Manual Pages  — LOCK_PROFILING

The LOCK_PROFILING kernel option also adds the following sysctl(8) variables to control and monitor the profiling code:

debug.lock.prof.enable
	Enable or disable the lock profiling code. This defaults to 0 (off).
debug.lock.prof.reset
	Reset the current lock profiling buffers.
debug.lock.prof.stats
	The actual profiling statistics in plain text. The columns are as follows, from left to right:

max
	The longest continuous hold time in microseconds.
wait_max
	The longest continuous wait time in microseconds.
total
	The total (accumulated) hold time in microseconds.
wait_total
	The total (accumulated) wait time in microseconds.
count
	The total number of acquisitions.
avg
	The average hold time in microseconds, derived from the total hold time and the number of acquisitions.
wait_avg
	The average wait time in microseconds, derived from the total wait time and the number of acquisitions.
cnt_hold
	The number of times the lock was held and another thread attempted to acquire the lock.
cnt_lock
	The number of times the lock was already held when this point was reached.
name
	The name of the acquisition point, derived from the source file name and line number, followed by the name of the lock in parentheses.

debug.lock.prof.rejected
	The number of acquisition points that were ignored after the table filled up.
debug.lock.prof.skipspin
	Disable or enable the lock profiling code for the spin locks. This defaults to 0 (do profiling for the spin locks).
debug.lock.prof.skipcount
	Do sampling approximately every N lock acquisitions.

Measurements are made and stored in nanoseconds using nanotime(9), (on architectures without a synchronized TSC) but are presented in microseconds. This should still be sufficient for the locks one would be most interested in profiling (those that are held long and/or acquired often).

LOCK_PROFILING should generally not be used in combination with other debugging options, as the results may be strongly affected by interactions between the features. In particular, LOCK_PROFILING will report higher than normal uma(9) lock contention when run with INVARIANTS due to extra locking that occurs when INVARIANTS is present; likewise, using it in combination with WITNESS will lead to much higher lock hold times and contention in profiling output.