MP machines (hopefully). CPU timers are OK on UP machines but we
don't keep the timers in sync on MP machines so if the CPU's timer
is chosen as the primary timecounter it's possible for time to
not be monotonically increasing because different CPU's counters
may be used at different times. But the CPU's counters are otherwise
one of the higher quality counters available. So, on UP machines
we'll use a relatively high quality value but on MP machines we'll
use a quality that should prevent the CPU's counters from being chosen.
Requested by: green (who did the first version of the patch)
Reviewed by: marius, green
MFC after: 1 week
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