From: Nick Piggin <piggin@cyberone.com.au>

This patch gets the sched_domain scheduler working better WRT balancing.
Its been tested on the NUMAQ.  Among other things it changes to the way SMT
load calculation works so as not to active load blances when it shouldn't.

It still has a problem with SMT and NUMA: it will put a task on each
sibling in a node before moving tasks to another node.  It should probably
start moving tasks after each *physical* CPU is filled.

To fix, you need "how much CPU power in this domain?" At the moment we
approximate # runqueues == CPU power, and hack around it at the CPU
physical domain by counting all sibling runqueues as 1.

It isn't hard to correctly work the CPU power out, but once CPU hotplug is
in the equation it becomes much more hotplug events.  If anyone is actually
interested in getting this fixed, that is.