Enabling power management on Debian

Debian 5 supports CPU power management, but it is not installed by default, at least when using the most basic install (for example, for use as an NFS server).

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Installation of CPU Power Management Components

apt-get install cpufrequtils sysfsutils

Configuration of CPU Power Management Policy

Determine the CPU type,

cat /proc/cpuinfo | grep "model name"

Enable the correct driver for the CPU type using modprobe (see table below), for example

modprobe p4_clockmod

Select the desired power saving mode (the 'CPU Policy Governor', see table below), for example

modprobe cpufreq_conservative

Determine the list of CPUs present (for example cpu0 and cpu1 might be reported),

dir /sys/devices/system/cpu

Apply the policy to the CPU(s). Note that this must be applied to each cpu reported above,

echo conservative | tee /sys/devices/system/cpu/cpu0/cpufreq/scaling_governor
echo conservative | tee /sys/devices/system/cpu/cpu1/cpufreq/scaling_governor

Confirm the configuration:

cpufreq-info

Permanent Configuration

Apply the driver and power save mode to /etc/modules (see tables below for parameters),

echo p4_clockmod | tee -a /etc/modules
echo cpufreq_conservative | tee -a /etc/modules

Enable the policy by editing /etc/sysfs.conf using nano. Add a line for each cpu reported using the desired policy per table above,

devices/system/cpu/cpu0/cpufreq/scaling_governor = conservative
devices/system/cpu/cpu1/cpufreq/scaling_governor = conservative

Power Management Values

CPU Type	Driver Name	`modprobe` example	`/etc/modules` example
AMD K6	`powernow_k6`	`modprobe powernow_k6`	`echo powernow_k6 \| tee -a /etc/modules`
AMD K7	`powernow_k7`	`modprobe powernow_k7`	`echo powernow_k7 \| tee -a /etc/modules`
AMD K8	`powernow_k8`	`modprobe powernow_k8`	`echo powernow_k8 \| tee -a /etc/modules`
Generic Driver	`acpi_cpufreq`	`modprobe acpi_cpufreq`	`echo acpi_cpufreq \| tee -a /etc/modules`
Pentium M	`speedstep_centrino`	`modprobe speedstep_centrino`	`echo speedstep_centrino \| tee -a /etc/modules`
Pentium 4	`p4_clockmod`	`modprobe p4_clockmod`	`echo powernow_k6 \| tee -a /etc/modules`

Policy Name	Description	`modprobe`
`cpufreq_performance`	Maintains the highest speed - no power saving	`modprobe cpufreq_performance`
`cpufreq_powersave`	Maintains the lowest speed - maximum power saving	`modprobe cpufreq_powersave`
`cpufreq_ondemand`	Dynamic adjustment, tailored for performance	`modprobe cpufreq_ondemand`
`cpufreq_conservative`	Dynamic adjustment, tailored for power saving	`modprobe cpufreq_conservative`

Policy Name	Permanent example	`/etc/sysfs.conf`
`cpufreq_performance`	`echo cpufreq_performance \| tee -a /etc/modules`	`devices/system/cpu/cpu0/cpufreq/scaling_governor = performance`
`cpufreq_powersave`	`echo cpufreq_powersave \| tee -a /etc/modules`	`devices/system/cpu/cpu0/cpufreq/scaling_governor = powersave`
`cpufreq_ondemand`	`echo cpufreq_ondemand \| tee -a /etc/modules`	`devices/system/cpu/cpu0/cpufreq/scaling_governor = ondemand`
`cpufreq_conservative`	`echo cpufreq_conservative \| tee -a /etc/modules`	`devices/system/cpu/cpu0/cpufreq/scaling_governor = conservative`