I am on Slackware 14.2 and my laptop is Dell XPS 15 9550. After the latest system update, the kernel was updated from 4.4.14 to 4.4.38. This resulted in problems with the fan:
1. It is constantly ON - this was not the behavior before
2. It makes a high pitched noise which is causing me headaches
Any ideas how I can fix this. I am using the generic kernel with an initrd.

I've never used fancontrol but I think it might be a place to start.

https://linux.die.net/man/8/fancontrol

https://sourceforge.net/projects/fancon/

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

There is a script you can use with lm_sensors:
http://www.linuxquestions.org/questi...-a-4175495789/

HTH

Thanks for the help! I tried both i8kutils and fancontrol and was able to stop the fans. It turned out however, that the high-pitched noise which causes me headaches is not from the fans, because it continued even after the fans were off. I suspect it is coil whine. Any idea why a kernel update would cause that?

ouch.
my machine's psu has coil whine and it starts right after i press the power button - can you confirm that?

other than that, my first thought was that your system might be under higher load after the update. maybe because some graphics driver broke and hardware accel isn't available anymore.

I use bumblebee and keep my nvidia graphics card constantly off. I use the intel graphics for the X server but I have not noticed any slower performance since the update. The whine indeed starts with the power button and it is there even if I go to the BIOS instead of booting into linux. However, the pitch is different from when I am booted into linux, so I guess that the kernel has some influence over it and it is not a purely hardware problem.

Also the whine is definitely worse if I plug the laptop into the AC power compared to when I use it on battery.

You're Welcome.

I don't recommend keeping the fan turned off for long.
You wouldn't want the CPU to get too hot.

Maybe this coil whine article will be a help?

https://linustechtips.com/main/topic...rd-coil-whine/

When you get a chance open the case and take a good look at the mobo.
Make sure the wire to the fan isn't hanging to touching the board or anything else isn't touching were it shouldn't.

my experience is the same, and i think it's about different currents required at different times, not about software as such.
also see the article linked above - it still might have something to do with the graphics, indirectly (wild idea: kernel update enables better onboard gpu drivers, rersults in more or less current required at different times).

i came to the conclusion that coil whine in a PSU is harmless (albeit extremely annoying).

however, mine is a desktop, not laptop (sorry i missed that before).
typically, your psu is something that isn't even inside the laptop, no? so if the whine comes from inside the laptop, it's probably something more serious.

edit:
the forum thread linked above says something about GPU coil whine - that could apply to your situation.

Thanks for your help!

The PSU is indeed not inside the laptop, but it also has a bit of a coil whine. However, the laptop's coil whine is bigger. I feel like the laptop's coil whine increased a bit over the last couple of days, but I might be wrong - it is hard to tell.

I guess it is related a lot to some power management settings, since the whine comes from the area of the power input port. And indeed, after unplugging the power, coil whine almost disappears. So my guess is that when it switches from AC power to battery, some component gets limited in its performance settings and that's why the coil whine stops. I have no idea how to debug this further though.

I opened the laptop and everything inside seemed fine. In any way, I don't think it is a hardware issue: I booted the 4.4.14 kernel from my installation USB stick and the coil whine was not there. Indeed, not the same modules would have been loaded and the power load would not be the same, but I guess it is some basis for comparison since the whine is there with the 4.4.38 kernel, even before I start X.

In terms of the intel GPU theory, I checked the changelog of the update, and no intel-related drivers were updated. But I guess it still can it be caused only by a change inside the kernel? Do you know how can I limit the FPS of the intel graphics so I can test if the coil whine disappears. I have been trying to figure that out, but cannot find anything helpful.

Another update: This might actually be a hardware issue. I reinstalled the old kernel, but the coil whine is there. Can this be because of some library / package update? The whine is there even before I start X. Or is it definitely a hardware issue?

all i can say is, if it is coil whine, then it's a hardware issue.
it can be affected by software, but don't let that lead you to believe that you can fix it with software.

on my desktop, i've been planning to drown the affected coils in hot glue, i read somewhere that it might help. if you understand the physicality of the process, it makes sense.

A few weeks ago I installed Gentoo on an XPS 13 (2nd gen).
During the installation I heard all the time some noise like coil whine - I especially suspected some kind of coil whine because the noise was disappearing every time I was using at least 1 cpu 100%.
The noise disappeared once I activated the correct audio modules in the kernel (which I initially forgot...) => the weird noise came therefore from the speakers.

ondoho, I have heard that varnish also helps. I still have difficulty locating the problematic coils though. Here is a picture I took when I opened the laptop: https://ibb.co/dfd7bQ . I cannot see any coils though...

Pearlseattle, this sounds interesting. Do you remember from which area of the laptop the whine was comping from? Mine is coming from around the power cable input. Also what are the audio modules that you use and how did you determine they are the correct ones?

if you look at the puictures i linked you will notice there's also something called "capacitor squeal".

but i've never heard of anyone having that on a laptop, sorry.

you're going to have to trust your ears to identify where that sound actually comes from.

I think that it was an incredibly stupid mistake (something like selecting everything excluding the intel hd audio) but I don't remember anymore and cannot check as I have borrowed the laptop to a friend. But I remember that in the end I just selected all audio drivers as modules, rebooted, and the noise was gone (was teaching the installation of Gentoo to a friend and after two weeks of working on it we were both relieved of not having to hear that anymore - at the beginning he did not notice the noise but as soon as I made him aware of that he couldn't stop hearing it, hehe...).
Basically the noise disappeared as soon as we were able to play an audio file with "mpv myaudio.mp3" without any options (meaning that the correct audio device was being picked up by default).
If I remember correctly the noise was coming from the upper-right part of the laptop.