- Fetch the root set from cpuset_getaffinity() instead of assuming all CPUs
from 0 to hw.ncpu are the root set.
- Use CPU_SETSIZE and CPU_FFS.
- The original notion of halted CPUs the manpage and code refers to is gone.
Use the term "available" instead.
Differential Revision: https://reviews.freebsd.org/D2491
Reviewed by: emaste
MFC after: 1 week
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