I have an old thin client that I upgraded to a home server by adding some additional RAM and storage. I noticed after a recent kernel upgrade that the system seemed sluggish at times, despite doing nothing in particular at the time.
top showed that a kworker process was using CPU, not all of it, but perhaps 25 to 50% of the total CPU.
I did a lot of searching to try and track down the offender. I used tools such as perf and iotop, read about various tunables under /proc related to power management. Finally, I ran Intel’s powertop command. It showed that “Audio codec alsa…” was hammering on some event loop.
I looked at the loaded kernel modules, and on a whim, I did
sudo rmmod snd_hda_intel and that fixed the issue for me.
Others may find that a kworker is running in a tight loop for some other reason. It could be some other misbehaving driver or an I/O problem.