6 As the name suggests, it provides statistics on locks.
10 Because things like lock contention can severely impact performance.
14 Lockdep already has hooks in the lock functions and maps lock instances to
15 lock classes. We build on that (see Documentation/locking/lockdep-design.txt).
16 The graph below shows the relation between the lock functions and the various
39 lock, unlock - the regular lock functions
43 With these hooks we provide the following statistics:
45 con-bounces - number of lock contention that involved x-cpu data
46 contentions - number of lock acquisitions that had to wait
47 wait time min - shortest (non-0) time we ever had to wait for a lock
48 max - longest time we ever had to wait for a lock
49 total - total time we spend waiting on this lock
50 avg - average time spent waiting on this lock
51 acq-bounces - number of lock acquisitions that involved x-cpu data
52 acquisitions - number of times we took the lock
53 hold time min - shortest (non-0) time we ever held the lock
54 max - longest time we ever held the lock
55 total - total time this lock was held
56 avg - average time this lock was held
58 These numbers are gathered per lock class, per read/write state (when
61 It also tracks 4 contention points per class. A contention point is a call site
62 that had to wait on lock acquisition.
66 Lock statistics are enabled via CONFIG_LOCK_STAT.
70 Enable collection of statistics:
72 # echo 1 >/proc/sys/kernel/lock_stat
74 Disable collection of statistics:
76 # echo 0 >/proc/sys/kernel/lock_stat
78 Look at the current lock statistics:
80 ( line numbers not part of actual output, done for clarity in the explanation
83 # less /proc/lock_stat
85 01 lock_stat version 0.4
86 02-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
87 03 class name con-bounces contentions waittime-min waittime-max waittime-total waittime-avg acq-bounces acquisitions holdtime-min holdtime-max holdtime-total holdtime-avg
88 04-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
90 06 &mm->mmap_sem-W: 46 84 0.26 939.10 16371.53 194.90 47291 2922365 0.16 2220301.69 17464026916.32 5975.99
91 07 &mm->mmap_sem-R: 37 100 1.31 299502.61 325629.52 3256.30 212344 34316685 0.10 7744.91 95016910.20 2.77
93 09 &mm->mmap_sem 1 [<ffffffff811502a7>] khugepaged_scan_mm_slot+0x57/0x280
94 19 &mm->mmap_sem 96 [<ffffffff815351c4>] __do_page_fault+0x1d4/0x510
95 11 &mm->mmap_sem 34 [<ffffffff81113d77>] vm_mmap_pgoff+0x87/0xd0
96 12 &mm->mmap_sem 17 [<ffffffff81127e71>] vm_munmap+0x41/0x80
98 14 &mm->mmap_sem 1 [<ffffffff81046fda>] dup_mmap+0x2a/0x3f0
99 15 &mm->mmap_sem 60 [<ffffffff81129e29>] SyS_mprotect+0xe9/0x250
100 16 &mm->mmap_sem 41 [<ffffffff815351c4>] __do_page_fault+0x1d4/0x510
101 17 &mm->mmap_sem 68 [<ffffffff81113d77>] vm_mmap_pgoff+0x87/0xd0
103 19.............................................................................................................................................................................................................................
105 21 unix_table_lock: 110 112 0.21 49.24 163.91 1.46 21094 66312 0.12 624.42 31589.81 0.48
107 23 unix_table_lock 45 [<ffffffff8150ad8e>] unix_create1+0x16e/0x1b0
108 24 unix_table_lock 47 [<ffffffff8150b111>] unix_release_sock+0x31/0x250
109 25 unix_table_lock 15 [<ffffffff8150ca37>] unix_find_other+0x117/0x230
110 26 unix_table_lock 5 [<ffffffff8150a09f>] unix_autobind+0x11f/0x1b0
112 28 unix_table_lock 39 [<ffffffff8150b111>] unix_release_sock+0x31/0x250
113 29 unix_table_lock 49 [<ffffffff8150ad8e>] unix_create1+0x16e/0x1b0
114 30 unix_table_lock 20 [<ffffffff8150ca37>] unix_find_other+0x117/0x230
115 31 unix_table_lock 4 [<ffffffff8150a09f>] unix_autobind+0x11f/0x1b0
118 This excerpt shows the first two lock class statistics. Line 01 shows the
119 output version - each time the format changes this will be updated. Line 02-04
120 show the header with column descriptions. Lines 05-18 and 20-31 show the actual
121 statistics. These statistics come in two parts; the actual stats separated by a
122 short separator (line 08, 13) from the contention points.
