cpuset and affinity implementation

[Jeff Roberson]

Please see:
http://people.freebsd.org/~jeff/cpuset.diff

This is unfortunately intertwined with ULE's new CPU selection algorithm 
so that code is in the patch as well.  Otherwise, this includes a simple, 
ugly userland tool called cpuset and all of the kernel support required. 
I have tested this by creating sets and subsets and modifying their cpu 
masks under load.  I'm able to dynamically reprovision without issue.

This doesn't have support for jails but the infrastructure is there.  It 
also fails to modify sets if it would leave threads without a valid cpu 
to run on.  I have not implemented a force option but it will be trivial 
to do so.  The initial cpu set is also created before we know all_cpus so 
it's faked up with all cpus set for now.

I mostly want people to look at the interface in cpuset.h and make sure 
they agree with it before I start polishing to commit.  I'm fairly happy 
with the way the syscall api looks now.  The code itself ended up being 
much more complicated than I'd hoped due to locking considerations.  Try 
not to look at cpuset_setproc() ;).

If you want to actually try the patch, here's a couple of neat things to 
do with cpuset:

cpuset -l 0-4 /bin/sh

This creates a new group with a list (-l) of cpus 0-4 inclusive and runs 
sh in it.

cpuset -g -p <sh pid>

This will get (-g) the mask of cpus pid (-p) is allowed to run on.

cpuset -l 0,2 -p <sh pid>

This will restrict sh to running on cpus 0, 2 while its group is still 
allowed 0-4.

cpuset -l 0,2 -c -p <sh pid>

This will modify the cpuset (-c) that the sh belongs to.

cpuset -l 0-3 -s 1

This will modify the set (-s) that all threads are in by default to 
contain the first 4 cpus leaving the rest idled.

Feedback is appreciated.

Thanks,
Jeff