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Commit | Line | Data |
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387b1468 MCC |
1 | =============== |
2 | Lock Statistics | |
3 | =============== | |
4 | ||
5 | What | |
6 | ==== | |
7 | ||
8 | As the name suggests, it provides statistics on locks. | |
9 | ||
10 | ||
11 | Why | |
12 | === | |
13 | ||
14 | Because things like lock contention can severely impact performance. | |
15 | ||
16 | How | |
17 | === | |
18 | ||
19 | Lockdep already has hooks in the lock functions and maps lock instances to | |
20 | lock classes. We build on that (see Documentation/locking/lockdep-design.rst). | |
21 | The graph below shows the relation between the lock functions and the various | |
22 | hooks therein:: | |
23 | ||
24 | __acquire | |
25 | | | |
26 | lock _____ | |
27 | | \ | |
28 | | __contended | |
29 | | | | |
30 | | <wait> | |
31 | | _______/ | |
32 | |/ | |
33 | | | |
34 | __acquired | |
35 | | | |
36 | . | |
37 | <hold> | |
38 | . | |
39 | | | |
40 | __release | |
41 | | | |
42 | unlock | |
43 | ||
44 | lock, unlock - the regular lock functions | |
45 | __* - the hooks | |
46 | <> - states | |
47 | ||
48 | With these hooks we provide the following statistics: | |
49 | ||
50 | con-bounces | |
51 | - number of lock contention that involved x-cpu data | |
52 | contentions | |
53 | - number of lock acquisitions that had to wait | |
54 | wait time | |
55 | min | |
56 | - shortest (non-0) time we ever had to wait for a lock | |
57 | max | |
58 | - longest time we ever had to wait for a lock | |
59 | total | |
60 | - total time we spend waiting on this lock | |
61 | avg | |
62 | - average time spent waiting on this lock | |
63 | acq-bounces | |
64 | - number of lock acquisitions that involved x-cpu data | |
65 | acquisitions | |
66 | - number of times we took the lock | |
67 | hold time | |
68 | min | |
69 | - shortest (non-0) time we ever held the lock | |
70 | max | |
71 | - longest time we ever held the lock | |
72 | total | |
73 | - total time this lock was held | |
74 | avg | |
75 | - average time this lock was held | |
76 | ||
77 | These numbers are gathered per lock class, per read/write state (when | |
78 | applicable). | |
79 | ||
80 | It also tracks 4 contention points per class. A contention point is a call site | |
81 | that had to wait on lock acquisition. | |
82 | ||
83 | Configuration | |
84 | ------------- | |
85 | ||
86 | Lock statistics are enabled via CONFIG_LOCK_STAT. | |
87 | ||
88 | Usage | |
89 | ----- | |
90 | ||
91 | Enable collection of statistics:: | |
92 | ||
93 | # echo 1 >/proc/sys/kernel/lock_stat | |
94 | ||
95 | Disable collection of statistics:: | |
96 | ||
97 | # echo 0 >/proc/sys/kernel/lock_stat | |
98 | ||
99 | Look at the current lock statistics:: | |
100 | ||
101 | ( line numbers not part of actual output, done for clarity in the explanation | |
102 | below ) | |
103 | ||
104 | # less /proc/lock_stat | |
105 | ||
106 | 01 lock_stat version 0.4 | |
107 | 02----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- | |
108 | 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 | |
109 | 04----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- | |
110 | 05 | |
111 | 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 | |
112 | 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 | |
113 | 08 --------------- | |
114 | 09 &mm->mmap_sem 1 [<ffffffff811502a7>] khugepaged_scan_mm_slot+0x57/0x280 | |
115 | 10 &mm->mmap_sem 96 [<ffffffff815351c4>] __do_page_fault+0x1d4/0x510 | |
116 | 11 &mm->mmap_sem 34 [<ffffffff81113d77>] vm_mmap_pgoff+0x87/0xd0 | |
117 | 12 &mm->mmap_sem 17 [<ffffffff81127e71>] vm_munmap+0x41/0x80 | |
118 | 13 --------------- | |
119 | 14 &mm->mmap_sem 1 [<ffffffff81046fda>] dup_mmap+0x2a/0x3f0 | |
120 | 15 &mm->mmap_sem 60 [<ffffffff81129e29>] SyS_mprotect+0xe9/0x250 | |
121 | 16 &mm->mmap_sem 41 [<ffffffff815351c4>] __do_page_fault+0x1d4/0x510 | |
122 | 17 &mm->mmap_sem 68 [<ffffffff81113d77>] vm_mmap_pgoff+0x87/0xd0 | |
123 | 18 | |
124 | 19............................................................................................................................................................................................................................. | |
125 | 20 | |
126 | 21 unix_table_lock: 110 112 0.21 49.24 163.91 1.46 21094 66312 0.12 624.42 31589.81 0.48 | |
127 | 22 --------------- | |
128 | 23 unix_table_lock 45 [<ffffffff8150ad8e>] unix_create1+0x16e/0x1b0 | |
129 | 24 unix_table_lock 47 [<ffffffff8150b111>] unix_release_sock+0x31/0x250 | |
130 | 25 unix_table_lock 15 [<ffffffff8150ca37>] unix_find_other+0x117/0x230 | |
131 | 26 unix_table_lock 5 [<ffffffff8150a09f>] unix_autobind+0x11f/0x1b0 | |
132 | 27 --------------- | |
133 | 28 unix_table_lock 39 [<ffffffff8150b111>] unix_release_sock+0x31/0x250 | |