124 Lines 09-12 show the first 4 recorded contention points (the code
125 which tries to get the lock) and lines 14-17 show the first 4 recorded
126 contended points (the lock holder). It is possible that the max
127 con-bounces point is missing in the statistics.
129 The first lock (05-18) is a read/write lock, and shows two lines above the
130 short separator. The contention points don't match the column descriptors,
131 they have two: contentions and [<IP>] symbol. The second set of contention
132 points are the points we're contending with.
134 The integer part of the time values is in us.
136 Dealing with nested locks, subclasses may appear:
138 32...........................................................................................................................................................................................................................
140 34 &rq->lock: 13128 13128 0.43 190.53 103881.26 7.91 97454 3453404 0.00 401.11 13224683.11 3.82
142 36 &rq->lock 645 [<ffffffff8103bfc4>] task_rq_lock+0x43/0x75
143 37 &rq->lock 297 [<ffffffff8104ba65>] try_to_wake_up+0x127/0x25a
144 38 &rq->lock 360 [<ffffffff8103c4c5>] select_task_rq_fair+0x1f0/0x74a
145 39 &rq->lock 428 [<ffffffff81045f98>] scheduler_tick+0x46/0x1fb
147 41 &rq->lock 77 [<ffffffff8103bfc4>] task_rq_lock+0x43/0x75
148 42 &rq->lock 174 [<ffffffff8104ba65>] try_to_wake_up+0x127/0x25a
149 43 &rq->lock 4715 [<ffffffff8103ed4b>] double_rq_lock+0x42/0x54
150 44 &rq->lock 893 [<ffffffff81340524>] schedule+0x157/0x7b8
152 46...........................................................................................................................................................................................................................
154 48 &rq->lock/1: 1526 11488 0.33 388.73 136294.31 11.86 21461 38404 0.00 37.93 109388.53 2.84
156 50 &rq->lock/1 11526 [<ffffffff8103ed58>] double_rq_lock+0x4f/0x54
158 52 &rq->lock/1 5645 [<ffffffff8103ed4b>] double_rq_lock+0x42/0x54
159 53 &rq->lock/1 1224 [<ffffffff81340524>] schedule+0x157/0x7b8
160 54 &rq->lock/1 4336 [<ffffffff8103ed58>] double_rq_lock+0x4f/0x54
161 55 &rq->lock/1 181 [<ffffffff8104ba65>] try_to_wake_up+0x127/0x25a
163 Line 48 shows statistics for the second subclass (/1) of &rq->lock class
164 (subclass starts from 0), since in this case, as line 50 suggests,
165 double_rq_lock actually acquires a nested lock of two spinlocks.
167 View the top contending locks:
169 # grep : /proc/lock_stat | head
170 clockevents_lock: 2926159 2947636 0.15 46882.81 1784540466.34 605.41 3381345 3879161 0.00 2260.97 53178395.68 13.71
171 tick_broadcast_lock: 346460 346717 0.18 2257.43 39364622.71 113.54 3642919 4242696 0.00 2263.79 49173646.60 11.59
172 &mapping->i_mmap_mutex: 203896 203899 3.36 645530.05 31767507988.39 155800.21 3361776 8893984 0.17 2254.15 14110121.02 1.59
173 &rq->lock: 135014 136909 0.18 606.09 842160.68 6.15 1540728 10436146 0.00 728.72 17606683.41 1.69
174 &(&zone->lru_lock)->rlock: 93000 94934 0.16 59.18 188253.78 1.98 1199912 3809894 0.15 391.40 3559518.81 0.93
175 tasklist_lock-W: 40667 41130 0.23 1189.42 428980.51 10.43 270278 510106 0.16 653.51 3939674.91 7.72
176 tasklist_lock-R: 21298 21305 0.20 1310.05 215511.12 10.12 186204 241258 0.14 1162.33 1179779.23 4.89
177 rcu_node_1: 47656 49022 0.16 635.41 193616.41 3.95 844888 1865423 0.00 764.26 1656226.96 0.89
178 &(&dentry->d_lockref.lock)->rlock: 39791 40179 0.15 1302.08 88851.96 2.21 2790851 12527025 0.10 1910.75 3379714.27 0.27
179 rcu_node_0: 29203 30064 0.16 786.55 1555573.00 51.74 88963 244254 0.00 398.87 428872.51 1.76
181 Clear the statistics:
183 # echo 0 > /proc/lock_stat