uprobe:$MMTK:_ZN3std3sys4unix5locks11futex_mutex5Mutex14lock_contended* {
    if (@stats_enabled) {
        @lock_nsecs[tid] = (arg0, nsecs);
    }
}

uretprobe:$MMTK:_ZN3std3sys4unix5locks11futex_mutex5Mutex14lock_contended* {
    if (@stats_enabled) {
        @lock_dist[@lock_nsecs[tid].0] = hist((nsecs - @lock_nsecs[tid].1)/256);
    }
}