[ltp] t42 archlinux fan noise

[Henrique de Moraes Holschuh]

On Mon, 26 Oct 2009, Arian Kuschki wrote:
> I have been using Ubuntu for a couple of years on an x31 and a t42 
> without any problems. But now I switched to Arch Linux and for some 
> reason then fan on my t42 is always running around 3500 rpm even when the laptop is 
> idle for hours (cpu load < 5%). Only very seldomly does it go down to 
> 3000rpm.

What is the output of "cat /proc/acpi/ibm/fan" ?

What is the output of "grep . /sys/module/thinkpad_acpi/parameters/*" ?
(might need to be run as root).

> I know there are programs like fancontrol to control fan speed, but I 

Which you shouldn't use unless you have a real need for them...

> all support for fan regulation on ThinkPads is built into the Kernel 

ThinkPads have fan regulation in firmware, they need absolutely no help
whatsoever from the kernel or from any application to regulate the fan as
long as you leave it in "auto" mode.

This is not true on thinkpads that have hardware defects that cause the CPU
to heat up way too much and trip one of the defenses ("thermal trip
points").  These require help from the kernel "thermal" driver to work
right, and we have had bugs in that area in the past...  many of them
related to BIOS bugs, BTW.

The kernel driver (thinkpad-acpi) allows you to override the firmware fan
control if you need to for some reason (or if you don't agree with the
decisions done by the firmware -- this is my case, I like more aggressive
cooling to start well before my CPU hits 70°C).  Do notice that once you
tell the firmware that you want the fan at a given level, it will remain
there.  This can cause hardware damage if anything inside heats up too much.

Distros REALLY should not be enabling any fan control application by
default!  It is something that only the local administrator is supposed to
do.

> Does anybody know how Ubuntu handles the Thinkpad fan out of the box? If 

It leaves the fan control alone by default, as it should.  At least AFAIK.

Do notice archlinux might have screwed up cpuidle or C-state control, or the
GPU power management, all of which would mean your thinkpad is running a lot
hotter than it otherwise would.

> there is no other way but to run a script to control fan speed, which 
> one do you recommend? Under Arch Linux I think fancontrol is the 

Look in thinkwiki.org.  I recommend using no continuous fan control script
whatsoever, and binding a hotkey to kick the fan to level 7 (and back to
level AUTO) when you need some extra cooling or don't need extra cooling
anymore.

Make sure you are using the latest T42 firmware (BIOS and EC).

> preferred option. And also, if I have to adjust fan speed manually, 
> where can I find information about critical temperature thersholds for a 
> t42.

These are not documented.  And sometimes they are NOT constant (I do think
they are constant on the T4x, though... but I am not _sure_ about it).

-- 
  "One disk to rule them all, One disk to find them. One disk to bring
  them all and in the darkness grind them. In the Land of Redmond
  where the shadows lie." -- The Silicon Valley Tarot
  Henrique Holschuh