Arch Linux

luca4arch

Member

Registered: 2015-04-05

Posts: 4

fan control in notebooks

Hi all,
I am using Arch Linux since a few months, right after purchasing my new laptop, a Dell Precision M3800. Anyway I am a linux user since many years. I like very much the control that arch give to the user in terms of configuration possibility. My question is relate to fan control in notebooks. Even though I noticed this issue in my laptop now, I think similar observation holds also for other notebooks and linux distros. For fan control I use the fancontrol utility. Once properly configured, there is a min temperature value below which the cpu fan is off (default is 20 °C, I increased up to 45 °C) and a max temperature value (default is 55 °C and I placed 65 °C) above which the fan is running at full speed. The reason for the temperature limit changes is to emulate windows behavior in terms of noise and thermal handling. With a room temperature in the order of 25 °C, I get right after login a cpu temperature of about 35 °C. Then the temperature increases even in idle conditions up to the limit of 45 °C and then it is stabilized by the cpu fan. Chaning the temperature between 35 °C and 45 °C simply changes the time interval I have to wait until the cpu fan switches on and cpu temperature stabilizes with low load. The point is the the stable thermal situation produces a continuous switching of the fan state, let's say the fan is on for a few seconds every minute. The reason is that the fan switches off right after the cpu temperature falls below the value for which it turns on. Wouldn't be better to define two different temperatures for switching on and off? Let's say, fan on when temperature reaches 45 °C and off when it falls below 40 °C. Is there a way to do that with fancontrol or same other tool?
Thank you in advance.
Bye,
Luca

Head_on_a_Stick

Member

From: The Wirral

Registered: 2014-02-20

Posts: 9,003

Website

Re: fan control in notebooks

Is your return key broken?

https://wiki.archlinux.org/index.php/Fan_speed_control

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Jin, Jîyan, Azadî

luca4arch

Member

Registered: 2015-04-05

Posts: 4

Re: fan control in notebooks

Yes, it works
But the wiki link does not answer to my question (I checked it before posting as well as fancontrol man pages, of course)

mwillems

Member

Registered: 2014-08-09

Posts: 93

Re: fan control in notebooks

OP, what you're describing is called (at least in HVAC circles) hysteresis.  You may be able to find some fan control scripts that support it (googling fan control + hysteresis), or just write one yourself.  You can also control this behavior to some extent by adjusting fancontrol's polling behavior (the "INTERVAL" setting), but that has risks. 

I think implementing hysteresis is not a particularly useful endeavor because PC temperatures can change 30 degrees or more in a few seconds when under load, which is completely unlike, say, a home thermostat where temp changes are much more gradual over time.  Realistically, you should expect to always be running at least the CPU fan at some speed, and set your "turn off" temperature for it to room temperature.  You can set different temperature set points for different fans, so you can have the CPU fan turning off at a lower temp, but have other fans off until the temp gets much higher.

Last edited by mwillems (2015-05-31 16:35:48)