It’s hot, you’re hot, and your Mac’s slowed right down. Wondering what’s holding it, and you, up, you open Activity Monitor. There it is at the top of the process list in its CPU tab: kernel_task. No wonder you can’t get anything done, macOS is on the blink again.
Except it probably isn’t: macOS is most likely doing its job very well, and ensuring that your CPU doesn’t overheat like you.
Macs have several temperature sensors, and a whole sub-system (Core Duet) devoted to managing the internal environment and services. When your Mac is trying to run processes which are CPU-intensive and its internal temperatures start to rise as a result, its cooling systems like fans kick in, and the demand being placed on the CPU is eased off. That may involve dropping CPU speed, where that is available, and occupying it with another process – and that’s what kernel_task is probably doing.
So seeing kernel_task taking high percentages of CPU isn’t a useful sign of impending catastrophe, such as a kernel panic, although there are time when it can be. It’s just your Mac’s way of controlling the availability of the CPU when it’s getting a bit thermally stressed. It’s time to close Activity Monitor, and give yourself and your Mac a chance to cool down.
If this sounds too good to be true, here’s Apple’s note on it.
You can find further information on dealing with these problems in this article.
Thanks to @mikeymikey for reminding us of this.