following sysctl variables:
debug.mutex.prof.enable enable / disable profiling
debug.mutex.prof.acquisitions number of mutex acquisitions recorded
debug.mutex.prof.records number of acquisition points recorded
debug.mutex.prof.maxrecords max number of acquisition points
debug.mutex.prof.rejected number of rejections (due to full table)
debug.mutex.prof.hashsize hash size
debug.mutex.prof.collisions number of hash collisions
debug.mutex.prof.stats profiling statistics
The code records four numbers for each acquisition point (identified by
source file name and line number): longest time held, total time held,
number of non-recursive acquisitions, average time held. The measurements
are in clock cycles (as returned by get_cyclecount(9)); this may cause
measurements on some SMP systems to be unreliable. This can probably be
worked around by replacing get_cyclecount(9) by some incarnation of
nanotime(9).
This work was derived from initial patches by eivind.
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