MacOS – Activity Monitor suddenly showing all cores in Dock icon

iotop would be the first place to go if Activity Monitor wasn't getting you an answer. It uses dtrace instead of the activitymonitord and has far superior probing skills without the "needing to learn DTrace" part.

Instruments would be my second choice but it has so many presets, it might be some probing until someone answers with an easy 1, 2, 3 to reveal the specific workload of FileVault 2.

There is a bug in Activity Monitor v10.8.0 (806). If you select Dock Icon > Show CPU History, is automatically closes the floating window and appears in the dock. If you attempt to switch back to the floating window, sometimes only one core appears.

Solution: - Close floating windows - Dock Icon > Show Memory Usage - Quit and Restart Activity Monitor - Dock Icon > Show Application Icon - Quit and Restart Activity Monitor - Monitors > Show CPU History

Now you should see all of your cores/vccores. :-)

This bug is not always reproducible, but I've experienced it before.