From: Ingo Molnar <mingo@elte.hu>

This cleans up the NUMA scheduler to have separate triggers for idle
and busy rebalance ratio, preventing some complex interactions where
idle cpus can cause busy ones to busy rebalance more often. The core
functionality of this patch is rebalace_tick().

Tested in -mjb tree for over 1 month ... no problems at all found -
retested on top of 64-bk3 with new scheduler updates.