Photo by skeeze
Thanks to Howard Oakley for explaining something that has bothered me for years. When my iMac is struggling under a heavy CPU load, performance suffers, and I can hear its fans ramping up. Checking in Activity Monitor often reveals that a process called kernel_task is taking a large percentage of the CPU. I mutter something unprintable and hope that things resolve themselves soon, which they usually do, eventually. What the %$#*@^ could kernel_task be doing?
It turns out that kernel_task is actually stepping in to make the CPU less accessible to other processes that are taxing the CPU so intensely that they’re causing its temperature to reach dangerous levels. In other words, kernel_task is protecting your CPU from overheating, and not itself causing the problem. Once the CPU temperature drops, kernel_task automatically backs off so other processes can resume their activity.