Now available: The Design and Implementation of the FreeBSD Operating System (Second Edition)
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FreeBSD/Linux Kernel Cross Reference
sys/Documentation/lockstat.txt
Version:
- FREEBSD - FREEBSD-13-STABLE - FREEBSD-13-0 - FREEBSD-12-STABLE - FREEBSD-12-0 - FREEBSD-11-STABLE - FREEBSD-11-0 - FREEBSD-10-STABLE - FREEBSD-10-0 - FREEBSD-9-STABLE - FREEBSD-9-0 - FREEBSD-8-STABLE - FREEBSD-8-0 - FREEBSD-7-STABLE - FREEBSD-7-0 - FREEBSD-6-STABLE - FREEBSD-6-0 - FREEBSD-5-STABLE - FREEBSD-5-0 - FREEBSD-4-STABLE - FREEBSD-3-STABLE - FREEBSD22 - l41 - OPENBSD - linux-2.6 - MK84 - PLAN9 - xnu-8792
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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/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 acq-bounces - number of lock acquisitions that involved x-cpu data 51 acquisitions - number of times we took the lock 52 hold time min - shortest (non-0) time we ever held the lock 53 max - longest time we ever held the lock 54 total - total time this lock was held 55 56 From these number various other statistics can be derived, such as: 57 58 hold time average = hold time total / acquisitions 59 60 These numbers are gathered per lock class, per read/write state (when 61 applicable). 62 63 It also tracks 4 contention points per class. A contention point is a call site 64 that had to wait on lock acquisition. 65 66 - CONFIGURATION 67 68 Lock statistics are enabled via CONFIG_LOCK_STATS. 69 70 - USAGE 71 72 Enable collection of statistics: 73 74 # echo 1 >/proc/sys/kernel/lock_stat 75 76 Disable collection of statistics: 77 78 # echo 0 >/proc/sys/kernel/lock_stat 79 80 Look at the current lock statistics: 81 82 ( line numbers not part of actual output, done for clarity in the explanation 83 below ) 84 85 # less /proc/lock_stat 86 87 01 lock_stat version 0.3 88 02 ----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- 89 03 class name con-bounces contentions waittime-min waittime-max waittime-total acq-bounces acquisitions holdtime-min holdtime-max holdtime-total 90 04 ----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- 91 05 92 06 &mm->mmap_sem-W: 233 538 18446744073708 22924.27 607243.51 1342 45806 1.71 8595.89 1180582.34 93 07 &mm->mmap_sem-R: 205 587 18446744073708 28403.36 731975.00 1940 412426 0.58 187825.45 6307502.88 94 08 --------------- 95 09 &mm->mmap_sem 487 [<ffffffff8053491f>] do_page_fault+0x466/0x928 96 10 &mm->mmap_sem 179 [<ffffffff802a6200>] sys_mprotect+0xcd/0x21d 97 11 &mm->mmap_sem 279 [<ffffffff80210a57>] sys_mmap+0x75/0xce 98 12 &mm->mmap_sem 76 [<ffffffff802a490b>] sys_munmap+0x32/0x59 99 13 --------------- 100 14 &mm->mmap_sem 270 [<ffffffff80210a57>] sys_mmap+0x75/0xce 101 15 &mm->mmap_sem 431 [<ffffffff8053491f>] do_page_fault+0x466/0x928 102 16 &mm->mmap_sem 138 [<ffffffff802a490b>] sys_munmap+0x32/0x59 103 17 &mm->mmap_sem 145 [<ffffffff802a6200>] sys_mprotect+0xcd/0x21d 104 18 105 19 ............................................................................................................................................................................................... 106 20 107 21 dcache_lock: 621 623 0.52 118.26 1053.02 6745 91930 0.29 316.29 118423.41 108 22 ----------- 109 23 dcache_lock 179 [<ffffffff80378274>] _atomic_dec_and_lock+0x34/0x54 110 24 dcache_lock 113 [<ffffffff802cc17b>] d_alloc+0x19a/0x1eb 111 25 dcache_lock 99 [<ffffffff802ca0dc>] d_rehash+0x1b/0x44 112 26 dcache_lock 104 [<ffffffff802cbca0>] d_instantiate+0x36/0x8a 113 27 ----------- 114 28 dcache_lock 192 [<ffffffff80378274>] _atomic_dec_and_lock+0x34/0x54 115 29 dcache_lock 98 [<ffffffff802ca0dc>] d_rehash+0x1b/0x44 116 30 dcache_lock 72 [<ffffffff802cc17b>] d_alloc+0x19a/0x1eb 117 31 dcache_lock 112 [<ffffffff802cbca0>] d_instantiate+0x36/0x8a 118 119 This excerpt shows the first two lock class statistics. Line 01 shows the 120 output version - each time the format changes this will be updated. Line 02-04 121 show the header with column descriptions. Lines 05-18 and 20-31 show the actual 122 statistics. These statistics come in two parts; the actual stats separated by a 123 short separator (line 08, 13) from the contention points. 