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Peter Zijlstraa560aa42007-10-07 00:24:33 -07001
2LOCK STATISTICS
3
4- WHAT
5
6As the name suggests, it provides statistics on locks.
7
8- WHY
9
10Because things like lock contention can severely impact performance.
11
12- HOW
13
14Lockdep already has hooks in the lock functions and maps lock instances to
Davidlohr Bueso214e0ae2014-07-30 13:41:55 -070015lock classes. We build on that (see Documentation/lokcing/lockdep-design.txt).
Juri Lellif62508f2011-05-19 12:53:53 +020016The graph below shows the relation between the lock functions and the various
17hooks therein.
Peter Zijlstraa560aa42007-10-07 00:24:33 -070018
19 __acquire
20 |
21 lock _____
22 | \
23 | __contended
24 | |
25 | <wait>
26 | _______/
27 |/
28 |
29 __acquired
30 |
31 .
32 <hold>
33 .
34 |
35 __release
36 |
37 unlock
38
39lock, unlock - the regular lock functions
40__* - the hooks
41<> - states
42
43With these hooks we provide the following statistics:
44
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
Davidlohr Bueso1232e382013-10-08 20:37:16 -070049 total - total time we spend waiting on this lock
50 avg - average time spent waiting on this lock
Peter Zijlstraa560aa42007-10-07 00:24:33 -070051 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
Davidlohr Bueso1232e382013-10-08 20:37:16 -070054 max - longest time we ever held the lock
55 total - total time this lock was held
56 avg - average time this lock was held
Peter Zijlstraa560aa42007-10-07 00:24:33 -070057
58These numbers are gathered per lock class, per read/write state (when
59applicable).
60
61It also tracks 4 contention points per class. A contention point is a call site
62that had to wait on lock acquisition.
63
Frank Rowandf5754bf2009-11-19 13:54:05 -080064 - CONFIGURATION
65
Yuanhan Liu0be5c8f2013-01-24 17:22:44 +080066Lock statistics are enabled via CONFIG_LOCK_STAT.
Frank Rowandf5754bf2009-11-19 13:54:05 -080067
Peter Zijlstraa560aa42007-10-07 00:24:33 -070068 - USAGE
69
Frank Rowandf5754bf2009-11-19 13:54:05 -080070Enable collection of statistics:
71
72# echo 1 >/proc/sys/kernel/lock_stat
73
74Disable collection of statistics:
75
76# echo 0 >/proc/sys/kernel/lock_stat
77
Peter Zijlstraa560aa42007-10-07 00:24:33 -070078Look at the current lock statistics:
79
80( line numbers not part of actual output, done for clarity in the explanation
81 below )
82
83# less /proc/lock_stat
84
Davidlohr Bueso1232e382013-10-08 20:37:16 -07008501 lock_stat version 0.4
8602-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
8703 class name con-bounces contentions waittime-min waittime-max waittime-total waittime-avg acq-bounces acquisitions holdtime-min holdtime-max holdtime-total holdtime-avg
8804-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
Peter Zijlstraa560aa42007-10-07 00:24:33 -07008905
Davidlohr Bueso1232e382013-10-08 20:37:16 -07009006 &mm->mmap_sem-W: 46 84 0.26 939.10 16371.53 194.90 47291 2922365 0.16 2220301.69 17464026916.32 5975.99
9107 &mm->mmap_sem-R: 37 100 1.31 299502.61 325629.52 3256.30 212344 34316685 0.10 7744.91 95016910.20 2.77
9208 ---------------
9309 &mm->mmap_sem 1 [<ffffffff811502a7>] khugepaged_scan_mm_slot+0x57/0x280
9419 &mm->mmap_sem 96 [<ffffffff815351c4>] __do_page_fault+0x1d4/0x510
9511 &mm->mmap_sem 34 [<ffffffff81113d77>] vm_mmap_pgoff+0x87/0xd0
9612 &mm->mmap_sem 17 [<ffffffff81127e71>] vm_munmap+0x41/0x80
9713 ---------------
9814 &mm->mmap_sem 1 [<ffffffff81046fda>] dup_mmap+0x2a/0x3f0
9915 &mm->mmap_sem 60 [<ffffffff81129e29>] SyS_mprotect+0xe9/0x250
10016 &mm->mmap_sem 41 [<ffffffff815351c4>] __do_page_fault+0x1d4/0x510
10117 &mm->mmap_sem 68 [<ffffffff81113d77>] vm_mmap_pgoff+0x87/0xd0
Peter Zijlstrac7e78cf2008-10-16 23:17:09 +020010218
Davidlohr Bueso1232e382013-10-08 20:37:16 -070010319.............................................................................................................................................................................................................................
