this case, a solution will be made
available for download. More often, however, the problems are caused by the BIOS.
Sometimes, deviations from the ACPI specification are purposely integrated in the
BIOS to circumvent errors in the ACPI implementation in other widespread operating
systems. Hardware components that have serious errors in the ACPI implementation
are recorded in a blacklist that prevents the Linux kernel from using ACPI for these
components.
512 Installation and Administration
Section 28.5, "The powersave Package" (page 515).