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- LOCK STATISTICS
- - WHAT
- As the name suggests, it provides statistics on locks.
- - WHY
- Because things like lock contention can severely impact performance.
- - HOW
- Lockdep already has hooks in the lock functions and maps lock instances to
- lock classes. We build on that (see Documentation/lockdep-design.txt).
- The graph below shows the relation between the lock functions and the various
- hooks therein.
- __acquire
- |
- lock _____
- | \
- | __contended
- | |
- | <wait>
- | _______/
- |/
- |
- __acquired
- |
- .
- <hold>
- .
- |
- __release
- |
- unlock
- lock, unlock - the regular lock functions
- __* - the hooks
- <> - states
- With these hooks we provide the following statistics:
- con-bounces - number of lock contention that involved x-cpu data
- contentions - number of lock acquisitions that had to wait
- wait time min - shortest (non-0) time we ever had to wait for a lock
- max - longest time we ever had to wait for a lock
- total - total time we spend waiting on this lock
- acq-bounces - number of lock acquisitions that involved x-cpu data
- acquisitions - number of times we took the lock
- hold time min - shortest (non-0) time we ever held the lock
- max - longest time we ever held the lock
- total - total time this lock was held
- From these number various other statistics can be derived, such as:
- hold time average = hold time total / acquisitions
- These numbers are gathered per lock class, per read/write state (when
- applicable).
- It also tracks 4 contention points per class. A contention point is a call site
- that had to wait on lock acquisition.
- - CONFIGURATION
- Lock statistics are enabled via CONFIG_LOCK_STATS.
- - USAGE
- Enable collection of statistics:
- # echo 1 >/proc/sys/kernel/lock_stat
- Disable collection of statistics:
- # echo 0 >/proc/sys/kernel/lock_stat
- Look at the current lock statistics:
- ( line numbers not part of actual output, done for clarity in the explanation
- below )
- # less /proc/lock_stat
- 01 lock_stat version 0.3
- 02 -----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
- 03 class name con-bounces contentions waittime-min waittime-max waittime-total acq-bounces acquisitions holdtime-min holdtime-max holdtime-total
- 04 -----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
- 05
- 06 &mm->mmap_sem-W: 233 538 18446744073708 22924.27 607243.51 1342 45806 1.71 8595.89 1180582.34
- 07 &mm->mmap_sem-R: 205 587 18446744073708 28403.36 731975.00 1940 412426 0.58 187825.45 6307502.88
- 08 ---------------
- 09 &mm->mmap_sem 487 [<ffffffff8053491f>] do_page_fault+0x466/0x928
- 10 &mm->mmap_sem 179 [<ffffffff802a6200>] sys_mprotect+0xcd/0x21d
- 11 &mm->mmap_sem 279 [<ffffffff80210a57>] sys_mmap+0x75/0xce
- 12 &mm->mmap_sem 76 [<ffffffff802a490b>] sys_munmap+0x32/0x59
- 13 ---------------
- 14 &mm->mmap_sem 270 [<ffffffff80210a57>] sys_mmap+0x75/0xce
- 15 &mm->mmap_sem 431 [<ffffffff8053491f>] do_page_fault+0x466/0x928
- 16 &mm->mmap_sem 138 [<ffffffff802a490b>] sys_munmap+0x32/0x59
- 17 &mm->mmap_sem 145 [<ffffffff802a6200>] sys_mprotect+0xcd/0x21d
- 18
- 19 ...............................................................................................................................................................................................
- 20
- 21 dcache_lock: 621 623 0.52 118.26 1053.02 6745 91930 0.29 316.29 118423.41
- 22 -----------
- 23 dcache_lock 179 [<ffffffff80378274>] _atomic_dec_and_lock+0x34/0x54
- 24 dcache_lock 113 [<ffffffff802cc17b>] d_alloc+0x19a/0x1eb
- 25 dcache_lock 99 [<ffffffff802ca0dc>] d_rehash+0x1b/0x44
- 26 dcache_lock 104 [<ffffffff802cbca0>] d_instantiate+0x36/0x8a
- 27 -----------
- 28 dcache_lock 192 [<ffffffff80378274>] _atomic_dec_and_lock+0x34/0x54
- 29 dcache_lock 98 [<ffffffff802ca0dc>] d_rehash+0x1b/0x44
- 30 dcache_lock 72 [<ffffffff802cc17b>] d_alloc+0x19a/0x1eb
- 31 dcache_lock 112 [<ffffffff802cbca0>] d_instantiate+0x36/0x8a
- This excerpt shows the first two lock class statistics. Line 01 shows the
- output version - each time the format changes this will be updated. Line 02-04
- show the header with column descriptions. Lines 05-18 and 20-31 show the actual
- statistics. These statistics come in two parts; the actual stats separated by a
- short separator (line 08, 13) from the contention points.