Peter Zijlstrac7e78cf2008-10-16 23:17:09 +020010420
Davidlohr Bueso1232e382013-10-08 20:37:16 -070010521 unix_table_lock: 110 112 0.21 49.24 163.91 1.46 21094 66312 0.12 624.42 31589.81 0.48
10622 ---------------
10723 unix_table_lock 45 [<ffffffff8150ad8e>] unix_create1+0x16e/0x1b0
10824 unix_table_lock 47 [<ffffffff8150b111>] unix_release_sock+0x31/0x250
10925 unix_table_lock 15 [<ffffffff8150ca37>] unix_find_other+0x117/0x230
11026 unix_table_lock 5 [<ffffffff8150a09f>] unix_autobind+0x11f/0x1b0
11127 ---------------
11228 unix_table_lock 39 [<ffffffff8150b111>] unix_release_sock+0x31/0x250
11329 unix_table_lock 49 [<ffffffff8150ad8e>] unix_create1+0x16e/0x1b0
11430 unix_table_lock 20 [<ffffffff8150ca37>] unix_find_other+0x117/0x230
11531 unix_table_lock 4 [<ffffffff8150a09f>] unix_autobind+0x11f/0x1b0
116
Peter Zijlstraa560aa42007-10-07 00:24:33 -0700117
118This excerpt shows the first two lock class statistics. Line 01 shows the
119output version - each time the format changes this will be updated. Line 02-04
Peter Zijlstrac7e78cf2008-10-16 23:17:09 +0200120show the header with column descriptions. Lines 05-18 and 20-31 show the actual
Peter Zijlstraa560aa42007-10-07 00:24:33 -0700121statistics. These statistics come in two parts; the actual stats separated by a
Peter Zijlstrac7e78cf2008-10-16 23:17:09 +0200122short separator (line 08, 13) from the contention points.
Peter Zijlstraa560aa42007-10-07 00:24:33 -0700123
Peter Zijlstrac7e78cf2008-10-16 23:17:09 +0200124The first lock (05-18) is a read/write lock, and shows two lines above the
Peter Zijlstraa560aa42007-10-07 00:24:33 -0700125short separator. The contention points don't match the column descriptors,
Peter Zijlstrac7e78cf2008-10-16 23:17:09 +0200126they have two: contentions and [<IP>] symbol. The second set of contention
127points are the points we're contending with.
Peter Zijlstraa560aa42007-10-07 00:24:33 -0700128
Peter Zijlstracdad7222008-09-03 16:00:57 +0200129The integer part of the time values is in us.
Peter Zijlstraa560aa42007-10-07 00:24:33 -0700130
Juri Lellif62508f2011-05-19 12:53:53 +0200131Dealing with nested locks, subclasses may appear:
132
Davidlohr Bueso1232e382013-10-08 20:37:16 -070013332...........................................................................................................................................................................................................................
