Today, I discovered a gem added to the 2.6.9 Linux kernel by Intel engineer Venkatesh Pallipadi: the Ondemand cpufreq governor. This kernel module uses the Enhanced SpeedStep Technology available with Pentium M processors to rapidly change the CPU speed, based on current load.

cpuspeed does the same thing, but takes noticeably longer to reach the maximum speed, and also waits longer before slowing down again. X applications feel much faster with Ondemand, and my guess is that battery life will be slightly better.

So if you have an Intel CPU with Enhanced SpeedStep Technology and want to give Ondemand a try, stop any running cpufreq daemons, like cpuspeed or cpudyn, and run the following commands. Note that I have only tested this on Fedora Core 3 with the 2.6.11-1.14_FC3 kernel.

/sbin/modprobe cpufreq_ondemand
echo ondemand > /sys/devices/system/cpu/*/cpufreq/scaling_governor

You can then start

watch -n 1 cat /sys/devices/system/cpu/*/cpufreq/scaling_cur_freq

in a terminal window, and run some X application to see how Ondemand changes the CPU speed.

To permanently install Ondemand, make sure that the cpuspeed service is turned off, and add the above modprobe and echo commands to /etc/rc.d/rc.local.

If you want to switch back to cpuspeed for some reason, you can deactivate Ondemand by running

echo userspace > /sys/devices/system/cpu/*/cpufreq/scaling_governor