Cool'n'Quiet, Mandriva Linux 2008

I have an AMD Athlon X2 5600.

I found that as soon as my Linux box used some CPU time and got a bit warm as a result it would increase the CPU fan speed to 3,000 RPM or more. As expected. However, it would then never drop back down to the 2,000 RPM idle speed.

The reason is that the kernel defaults to 'performance' mode for cool'n'quiet.

Take a look at:
# cat /sys/devices/system/cpu/cpu0/cpufreq/scaling_governor

To see what your kernel/CPU supports:
# cat /sys/devices/system/cpu/cpu0/cpufreq/scaling_available_governors

To enable a near instant change of fan speed when the CPU usage drops, try:
# echo "ondemand" > /sys/devices/system/cpu/cpu0/cpufreq/scaling_governor
# echo "ondemand" > /sys/devices/system/cpu/cpu1/cpufreq/scaling_governor

I'm not sure what performance issues this may have. But my machine is quiet again now. I'm researching cpufreqd and trying to userstand how this all works, and will report back!