Maybe use local APIC interrupt handler for dealing with
PMC overflow on P6 and Athlon. However, Linux doesn't seem
to want to use the APIC unless an SMP kernel is built.

Improve user-level documentation. Add usage examples.

Implement a low-level PMC resource manager which doesn't
know about processes.

Generalize to other architectures. Start with UltraSPARC, since
that's what I have docs for.
