doesn't advance while we're waiting on the lock. In fact, try to take
the lock even before blocking interrupts: the lock is locking "lasttime"
against other callers of cc_microtime(), not against the clock routines,
and if we take a clock interrupt while waiting for the lock, that's one
we don't have to take after the computations, but before returning to
the caller, and that makes the data a little fresher to the caller.
Moreover, inverting the order of splXXX() and simple_lock() permits us
to unblock interrupts before doing the long division.
With this, finally, performance of "ntpd" on my MP i386 seems to be no
worse than on non-MP i386, so this may fix PR kern/24207.
overloading "usec". The counter isn't counting micro-seconds, and using
the same variable to mean two different things is false economy: with
this change, the compiled object is 72 bytes smaller on i386, and the
code is easier to understand, to boot.
so that it doesn't fire when called twice in the same microsecond,
which can lead to large error accumulation.
Appears to fix "repeated gettimeofday() goes backwards" on a fast
alpha and i386 box.
This is derived from alpha/microtime.c and i386/tsc_microtime.c,
and will share with both ports.
This should fix PR port-sparc64/18452.
(approved by martin)
