T2 fan control on Linux (trying to understand the basics)

[Boyd01]

Just installed AlmaLinux on a 2018 Mac Mini and repeated searches didn't find much about others using it (booting into AlmaLinux, not using a VM). But it works and seems great. There's no indication that this version of Linux has any support for the T2 chip. I'm aware of the versions at t2linux, but have a reason to use AlmaLinux instead. Have also read about various software like t2fanrd, mbpfan and others but installation appears to be rather involved.

Really, I'm just trying to understand the issue and whether I should even be concerned about fan control. Most of the other t2-related issues are for things like laptop keyboards, trackpads, bluetooth, wifi, etc. and I just don't care about those on a Mini which will only be used as a server. But, of course, I don't want to fry my Mac. 🙂

Assuming that we don't install any special software, exactly how does fan control work on a t2 Mac? Does the t2 chip independently control that based on its sensors, regardless of operating system? Are these fan control packages just for cases where that built-in system doesn't produce the desired results? I'm using cockpit and it shows CPU temperature - I think that coretemp is installed, but not not applesmc. Here's an example where the temperature got hot (just from opening the statistics in cockpit, actually)

The fans ramped up as soon as that happened, so something is obviously working automatically. Just sitting idle, the temperature is usually in the 60-70c degree range. The fans only ran on high for a very brief time and the temperature dropped quickly afterwards. It bounced around a bit, but then stabilized as usual, which suggests that I'm OK. This is what it showed about a minute after the first screenshot, shortly after the fans slowed down.

I'll just keep an eye on this over the coming days to get some sense of whether there's a problem. Have never seen the temperature spike above 100c yet, and it always drops quickly. I suppose there could be an issue when the server is under heavy load, but I don't expect that too often. I'm using this for web app development, so it's mostly just serving http over my LAN which should be an easy lift. The most intense cpu load (so far) has been zipping/unzipping some big files (up to 300gb).

TL;DR... should I be worried about frying my 2018 t2 Mini while using it as a server?

 

[Paddy OPlastic]

I don't have experience of T2 machines but the processor temperature will climb quickly under load and the i7 goes up to around 100C before starting to throttle. I'd say the default fan parameters look like they're doing the job.

 

[Boyd01]

Thanks. I also have the same AlmaLinux installation running on a 2012 quad i7 Mini, which doesn't have a T2 chip. Would there be any reason to expect the fan to behave differently on that machine? How about a PC or a rack server? Sorry for my ignorance, but are fans normally controlled by device firmware, or does Linux monitor temperatures and control fans?

 

[Paddy OPlastic]

Thanks. I also have the same AlmaLinux installation running on a 2012 quad i7 Mini, which doesn't have a T2 chip. Would there be any reason to expect the fan to behave differently on that machine? How about a PC or a rack server? Sorry for my ignorance, but are fans normally controlled by device firmware, or does Linux monitor temperatures and control fans?

If you don't install anything specific, or don't tell the OS to do anything differently, the OS will rely on the thermal parameters programmed into the microcontroller. The T2 is similar to any other microcontroller for a PC-type system in this respect.

 

[Boyd01]

Thanks, that makes sense. So - as I understand it - software packages like mbpfan and t2fanrd are for users who aren't satisfied with the default fan response? With a laptop, you might be annoyed by roaring fans or if it's unpleasantly hot on your lap. But that's more of a personal preference instead of something which could damage the computer?

I know that people also use fan control apps on MacOS, and have complained about how hot the Intel Mini's get. I've had quite a few, and they do get hot running MacOS. I never felt they were getting hot enough to be a problem though and never installed any special software on MacOS (my one problem turned out to be cat hair clogging the air intake 😹).

Anyway, the default seems to be ramping the fans way up when the CPU gets around 100c, thenthey slow back down as needed. Even when temperature is low, I can hear a very soft mechanical noise if I listen carefully and can feel a gentle stream of warm air blowing out. Will continue to just observe what happens, maybe try some stress-testing. But would also be interested to hear if others have actually had problems with overheating CPU's on Linux, especially the 2012 and 2018 Mini.