134 | 29 unix_table_lock 49 [<ffffffff8150ad8e>] unix_create1+0x16e/0x1b0 | |
135 | 30 unix_table_lock 20 [<ffffffff8150ca37>] unix_find_other+0x117/0x230 | |
136 | 31 unix_table_lock 4 [<ffffffff8150a09f>] unix_autobind+0x11f/0x1b0 | |
137 | ||
138 | ||
139 | This excerpt shows the first two lock class statistics. Line 01 shows the | |
140 | output version - each time the format changes this will be updated. Line 02-04 | |
141 | show the header with column descriptions. Lines 05-18 and 20-31 show the actual | |
142 | statistics. These statistics come in two parts; the actual stats separated by a | |
143 | short separator (line 08, 13) from the contention points. | |
144 | ||
145 | Lines 09-12 show the first 4 recorded contention points (the code | |
146 | which tries to get the lock) and lines 14-17 show the first 4 recorded | |
147 | contended points (the lock holder). It is possible that the max | |
148 | con-bounces point is missing in the statistics. | |
149 | ||
150 | The first lock (05-18) is a read/write lock, and shows two lines above the | |
151 | short separator. The contention points don't match the column descriptors, | |
152 | they have two: contentions and [<IP>] symbol. The second set of contention | |
153 | points are the points we're contending with. | |
154 | ||
155 | The integer part of the time values is in us. | |
156 | ||
157 | Dealing with nested locks, subclasses may appear:: | |
158 | ||
159 | 32........................................................................................................................................................................................................................... | |
160 | 33 | |
161 | 34 &rq->lock: 13128 13128 0.43 190.53 103881.26 7.91 97454 3453404 0.00 401.11 13224683.11 3.82 | |
162 | 35 --------- | |
163 | 36 &rq->lock 645 [<ffffffff8103bfc4>] task_rq_lock+0x43/0x75 | |
164 | 37 &rq->lock 297 [<ffffffff8104ba65>] try_to_wake_up+0x127/0x25a | |
165 | 38 &rq->lock 360 [<ffffffff8103c4c5>] select_task_rq_fair+0x1f0/0x74a | |
166 | 39 &rq->lock 428 [<ffffffff81045f98>] scheduler_tick+0x46/0x1fb | |
167 | 40 --------- | |
168 | 41 &rq->lock 77 [<ffffffff8103bfc4>] task_rq_lock+0x43/0x75 | |
169 | 42 &rq->lock 174 [<ffffffff8104ba65>] try_to_wake_up+0x127/0x25a | |
170 | 43 &rq->lock 4715 [<ffffffff8103ed4b>] double_rq_lock+0x42/0x54 | |
171 | 44 &rq->lock 893 [<ffffffff81340524>] schedule+0x157/0x7b8 | |
172 | 45 | |
173 | 46........................................................................................................................................................................................................................... | |
174 | 47 | |
175 | 48 &rq->lock/1: 1526 11488 0.33 388.73 136294.31 11.86 21461 38404 0.00 37.93 109388.53 2.84 | |
176 | 49 ----------- | |
177 | 50 &rq->lock/1 11526 [<ffffffff8103ed58>] double_rq_lock+0x4f/0x54 | |
178 | 51 ----------- | |
179 | 52 &rq->lock/1 5645 [<ffffffff8103ed4b>] double_rq_lock+0x42/0x54 | |
180 | 53 &rq->lock/1 1224 [<ffffffff81340524>] schedule+0x157/0x7b8 | |
181 | 54 &rq->lock/1 4336 [<ffffffff8103ed58>] double_rq_lock+0x4f/0x54 | |
182 | 55 &rq->lock/1 181 [<ffffffff8104ba65>] try_to_wake_up+0x127/0x25a | |
183 | ||
184 | Line 48 shows statistics for the second subclass (/1) of &rq->lock class | |
185 | (subclass starts from 0), since in this case, as line 50 suggests, | |
186 | double_rq_lock actually acquires a nested lock of two spinlocks. | |
187 | ||
188 | View the top contending locks:: | |
189 | ||
190 | # grep : /proc/lock_stat | head | |
191 | clockevents_lock: 2926159 2947636 0.15 46882.81 1784540466.34 605.41 3381345 3879161 0.00 2260.97 53178395.68 13.71 | |
192 | tick_broadcast_lock: 346460 346717 0.18 2257.43 39364622.71 113.54 3642919 4242696 0.00 2263.79 49173646.60 11.59 | |
193 | &mapping->i_mmap_mutex: 203896 203899 3.36 645530.05 31767507988.39 155800.21 3361776 8893984 0.17 2254.15 14110121.02 1.59 | |
194 | &rq->lock: 135014 136909 0.18 606.09 842160.68 6.15 1540728 10436146 0.00 728.72 17606683.41 1.69 | |
195 | &(&zone->lru_lock)->rlock: 93000 94934 0.16 59.18 188253.78 1.98 1199912 3809894 0.15 391.40 3559518.81 0.93 | |
196 | tasklist_lock-W: 40667 41130 0.23 1189.42 428980.51 10.43 270278 510106 0.16 653.51 3939674.91 7.72 | |
197 | tasklist_lock-R: 21298 21305 0.20 1310.05 215511.12 10.12 186204 241258 0.14 1162.33 1179779.23 4.89 | |
198 | rcu_node_1: 47656 49022 0.16 635.41 193616.41 3.95 844888 1865423 0.00 764.26 1656226.96 0.89 | |
199 | &(&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 | |
200 | rcu_node_0: 29203 30064 0.16 786.55 1555573.00 51.74 88963 244254 0.00 398.87 428872.51 1.76 | |
201 | ||
202 | Clear the statistics:: | |
203 | ||
204 | # echo 0 > /proc/lock_stat |