On: Ubuntu will switch from X window server to Mir

[mercurial]

That's curious. You might be a victim of this bug:

https://bugzilla.redhat.com/show_bug.cgi?id=813407

I'm not sure if this could affect the CPU usage. I hear that you can play with the resample setting to lower it, but I haven't had to do that on a 5+ yo desktop.