# Switch to laptop-mode on battery power - off by default as it causes odd
# hangs on some machines. (Note: This is reported to cause breakage in
# Debian - see deb bug #425800. Leaving enabled for Ubuntu for now
# since presumably it's still valid here.)
But apparently it's disabled in Ubuntu... W00t? This means that if you're running on battery power, the system doesn't perform any optimizations to reduce power consumption except for CPU frequency scaling performed by ondemand governor (please correct me if I'm wrong...).
So the first step is enabling laptop-mode (set ENABLE_LAPTOP_MODE=true in acpi-support config file) and restarting /etc/init.d/laptop-mode. A quick look at /etc/laptop/conf.d directory reveals plethora of options for tweaking laptop-mode. Many of them depend on and require specific hardware and are disabled by default; some are generic. The ones I found interesting for my laptop are:
- cpufreq.conf - configures frequency scaling rules, e.g. makes it possible to force slowest CPU frequency when running on battery power, no matter what system load is.
- start-stop-programs.conf - allows for setting programs or services which should be started or stopped when on battery power.
- ethernet.conf - configures power saving settings for Ethernet cards, e.g. limits connection speed from 1Gbit to 100Mbit.
- wireless-iwl-power.conf - configures powersave mode of Intel 3945/4965 wireless adapters.
- intel-hda-powersave.conf - configures power saving settings of Intel HDA audio chipsets.