Based on kernel version 2.6.25. Page generated on 2008-04-18 21:22 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. The graph below shows the relation between 16 the lock functions and the various hooks therein. 17 18 __acquire 19 | 20 lock _____ 21 | \ 22 | __contended 23 | | 24 | <wait> 25 | _______/ 26 |/ 27 | 28 __acquired 29 | 30 . 31 <hold> 32 . 33 | 34 __release 35 | 36 unlock 37 38 lock, unlock - the regular lock functions 39 __* - the hooks 40 <> - states 41 42 With these hooks we provide the following statistics: 43 44 con-bounces - number of lock contention that involved x-cpu data 45 contentions - number of lock acquisitions that had to wait 46 wait time min - shortest (non-0) time we ever had to wait for a lock 47 max - longest time we ever had to wait for a lock 48 total - total time we spend waiting on this lock 49 acq-bounces - number of lock acquisitions that involved x-cpu data 50 acquisitions - number of times we took the lock 51 hold time min - shortest (non-0) time we ever held the lock 52 max - longest time we ever held the lock 53 total - total time this lock was held 54 55 From these number various other statistics can be derived, such as: 56 57 hold time average = hold time total / acquisitions 58 59 These numbers are gathered per lock class, per read/write state (when 60 applicable). 61 62 It also tracks 4 contention points per class. A contention point is a call site 63 that had to wait on lock acquisition. 64 65 - USAGE 66 67 Look at the current lock statistics: 68 69 ( line numbers not part of actual output, done for clarity in the explanation 70 below ) 71 72 # less /proc/lock_stat 73 74 01 lock_stat version 0.2 75 02 ----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- 76 03 class name con-bounces contentions waittime-min waittime-max waittime-total acq-bounces acquisitions holdtime-min holdtime-max holdtime-total 77 04 ----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- 78 05 79 06 &inode->i_data.tree_lock-W: 15 21657 0.18 1093295.30 11547131054.85 58 10415 0.16 87.51 6387.60 80 07 &inode->i_data.tree_lock-R: 0 0 0.00 0.00 0.00 23302 231198 0.25 8.45 98023.38 81 08 -------------------------- 82 09 &inode->i_data.tree_lock 0 [<ffffffff8027c08f>] add_to_page_cache+0x5f/0x190 83 10 84 11 ............................................................................................................................................................................................... 85 12 86 13 dcache_lock: 1037 1161 0.38 45.32 774.51 6611 243371 0.15 306.48 77387.24 87 14 ----------- 88 15 dcache_lock 180 [<ffffffff802c0d7e>] sys_getcwd+0x11e/0x230 89 16 dcache_lock 165 [<ffffffff802c002a>] d_alloc+0x15a/0x210 90 17 dcache_lock 33 [<ffffffff8035818d>] _atomic_dec_and_lock+0x4d/0x70 91 18 dcache_lock 1 [<ffffffff802beef8>] shrink_dcache_parent+0x18/0x130 92 93 This excerpt shows the first two lock class statistics. Line 01 shows the 94 output version - each time the format changes this will be updated. Line 02-04 95 show the header with column descriptions. Lines 05-10 and 13-18 show the actual 96 statistics. These statistics come in two parts; the actual stats separated by a 97 short separator (line 08, 14) from the contention points. 98 99 The first lock (05-10) is a read/write lock, and shows two lines above the 100 short separator. The contention points don't match the column descriptors, 101 they have two: contentions and [<IP>] symbol. 102 103 104 View the top contending locks: 105 106 # grep : /proc/lock_stat | head 107 &inode->i_data.tree_lock-W: 15 21657 0.18 1093295.30 11547131054.85 58 10415 0.16 87.51 6387.60 108 &inode->i_data.tree_lock-R: 0 0 0.00 0.00 0.00 23302 231198 0.25 8.45 98023.38 109 dcache_lock: 1037 1161 0.38 45.32 774.51 6611 243371 0.15 306.48 77387.24 110 &inode->i_mutex: 161 286 18446744073709 62882.54 1244614.55 3653 20598 18446744073709 62318.60 1693822.74 111 &zone->lru_lock: 94 94 0.53 7.33 92.10 4366 32690 0.29 59.81 16350.06 112 &inode->i_data.i_mmap_lock: 79 79 0.40 3.77 53.03 11779 87755 0.28 116.93 29898.44 113 &q->__queue_lock: 48 50 0.52 31.62 86.31 774 13131 0.17 113.08 12277.52 114 &rq->rq_lock_key: 43 47 0.74 68.50 170.63 3706 33929 0.22 107.99 17460.62 115 &rq->rq_lock_key#2: 39 46 0.75 6.68 49.03 2979 32292 0.17 125.17 17137.63 116 tasklist_lock-W: 15 15 1.45 10.87 32.70 1201 7390 0.58 62.55 13648.47 117 118 Clear the statistics: 119 120 # echo 0 > /proc/lock_stat
