Based on kernel version 4.16.1. Page generated on 2018-04-09 11:53 EST.
1 2 LOCK STATISTICS 3 4 - WHAT 5 6 As the name suggests, it provides statistics on locks. 7 8 - WHY 9 10 Because things like lock contention can severely impact performance. 11 12 - HOW 13 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 17 hooks therein. 18 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 39 lock, unlock - the regular lock functions 40 __* - the hooks 41 <> - states 42 43 With 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 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 57 58 These numbers are gathered per lock class, per read/write state (when 59 applicable). 60 61 It also tracks 4 contention points per class. A contention point is a call site 62 that had to wait on lock acquisition. 63 64 - CONFIGURATION 65 66 Lock statistics are enabled via CONFIG_LOCK_STAT. 67 68 - USAGE 69 70 Enable collection of statistics: 71 72 # echo 1 >/proc/sys/kernel/lock_stat 73 74 Disable collection of statistics: 75 76 # echo 0 >/proc/sys/kernel/lock_stat 77 78 Look 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 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----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- 89 05 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 92 08 --------------- 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 97 13 --------------- 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 102 18 103 19............................................................................................................................................................................................................................. 104 20 105 21 unix_table_lock: 110 112 0.21 49.24 163.91 1.46 21094 66312 0.12 624.42 31589.81 0.48 106 22 --------------- 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 111 27 --------------- 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 116 117 118 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. 123 124 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. 128 129 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. 133 134 The integer part of the time values is in us. 135 136 Dealing with nested locks, subclasses may appear: 137 138 32........................................................................................................................................................................................................................... 139 33 140 34 &rq->lock: 13128 13128 0.43 190.53 103881.26 7.91 97454 3453404 0.00 401.11 13224683.11 3.82 141 35 --------- 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 146 40 --------- 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 151 45 152 46........................................................................................................................................................................................................................... 153 47 154 48 &rq->lock/1: 1526 11488 0.33 388.73 136294.31 11.86 21461 38404 0.00 37.93 109388.53 2.84 155 49 ----------- 156 50 &rq->lock/1 11526 [<ffffffff8103ed58>] double_rq_lock+0x4f/0x54 157 51 ----------- 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 162 163 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. 166 167 View the top contending locks: 168 169 # 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 1.76 180 181 Clear the statistics: 182 183 # echo 0 > /proc/lock_stat