> i experience on my Thinkpad X200, that sometimes the fan gets stuck at > fullspeed. (This time it is after 19h of uptime.) > The notebook is idle, temperatures are fine, but the fan just goes to > fullspeed and stays there. > Normaly the regulation works fine in tandem with apmd -C. > Rebooting will reset the fan to normal behaviour.
nothing controls fan speeds in the kernel. the thinkpad embedded controller defaults to "auto" mode, which is supposed to regulate fan speeds itself and speed up or slow down depending on cpu and hdd temperatures. you can usually hear it speed up while doing cpu-intensive tasks, but unfortunately it will never slow down enough that you can't hear it. you can try checking if there are any EC/BIOS updates for your laptop on lenovo's website. otherwise, you can force the fan down in the kernel. just last night i wrote this to quiet down my idle thinkpad x301 by turning the fan down when the temperatures are low: http://jcs.org/patches/openbsd-acpithinkpad_fan_control.diff but use it at your own risk and don't expect it to be committed. it could probably use some sysctl knobs to define the max temperatures, but the hard-coded ones are working ok for me right now.
