[PATCH] hwpmc(4) changes to use 'mp_maxid' instead of 'mp_ncpus'.

[Joseph Koshy]

>  We should take some care to make sure we don't over generalize.

hwpmc(4) today handles Intel P4 counters; those are moderately
complex in terms of architecture.

>  If nothing else, these counters could be even more useful on CPU-poor embedded
>  devices.

Conventional PMCs should be supportable without much ado.

Koshy