 

[Boyd01]

I found this program which looks like a great way to monitor the sensors and attempt to understand what's going on. Since coretemp was already installed, setting it up was trivial.

https://www.cyberciti.biz/faq/howto-linux-get-sensors-information/

It interactively walks you through a scan of all available sensors, which ended like this on my 2018 Mini:

Now follows a summary of the probes I have just done.
   Just press ENTER to continue:
          Driver `coretemp':
          * Chip `Intel digital thermal sensor' (confidence: 9)

Following this, simply typing "sensors" produces this output

pch_cannonlake-virtual-0
Adapter: Virtual device
temp1:        +60.0°C
coretemp-isa-0000
Adapter: ISA adapter
Package id 0:  +48.0°C  (high = +100.0°C, crit = +100.0°C)

Core 0:        +46.0°C  (high = +100.0°C, crit = +100.0°C)
Core 1:        +46.0°C  (high = +100.0°C, crit = +100.0°C)
Core 2:        +43.0°C  (high = +100.0°C, crit = +100.0°C)
Core 3:        +44.0°C  (high = +100.0°C, crit = +100.0°C)
Core 4:        +44.0°C  (high = +100.0°C, crit = +100.0°C)
Core 5:        +44.0°C  (high = +100.0°C, crit = +100.0°C)

enp1s0-pci-0100
Adapter: PCI adapter
PHY Temperature:  +78.3°C
MAC Temperature:  +77.9°C

You can also run it continuously with with a command such as "watch -n2 -d sensors", which updates the values continuously and highlights the changes.

 

[Paddy OPlastic]

Thanks, that makes sense. So - as I understand it - software packages like mbpfan and t2fanrd are for users who aren't satisfied with the default fan response? With a laptop, you might be annoyed by roaring fans or if it's unpleasantly hot on your lap. But that's more of a personal preference instead of something which could damage the computer?

I know that people also use fan control apps on MacOS, and have complained about how hot the Intel Mini's get. I've had quite a few, and they do get hot running MacOS. I never felt they were getting hot enough to be a problem though and never installed any special software on MacOS (my one problem turned out to be cat hair clogging the air intake 😹).

Anyway, the default seems to be ramping the fans way up when the CPU gets around 100c, thenthey slow back down as needed. Even when temperature is low, I can hear a very soft mechanical noise if I listen carefully and can feel a gentle stream of warm air blowing out. Will continue to just observe what happens, maybe try some stress-testing. But would also be interested to hear if others have actually had problems with overheating CPU's on Linux, especially the 2012 and 2018 Mini.

Laptops and small form factor PCs/Macs don't have a lot of room for large heatsinks to absorb and dissipate the heat so they must react quickly to rises in temperature. If your Mini is ramping up the fan speed quickly enough to keep the temperature from going above 100C then all is good. For all machine types things like thermal paste degradation (and cat hair) can cause overheating and might prompt people to use applications to modify the default cooling profile. That's why I wrote something specific for my iMac 10,1 under Linux; regardless of the HDD fan issue (which I could have just set to a constant value) it would run very hot, worryingly hot in fact. When I had macOS on it I ran the fan app from Crystalidea to keep it cooler than the default. I suppose I should really take it apart and replace the thermal paste but, um, you know, things and stuff.

 

[Boyd01]

Tried a little stress testing on the 2018 Mini while watching temperatures and it was pretty interesting. Simultaneously tried multiple file transfers, zip files and heavy access of the web server. The mini didn't even break into a sweat. But I could hear the fan quietly running if I put my ear right next to the mini and could feel a gentle warm exhaust, so the fans were definitely running.

Then I opened the cockpit web console and went to the system metrics, which was a big load the last time I tried. That warmed things up.

Since I have no way to actually see fan speed, not sure, it seemed like the fans might have been running a little faster but they were still very quiet. When it finally hit 100c though, the fans started roaring at full speed.

FWIW, the CPU temperature shown in cockpit matches the "Package id 0" value in the sensors app.

The roaring fan seemed to do the job though. After just a few minutes the temperatures dropped way down and fan got pretty quiet. To be fair, the zip jobs also completed by then, but the other processes were still active.

Anyway, this gives me some confidence that the fan(s) are doing their job and my Mini won't get fried. I can see why someone might want to tweak this behavior though, to more gradually ramp fan speed up and down instead of the big transitions I heard. But, for a server, that doesn't matter much to me and the temperatures don't seem to be getting out of hand. For the most part, I won't be stressing it this hard either.