Cpu hotplugging breaks CPU usage scale

This is similar to having an IO spike that dwarfs all the other peaks,
until the spike disappears from view.

However it makes no sense here, as a CPU core could never have used
more than 100%.

That's what it looks like, all cores are going 100%, the affected one
had just gone online after a period of sleep:

http://s21.postimg.org/3qjmqoo6f/hotplug_weird.jpg