Re: Customizing fan behaviour (temperatures)

[Lucas Levrel <lucas.levrel@u-pec.fr>]

Le 13 juillet 2016, Lucas Levrel a écrit :

> Hi,
>
> I would like to adjust the temperature at which the fan starts, because as it 
> is now it runs continuously, at low speed but this continuous noise bothers 
> me. I'd rather have it spin faster and intermittently. This is an HP laptop.
>
> I've read much (mostly Q&A pages and list threads, regular documentation 
> seems to be scarce), and investigated the behaviour of files in 
> /sys/devices/virtual/thermal . From what I understand there's no bug, just 
> the temperature thresholds are not to my taste.
>
> More specifically, there are 7 cooling_device's (4 of type Fan, 2 Processor, 
> 1 LCD) and 5 thermal_zone's (the first 4 really are temperatures, the last is 
> the fan speed). thermal_zone0 controls the fan. The lowest trip_point_?_temp 
> (?==4) is 45000, which is very low. Basically, after a few minutes of idle 
> operation temp reaches 50000 or 55000 (looks like there is 5 °C granularity) 
> and never gets lower: I've tried and manually set the fan to speed 2 (echo 1 
>> cooling_device2/cur_state), even then temp doesn't decrease below 50000.
>
> trip_point_?_temp are not writable. I've set thermal.act=60000 in the kernel 
> command line, to no avail; is this supposed to be reflected in the 
> trip_point_?_temp files? (Note: trip_point_[1-4]_type is "active".) This is 
> kernel 3.2.71 .
>
> What can you advise me to do now?
>
> And by the way, for my education:
> - how are the trip_point values determined?
> - how is hysteresis implemented? I mean, you don't want your fan speed to 
> change every other second, so the "speed up" threshold has to be higher than 
> the "speed down" one. In fact, I've found no explanation of how the 
> trip_point values are used.
>
> Thanks.

Hi again,

After investigating some more, I found how hysteresis works: the 
trip_point_?_temp changes when it is crossed. In my case, 
trip_point_4_temp is 50000 at first (by default), and goes down to 45000 
when the fan starts.

This is also why I saw no effect of thermal.act=60000 last time I tested: 
during boot the temperature reaches this threshold, and trip_point_4_temp 
is set to 45000.

I remain with the following questions:
- how are the trip_point values determined?
- is there a way to set them to taste? More specifically, I would like to 
rise the "fan stop" trigger temp; thermal.act= visibly didn't change 
this...

Thanks again.

-- 
Lucas Levrel
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