Dell Precision T3600 dirty PWM fancontrol
Well it is not real PWM, rather dirty implementation to achieve optimal-ish cooling, somewhere between quiet & hot and full speed jet engine sound barrier.
I'am running T3600 with Intel(R) Xeon(R) CPU E5-2665 (8 core) as my home lab / server. To gain WAF, I had to quiet it down. Since BIOS does crappy job keeping machine cool / quiet, I had to improvise.
Run it periodically, just put this in your cron, and it should do the rest. You might need to install python-psutil package using pip or your OS package manager.
I've noticed that CPU fan has two states - full speed and idle speed, nothing in between. I've managed to calculate pseudo-PWM value which is related to CPU & ambient temp, so it now regulates fan speed between idle/full constantly, allowing fan to spin at middle speeds. This pseudo-PWM works only when CPU temp is between LOW_LIMIT and HIGH_LIMIT. Feel free to change it to your needs in pwm.py.
T3600 has three front fans - top and middle can be controlled by PWM, third spins at constant speed, we won't talk about this one. Other two can be controlled between idle speed (~800 RPM), low speed (~1200 RPM) and high speed (~4000+ RPM).
fan_control.py logic is to increase front fans first when CPU temp rises, if that won't help, pwm.py which controls CPU fan speed should do the job and if CPU still getting hot, full speed mode should activate when temperature reaches ~70 C.
My temperatures and RPM at idle:
load average: 3,38, 3,37, 3,62
Processor Fan: 1611 RPM
Other Fan: 766 RPM
Other Fan: 2000 RPM
CPU: +46.0°C
Ambient: +21.0°C
P.S: I've commented out middle fan (PWM3). I've left medium fan speed in BIOS and this setting keeps middle fan at ~2k RPM constantly without much noise.