Documentation/locking/lockstat.rst
As the name suggests, it provides statistics on locks.
Because things like lock contention can severely impact performance.
Lockdep already has hooks in the lock functions and maps lock instances to lock classes. We build on that (see Documentation/locking/lockdep-design.rst). 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.
Lock statistics are enabled via CONFIG_LOCK_STAT.
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 )
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::
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::