If you have Debian lenny platform and want to decrease server CPU  power consumption, lowering temperatures and fan speed:

modprobe acpi-cpufreq

but first of all you should check your CPU capabilities:

cat /sys/devices/system/cpu/cpu0/cpufreq/scaling_available_frequencies
2660000 2527000 2394000 2261000 2128000 1995000 1862000 1729000 1596000 1463000 1330000 1197000

current CPU frequency:

cat /proc/cpuinfo | grep MHz
cpu MHz : 2660.000
cpu MHz : 2660.000
cpu MHz : 2660.000
cpu MHz : 2660.000

cat /sys/devices/system/cpu/cpu0/cpufreq/scaling_available_governors
performance

also you should load ondemand governor:

modprobe cpufreq_ondemand

now: cat /sys/devices/system/cpu/cpu0/cpufreq/scaling_available_governors

ondemand performance

OK, now we need enable new feature ondemand:

echo ondemand > /sys/devices/system/cpu/cpu0/cpufreq/scaling_governor

Done.

To make permanent changes: echo acpi_cpufreq >> /etc/modules && echo cpufreq_ondemand >> /etc/modules

you could also use sysfsutils for this:

echo “devices/system/cpu/cpu0/cpufreq/scaling_governor = ondemand” >>  /etc/sysfs.conf