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