This has so far been ported to and tested on i386, x86_64,
ppc64, ia64. I've done an untested hack for sparc64 too.

Unfortunately the change will have to touch all architectures,
but fortunately the above ones are among the more complex.

This patch improves cross CPU rescheduling performance, and
idle reschedule performance by a significant amount on the
systems I've tested on (SMP G5, quad McKinley, SMP+HT P4 Xeon)
in microbenchmarks.

I bet it could give a measurable boost on real workloads on
some systems too. And I think it is a good cleanup in general.

Comments?

-- 
SUSE Labs, Novell Inc.