Novell LINUX ENTERPRISE SERVER 10 - INSTALLATION AND ADMINISTRATION 11-05-2007 Installation Manual page 528

/proc/acpi/thermal_zone/*/cooling_mode
Select the cooling method controlled by ACPI. Choose from passive (less perfor-
mance, economical) or active cooling mode (full performance, fan noise).
/proc/acpi/thermal_zone/*/trip_points
Enables the determination of temperature limits for triggering specific actions, like
passive or active cooling, suspension (hot), or a shutdown (critical). The
possible actions are defined in the DSDT (device-dependent). The trip points deter-
mined in the ACPI specification are critical, hot, passive, active1, and
active2. Even if not all of them are implemented, they must always be entered
in this file in this order. For example, the entry echo 90:0:70:0:0 >
trip_points sets the temperature for critical to 90 and the temperature
for passive to 70 (all temperatures measured in degrees Celsius).
/proc/acpi/thermal_zone/*/polling_frequency
If the value in temperature is not updated automatically when the temperature
changes, toggle the polling mode here. The command echo X >
/proc/acpi/thermal_zone/*/polling_frequency causes the temper-
ature to be queried every X seconds. Set X=0 to disable polling.
None of these settings, information, and events need to be edited manually. This can
be done with the Powersave daemon (powersaved) and its various front-ends, like
powersave, kpowersave, and wmpowersave. See
(page 512).
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-
510 Installation and Administration
Section 28.3.3, "ACPI Tools"