Haven't finished (hardly started) the arch code for this yet (and probably
broke ppc64), so it is just an RFC at this stage.

The large CC list is because it is a reasonably big change, so I hope one
or two of you smart guys can see if it looks sound before I try to tackle
the rest of the arch code and start asking for testers.

This actually improves performance noticably (ie. a % or so) on schedule /
wakeup happy benchmarks (tbench, on a dual Xeon with HT using mwait idle).

-- 
SUSE Labs, Novell Inc.