Juri Lellif62508f2011-05-19 12:53:53 +020013433
Davidlohr Bueso1232e382013-10-08 20:37:16 -070013534 &rq->lock: 13128 13128 0.43 190.53 103881.26 7.91 97454 3453404 0.00 401.11 13224683.11 3.82
Juri Lellif62508f2011-05-19 12:53:53 +020013635 ---------
Davidlohr Bueso1232e382013-10-08 20:37:16 -070013736 &rq->lock 645 [<ffffffff8103bfc4>] task_rq_lock+0x43/0x75
13837 &rq->lock 297 [<ffffffff8104ba65>] try_to_wake_up+0x127/0x25a
13938 &rq->lock 360 [<ffffffff8103c4c5>] select_task_rq_fair+0x1f0/0x74a
14039 &rq->lock 428 [<ffffffff81045f98>] scheduler_tick+0x46/0x1fb
Juri Lellif62508f2011-05-19 12:53:53 +020014140 ---------
Davidlohr Bueso1232e382013-10-08 20:37:16 -070014241 &rq->lock 77 [<ffffffff8103bfc4>] task_rq_lock+0x43/0x75
14342 &rq->lock 174 [<ffffffff8104ba65>] try_to_wake_up+0x127/0x25a
14443 &rq->lock 4715 [<ffffffff8103ed4b>] double_rq_lock+0x42/0x54
14544 &rq->lock 893 [<ffffffff81340524>] schedule+0x157/0x7b8
Juri Lellif62508f2011-05-19 12:53:53 +020014645
Davidlohr Bueso1232e382013-10-08 20:37:16 -070014746...........................................................................................................................................................................................................................
Juri Lellif62508f2011-05-19 12:53:53 +020014847
Davidlohr Bueso1232e382013-10-08 20:37:16 -070014948 &rq->lock/1: 1526 11488 0.33 388.73 136294.31 11.86 21461 38404 0.00 37.93 109388.53 2.84
Juri Lellif62508f2011-05-19 12:53:53 +020015049 -----------
Davidlohr Bueso1232e382013-10-08 20:37:16 -070015150 &rq->lock/1 11526 [<ffffffff8103ed58>] double_rq_lock+0x4f/0x54
Juri Lellif62508f2011-05-19 12:53:53 +020015251 -----------
Davidlohr Bueso1232e382013-10-08 20:37:16 -070015352 &rq->lock/1 5645 [<ffffffff8103ed4b>] double_rq_lock+0x42/0x54
15453 &rq->lock/1 1224 [<ffffffff81340524>] schedule+0x157/0x7b8
15554 &rq->lock/1 4336 [<ffffffff8103ed58>] double_rq_lock+0x4f/0x54
15655 &rq->lock/1 181 [<ffffffff8104ba65>] try_to_wake_up+0x127/0x25a
Juri Lellif62508f2011-05-19 12:53:53 +0200157
158Line 48 shows statistics for the second subclass (/1) of &rq->lock class
159(subclass starts from 0), since in this case, as line 50 suggests,
160double_rq_lock actually acquires a nested lock of two spinlocks.
161
Peter Zijlstraa560aa42007-10-07 00:24:33 -0700162View the top contending locks:
163
164# grep : /proc/lock_stat | head
Davidlohr Bueso1232e382013-10-08 20:37:16 -0700165 clockevents_lock: 2926159 2947636 0.15 46882.81 1784540466.34 605.41 3381345 3879161 0.00 2260.97 53178395.68 13.71
166 tick_broadcast_lock: 346460 346717 0.18 2257.43 39364622.71 113.54 3642919 4242696 0.00 2263.79 49173646.60 11.59
167 &mapping->i_mmap_mutex: 203896 203899 3.36 645530.05 31767507988.39 155800.21 3361776 8893984 0.17 2254.15 14110121.02 1.59
168 &rq->lock: 135014 136909 0.18 606.09 842160.68 6.15 1540728 10436146 0.00 728.72 17606683.41 1.69
169 &(&zone->lru_lock)->rlock: 93000 94934 0.16 59.18 188253.78 1.98 1199912 3809894 0.15 391.40 3559518.81 0.93
170 tasklist_lock-W: 40667 41130 0.23 1189.42 428980.51 10.43 270278 510106 0.16 653.51 3939674.91 7.72
171 tasklist_lock-R: 21298 21305 0.20 1310.05 215511.12 10.12 186204 241258 0.14 1162.33 1179779.23 4.89
172 rcu_node_1: 47656 49022 0.16 635.41 193616.41 3.95 844888 1865423 0.00 764.26 1656226.96 0.89
173 &(&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
174 rcu_node_0: 29203 30064 0.16 786.55 1555573.00 51.74 88963 244254 0.00 398.87 428872.51 1.76
Peter Zijlstraa560aa42007-10-07 00:24:33 -0700175
176Clear the statistics:
177
178# echo 0 > /proc/lock_stat