- The first lock (05-18) is a read/write lock, and shows two lines above the
- short separator. The contention points don't match the column descriptors,
- they have two: contentions and [<IP>] symbol. The second set of contention
- points are the points we're contending with.
- The integer part of the time values is in us.
- Dealing with nested locks, subclasses may appear:
- 32...............................................................................................................................................................................................
- 33
- 34 &rq->lock: 13128 13128 0.43 190.53 103881.26 97454 3453404 0.00 401.11 13224683.11
- 35 ---------
- 36 &rq->lock 645 [<ffffffff8103bfc4>] task_rq_lock+0x43/0x75
- 37 &rq->lock 297 [<ffffffff8104ba65>] try_to_wake_up+0x127/0x25a
- 38 &rq->lock 360 [<ffffffff8103c4c5>] select_task_rq_fair+0x1f0/0x74a
- 39 &rq->lock 428 [<ffffffff81045f98>] scheduler_tick+0x46/0x1fb
- 40 ---------
- 41 &rq->lock 77 [<ffffffff8103bfc4>] task_rq_lock+0x43/0x75
- 42 &rq->lock 174 [<ffffffff8104ba65>] try_to_wake_up+0x127/0x25a
- 43 &rq->lock 4715 [<ffffffff8103ed4b>] double_rq_lock+0x42/0x54
- 44 &rq->lock 893 [<ffffffff81340524>] schedule+0x157/0x7b8
- 45
- 46...............................................................................................................................................................................................
- 47
- 48 &rq->lock/1: 11526 11488 0.33 388.73 136294.31 21461 38404 0.00 37.93 109388.53
- 49 -----------
- 50 &rq->lock/1 11526 [<ffffffff8103ed58>] double_rq_lock+0x4f/0x54
- 51 -----------
- 52 &rq->lock/1 5645 [<ffffffff8103ed4b>] double_rq_lock+0x42/0x54
- 53 &rq->lock/1 1224 [<ffffffff81340524>] schedule+0x157/0x7b8
- 54 &rq->lock/1 4336 [<ffffffff8103ed58>] double_rq_lock+0x4f/0x54
- 55 &rq->lock/1 181 [<ffffffff8104ba65>] try_to_wake_up+0x127/0x25a
- Line 48 shows statistics for the second subclass (/1) of &rq->lock class
- (subclass starts from 0), since in this case, as line 50 suggests,
- double_rq_lock actually acquires a nested lock of two spinlocks.
- View the top contending locks:
- # grep : /proc/lock_stat | head
- &inode->i_data.tree_lock-W: 15 21657 0.18 1093295.30 11547131054.85 58 10415 0.16 87.51 6387.60
- &inode->i_data.tree_lock-R: 0 0 0.00 0.00 0.00 23302 231198 0.25 8.45 98023.38
- dcache_lock: 1037 1161 0.38 45.32 774.51 6611 243371 0.15 306.48 77387.24
- &inode->i_mutex: 161 286 18446744073709 62882.54 1244614.55 3653 20598 18446744073709 62318.60 1693822.74
- &zone->lru_lock: 94 94 0.53 7.33 92.10 4366 32690 0.29 59.81 16350.06
- &inode->i_data.i_mmap_mutex: 79 79 0.40 3.77 53.03 11779 87755 0.28 116.93 29898.44
- &q->__queue_lock: 48 50 0.52 31.62 86.31 774 13131 0.17 113.08 12277.52
- &rq->rq_lock_key: 43 47 0.74 68.50 170.63 3706 33929 0.22 107.99 17460.62
- &rq->rq_lock_key#2: 39 46 0.75 6.68 49.03 2979 32292 0.17 125.17 17137.63
- tasklist_lock-W: 15 15 1.45 10.87 32.70 1201 7390 0.58 62.55 13648.47
- Clear the statistics:
- # echo 0 > /proc/lock_stat
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