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Diffstat (limited to 'Documentation/locking/lockstat.txt')
| -rw-r--r-- | Documentation/locking/lockstat.txt | 183 |
1 files changed, 0 insertions, 183 deletions
diff --git a/Documentation/locking/lockstat.txt b/Documentation/locking/lockstat.txt deleted file mode 100644 index fdbeb0c45ef3..000000000000 --- a/Documentation/locking/lockstat.txt +++ /dev/null @@ -1,183 +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/locking/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 - avg - average time spent 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 - avg - average time this lock was held - -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 0.4 -02----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- -03 class name con-bounces contentions waittime-min waittime-max waittime-total waittime-avg acq-bounces acquisitions holdtime-min holdtime-max holdtime-total holdtime-avg -04----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- -05 -06 &mm->mmap_sem-W: 46 84 0.26 939.10 16371.53 194.90 47291 2922365 0.16 2220301.69 17464026916.32 5975.99 -07 &mm->mmap_sem-R: 37 100 1.31 299502.61 325629.52 3256.30 212344 34316685 0.10 7744.91 95016910.20 2.77 -08 --------------- -09 &mm->mmap_sem 1 [<ffffffff811502a7>] khugepaged_scan_mm_slot+0x57/0x280 -10 &mm->mmap_sem 96 [<ffffffff815351c4>] __do_page_fault+0x1d4/0x510 -11 &mm->mmap_sem 34 [<ffffffff81113d77>] vm_mmap_pgoff+0x87/0xd0 -12 &mm->mmap_sem 17 [<ffffffff81127e71>] vm_munmap+0x41/0x80 -13 --------------- -14 &mm->mmap_sem 1 [<ffffffff81046fda>] dup_mmap+0x2a/0x3f0 -15 &mm->mmap_sem 60 [<ffffffff81129e29>] SyS_mprotect+0xe9/0x250 -16 &mm->mmap_sem 41 [<ffffffff815351c4>] __do_page_fault+0x1d4/0x510 -17 &mm->mmap_sem 68 [<ffffffff81113d77>] vm_mmap_pgoff+0x87/0xd0 -18 -19............................................................................................................................................................................................................................. -20 -21 unix_table_lock: 110 112 0.21 49.24 163.91 1.46 21094 66312 0.12 624.42 31589.81 0.48 -22 --------------- -23 unix_table_lock 45 [<ffffffff8150ad8e>] unix_create1+0x16e/0x1b0 -24 unix_table_lock 47 [<ffffffff8150b111>] unix_release_sock+0x31/0x250 -25 unix_table_lock 15 [<ffffffff8150ca37>] unix_find_other+0x117/0x230 -26 unix_table_lock 5 [<ffffffff8150a09f>] unix_autobind+0x11f/0x1b0 -27 --------------- -28 unix_table_lock 39 [<ffffffff8150b111>] unix_release_sock+0x31/0x250 -29 unix_table_lock 49 [<ffffffff8150ad8e>] unix_create1+0x16e/0x1b0 -30 unix_table_lock 20 [<ffffffff8150ca37>] unix_find_other+0x117/0x230 -31 unix_table_lock 4 [<ffffffff8150a09f>] unix_autobind+0x11f/0x1b0 - - -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. - -Lines 09-12 show the first 4 recorded contention points (the code -which tries to get the lock) and lines 14-17 show the first 4 recorded -contended points (the lock holder). It is possible that the max -con-bounces point is missing in the statistics. - -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 7.91 97454 3453404 0.00 401.11 13224683.11 3.82 -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: 1526 11488 0.33 388.73 136294.31 11.86 21461 38404 0.00 37.93 109388.53 2.84 -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 - clockevents_lock: 2926159 2947636 0.15 46882.81 1784540466.34 605.41 3381345 3879161 0.00 2260.97 53178395.68 13.71 - tick_broadcast_lock: 346460 346717 0.18 2257.43 39364622.71 113.54 3642919 4242696 0.00 2263.79 49173646.60 11.59 - &mapping->i_mmap_mutex: 203896 203899 3.36 645530.05 31767507988.39 155800.21 3361776 8893984 0.17 2254.15 14110121.02 1.59 - &rq->lock: 135014 136909 0.18 606.09 842160.68 6.15 1540728 10436146 0.00 728.72 17606683.41 1.69 - &(&zone->lru_lock)->rlock: 93000 94934 0.16 59.18 188253.78 1.98 1199912 3809894 0.15 391.40 3559518.81 0.93 - tasklist_lock-W: 40667 41130 0.23 1189.42 428980.51 10.43 270278 510106 0.16 653.51 3939674.91 7.72 - tasklist_lock-R: 21298 21305 0.20 1310.05 215511.12 10.12 186204 241258 0.14 1162.33 1179779.23 4.89 - rcu_node_1: 47656 49022 0.16 635.41 193616.41 3.95 844888 1865423 0.00 764.26 1656226.96 0.89 - &(&dentry->d_lockref.lock)->rlock: 39791 40179 0.15 1302.08 88851.96 2.21 2790851 12527025 0.10 1910.75 3379714.27 0.27 - rcu_node_0: 29203 30064 0.16 786.55 1555573.00 51.74 88963 244254 0.00 398.87 428872.51 1.76 - -Clear the statistics: - -# echo 0 > /proc/lock_stat |