Correct fan regulation with a T420s in Kubuntu 11.10 Beta2 - Needed only kernel parametres.

Question

My brand new T420s (Manufactured September 7) is a model 4174P4G with a working Win7 fan regulation. There an idle machine has a fan RPM of ~2000 at a CPU temperature of ~40 C in a 23 C room. Those figures are the same whether I choose to use "NVIDIA Optimus" or only the "Integrated Graphics". If I use the "Discrete Graphics" in Win7, idle temperature of the CPU lies between 45-50 C and the fan runs at ~3500-3600 RPM. This is due to the Nvidia GPU, which also lies at ~45-50 C while idle.
Booting a USB stick with the Kubuntu 11.10 Beta2 Live DVD while doing nothing with kernel parametres, produces a cool fan exhaust with "Integrated Graphics" and a slightly hot one with "NVIDIA Optimus". I did not test much with "Discrete Graphics" since the open source driver failed to work, and the closed source Nvidia driver wouldn't download - from the ubuntu server.
Doing nothing with this modern kernel (K/Ubuntu use a 3.0-something-homebrew) the idle machine had a fan doing 4000 RPM - constantly - while the CPU sat at ~40 C. That is to say, the fan is not regulated (This was observed by the command "sensors" from the lm-sensors package. Modprobe the kernel module "coretemp" if you want to see more info from "sensors"). I can only presume it is an unintended consequence of two choices the kernel developers have made.
To 'revert' those kernel choices we must boot with the kernel parametres --> pcie_aspm=force i915.i915_enable_rc6=1 <-- OBS: Both the parametres must be present to get a working fan regulation.
The parametres deal with PCI Express Active State Power Management and Intels GPU driver. Why the fan is effected by such a double combo? Someone should ask the (probably ACPI) kernel developers about that. As a nice side-effect we also get a much improved battery run-time. That is actually where I stumbled upon the parametres, in discussions about power regressions with newer kernels.
Anyway, using this, a boot with "Integrated Graphics" gives even better thermals than Win7. I was idling at ~37 C and a 1850-2000 RPM fan. With "NVIDIA Optimus" there were short periods of 2000 RPM and long bouts of 3500 at ~45 C in the CPU.
/MTJ

Answer 1

UPDATE: I was a bit hasty with my comments about the USB ports. I've now actually _installed_ Kubuntu 11.10-final, and plugging in a simple USB mouse does not break fan regulation. Neither does the USB harddrive. BUT, the HD connection raises the temperature somewhere (hidden motherboard sensor?) and that is enough to kick the fan into its 4000 RPM state. Unplugging the HD and idle waiting, waiting... will eventually bring back the sane fan RPMs.
Btw, waiting seems to be the (ab?)normal name of the game in Linux. Win7P has a much quicker fan regulation. Here the fan ramps up its speed even with minimal workloads - like typing this message in Firefox, and it takes a looong time to fall back.
@ homeyclaus, Hi.
> I get nothing of the sort with a vanilla T420, all-intel graphics ...
Machine better at thermals probably (slightly thicker, no nvidia card to generate heat etc), and the BIOS is different from the "s" and "si" models. But constant 4000 RPM and fan noise with these models has been an ongoing saga even in Windows. See the massive "T420s Fan noise Issue" thread - takes a full day to read through it, and "T420 fan noise ?" at:
http://forums.lenovo.com/t5/T400-T500-and-newer-T-series/T420s-Fan-noise-Issue/td-p/443569
http://forums.lenovo.com/t5/T400-T500-and-newer-T-series/T420-Fan-noise/td-p/417971
Could be a number of things, but ultimately it is a job for the Lenovo BIOS hackers. The EC (embedded controller) is responsible for regulating the fan,  and the ThinkPads have a long history of being shipped with bad EC code. See the (not updated for newer models) thinkwiki page:
http://www.thinkwiki.org/wiki/Embedded_Controller_Firmware#Firmware_issues
> I did notice that my previous laptop with an NVidia GS8400 discrete chip did run the fan pretty high though.
You and me both ;-) On my previous machine (Acer) from 2005 I had to undervolt both the AMD-64 CPU and the NVidia GPU, install extra passive cooling - copper fins, plates and thread - and build an electro-'mechanic' manual fan regulator to get the noise down to a bearable level. But I had fun doing it as well...
> Are you running the NVidia closed-source X server?
Nope. Haven't gotten to experimenting with that part yet.
> How is the system handling the switch-over from discrete to integrated graphics?
Handling? Win7P greeted me with something like a 1024x768 screen before I could configure the Intel card. Once done, I saw no difference (except less system heat) from running in Optimus mode - I'm not a gamer or 3D artist. Linux desktop works fine with its OpenGL effects when I set "Use VSync" to get rid of window tearing. I might never need to switch on NVidia again!
/MTJ