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I have a 15" Mid 2012 Retina MacBook Pro (2.7ghz i7, 16gb of RAM) that I use as a headless server in my house. It's currently running 10.15.7, which is the last supported MacOS release it can run.

When I leave the machine running, screen open but brightness all the way down, the fan CONSTANTLY runs. As soon as I turn the brightness up and start using the computer, or remote in with a VNC client (I'm using the one that's an extension for chrome) the fan stops running. Looking at Activity monitor, there's a kernel_task that using around 15% of the CPU that immediately stops when I remote in or start using the computer. You can see the task and drop in CPU usage in the attached screenshot (screenshot taken after the %CPU has dropped, but you can see kernel_task, and the associated load on the graph at the bottom).

I've done a clean install of 10.15.7, and the only programs I have installed are: Chrome, Docker, pi-hole running in Docker, and Homebridge (for homekit).

I thought it might just be spotlight re-indexing the computer, but it's been about a week and the problem hasn't gone away. I have tried a SMC and PRAM reset, and neither have helped. It's pretty much running a clean install, other than the programs I have listed.

Does anyone have any tips for figuring out what is causing kernel_task to use the CPU so often? Why does it go away when I start using the computer?

enter image description here

mrhomer
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  • Does this answer your question? Why is kernel_task using so much CPU? – Lulucmy Feb 26 '21 at 22:35
  • Neither of these seem to be similar issues to mine. The CPU isn't ramping up above 100%, and it isn't related to temperature, and it isn't throttling. Still, I have read these threads, and pretty much anything else about kernel_task that I can find, and I've tried the solutions they recommend. I'm mostly wondering if there are any tools to diagnose what kernel_task is doing. – mrhomer Feb 27 '21 at 02:06
  • Or, I guess I should say "I don't think it's related to temperature". The computer isn't hot at all when I use it, and the fan doesn't run. If I let it sit for an hour, unused, I come back and the CPU is at 15%, the fan is running, and it's warm. If I leave it sitting, open, and jiggle the mouse every 10 min it never ramps up or gets warm. – mrhomer Feb 27 '21 at 02:11

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