Call for testers, significant sched_lock patch.

[Jeff Roberson]

I am going to commit a patch that goes significantly towards decomposing 
the scheduler lock into per-cpu scheduler locks.  Before this, I would 
like it if a few more people would run it under more circumstances than I 
have.  The patch is available at:

http://people.freebsd.org/~jeff/threadlock.diff

So far Kris Kennaway and myself have tested it fairly thoroughly on amd64 
machines with 1-8 processors.  We've mainly done various benchmarks as 
well as Peter Holm's stress2 suite.  It has survived our testing so this 
isn't totally unstable code.  I would like it if more people would test 
on any other architecture you have available.  I have also tested with 
4BSD and ULE with and without INVARIANTS and WITNESS.

This patch should have 0 or almost 0 effect on performance.  It sets the 
stage for a drop-in replacement for ULE that has per-cpu run queue locks. 
That scheduler has a sometimes dramatic effect on performance, depending 
on the workload.  I'm mostly looking for regressions here and not any 
particular perf impact.

Any questions on the design of the approach should be directed at the 
arch@ topics on the subject.

Thanks,
Jeff