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Diffstat (limited to 'Documentation/lockstat.txt')
| -rw-r--r-- | Documentation/lockstat.txt | 179 |
1 files changed, 0 insertions, 179 deletions
diff --git a/Documentation/lockstat.txt b/Documentation/lockstat.txt deleted file mode 100644 index dd2f7b26ca30..000000000000 --- a/Documentation/lockstat.txt +++ /dev/null @@ -1,179 +0,0 @@ - -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_STAT. - - - 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 |