124 125 The first lock (05-18) is a read/write lock, and shows two lines above the 126 short separator. The contention points don't match the column descriptors, 127 they have two: contentions and [<IP>] symbol. The second set of contention 128 points are the points we're contending with. 129 130 The integer part of the time values is in us. 131 132 Dealing with nested locks, subclasses may appear: 133 134 32............................................................................................................................................................................................... 135 33 136 34 &rq->lock: 13128 13128 0.43 190.53 103881.26 97454 3453404 0.00 401.11 13224683.11 137 35 --------- 138 36 &rq->lock 645 [<ffffffff8103bfc4>] task_rq_lock+0x43/0x75 139 37 &rq->lock 297 [<ffffffff8104ba65>] try_to_wake_up+0x127/0x25a 140 38 &rq->lock 360 [<ffffffff8103c4c5>] select_task_rq_fair+0x1f0/0x74a 141 39 &rq->lock 428 [<ffffffff81045f98>] scheduler_tick+0x46/0x1fb 142 40 --------- 143 41 &rq->lock 77 [<ffffffff8103bfc4>] task_rq_lock+0x43/0x75 144 42 &rq->lock 174 [<ffffffff8104ba65>] try_to_wake_up+0x127/0x25a 145 43 &rq->lock 4715 [<ffffffff8103ed4b>] double_rq_lock+0x42/0x54 146 44 &rq->lock 893 [<ffffffff81340524>] schedule+0x157/0x7b8 147 45 148 46............................................................................................................................................................................................... 149 47 150 48 &rq->lock/1: 11526 11488 0.33 388.73 136294.31 21461 38404 0.00 37.93 109388.53 151 49 ----------- 152 50 &rq->lock/1 11526 [<ffffffff8103ed58>] double_rq_lock+0x4f/0x54 153 51 ----------- 154 52 &rq->lock/1 5645 [<ffffffff8103ed4b>] double_rq_lock+0x42/0x54 155 53 &rq->lock/1 1224 [<ffffffff81340524>] schedule+0x157/0x7b8 156 54 &rq->lock/1 4336 [<ffffffff8103ed58>] double_rq_lock+0x4f/0x54 157 55 &rq->lock/1 181 [<ffffffff8104ba65>] try_to_wake_up+0x127/0x25a 158 159 Line 48 shows statistics for the second subclass (/1) of &rq->lock class 160 (subclass starts from 0), since in this case, as line 50 suggests, 161 double_rq_lock actually acquires a nested lock of two spinlocks. 162 163 View the top contending locks: 164 165 # grep : /proc/lock_stat | head 166 &inode->i_data.tree_lock-W: 15 21657 0.18 1093295.30 11547131054.85 58 10415 0.16 87.51 6387.60 167 &inode->i_data.tree_lock-R: 0 0 0.00 0.00 0.00 23302 231198 0.25 8.45 98023.38 168 dcache_lock: 1037 1161 0.38 45.32 774.51 6611 243371 0.15 306.48 77387.24 169 &inode->i_mutex: 161 286 18446744073709 62882.54 1244614.55 3653 20598 18446744073709 62318.60 1693822.74 170 &zone->lru_lock: 94 94 0.53 7.33 92.10 4366 32690 0.29 59.81 16350.06 171 &inode->i_data.i_mmap_mutex: 79 79 0.40 3.77 53.03 11779 87755 0.28 116.93 29898.44 172 &q->__queue_lock: 48 50 0.52 31.62 86.31 774 13131 0.17 113.08 12277.52 173 &rq->rq_lock_key: 43 47 0.74 68.50 170.63 3706 33929 0.22 107.99 17460.62 174 &rq->rq_lock_key#2: 39 46 0.75 6.68 49.03 2979 32292 0.17 125.17 17137.63 175 tasklist_lock-W: 15 15 1.45 10.87 32.70 1201 7390 0.58 62.55 13648.47 176 177 Clear the statistics: 178 179 # echo 0 > /proc/lock_stat
Cache object: df1730ecb9936d3e8debe7e6b96ce449
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