It is a cool trick, but it was a surprise to me that they go to such lengths to get a "busy" CPU to handle the timer expiration. I would have thought that you'd want to handle extra work like timer expiration with an idle CPU, since the busy CPU has (by definition) other work to do. OTOH you could also argue that timer expiration does not take a lot of time and so the slowdown would be negligible. The power savings might be worth more. If it does matter you could always pin code and timers to specific CPUs I guess.

This does seems to be one of the usecases that you would want to use the little cores in a big/little architecture for btw.