kernel_task consumes 500% CPU on AC power, sometimes [duplicate]

Solution 1:

In my experience this has always been due to a hardware fault. However before doing anything else reset the SMC as detailed here: http://support.apple.com/kb/HT3964 as its power related.

This appears to happen when the Mac is struggling to communicate with hardware. Which Mac is it? How old is the battery? Is your battery life still good? Has the Mac had any damage - dropped? Liquid? Have you tried a different power adapter?

Solution 2:

I got this issue once on my 15-inch Mid 2012 MBP running 10.8.4 because the audio input had switched to the internal microphone and it was picking up the constant noise of my fan. Switched the audio input to Line In and cpu usage dropped from 524% to 3%

Solution 3:

http://www.rdoxenham.com/?p=259 covers disabling the kernel extension responsible for triggering this misbehavior. However, doing so also disables some other thermal management functionality.

Solution 4:

The folks who observed "AC power" contributes are on to something.

High chassis temperature from charging together with peripherals plugged in can cause this issue. Simply moving the charging cable from the left to the right ports can be enough to cool the hotspot and resolve the problem. On a machine with MagSafe try unplugging peripherals from the left ports until the battery is full.

CPU usage has nothing to do with this. A hot CPU is throttled by reducing its clockspeed not by scheduling no-op load.

See https://apple.stackexchange.com/a/363933/27135 for causal proof.