#!/usr/bin/stap # This script tries to identify contended user-space locks by hooking # into the futex system call. global FUTEX_WAIT = 0 /*, FUTEX_WAKE = 1 */ global FUTEX_PRIVATE_FLAG = 128 /* linux 2.6.22+ */ global FUTEX_CLOCK_REALTIME = 256 /* linux 2.6.29+ */ global lock_waits # long-lived stats on (tid,lock) blockage elapsed time global process_names # long-lived pid-to-execname mapping probe syscall.futex.return { if (($op & ~(FUTEX_PRIVATE_FLAG|FUTEX_CLOCK_REALTIME)) != FUTEX_WAIT) next process_names[pid()] = execname() elapsed = gettimeofday_us() - @entry(gettimeofday_us()) lock_waits[pid(), $uaddr] <<< elapsed } probe end { foreach ([pid+, lock] in lock_waits) printf ("%s[%d] lock %p contended %d times, %d avg us\n", process_names[pid], pid, lock, @count(lock_waits[pid,lock]), @avg(lock_waits[pid,lock])) }