Call for testers, amd64 only, new scheduler.

[Jeff Roberson]

This is actually a ULE derivative that I have been discussing for some 
time.  It is now stable enough that I would like more people to bang on it 
and give feedback about performance and tell me about any stability 
problems they encounter.

You can see in the following graph that the ramp-up times for the sysbench 
benchmark have improved although the tail has suffered a little:

http://people.freebsd.org/~jeff/sysbench.png

The new scheduler is FreeBSD-7.0-ULE-pcpulocks.  On my dual cpu system the 
results are much less ambiguous.  It's a 10-15% win on sysbench across the 
board.  This also improves an artificial thread benchmark included with 
sysbench by 500% on an 8 way and gives us ebizzy numbers on par with or 
better than linux.

It also includes a mechanism that should improve bde's nfs buildworld 
times, although I have not yet verified that.  Hopefully he'll try it as 
well.  It should reduce CPU idle time while also negating the effects of 
thrashing other cpus run queues in the idle thread.

The new patch is at: http://people.freebsd.org/~jeff/schedsmp.diff

You have to change your scheduler to SCHED_SMP.  x86 support is 
forthcoming.  Depending on feedback and what re thinks I am going to 
consider replacing ULE entirely with SCHED_SMP or committing this as a 
seperate scheduler for 7.0.

Thanks,
Jeff