Linux Kernel 当前运行中 锁的状态信息

Linux Kernel 当前运行中 锁的状态信息

Linux Kernel 当前运行中 锁的状态信息【适用于调试模式】。

俺的设备死机的时候，发现是因为锁导致的，这时候相当郁闷的是没地方看系统相关锁的信息，当找到内核文档下的相关信息后，

大惊：原来开发者已经为俺考虑好这些东东了：进入调试模式就是这么简单：

锁统计信息信息
LOCK STATISTICS

- WHY
锁竞争会严重地影响性能和表现
Because things like lock contention can severely impact performance.

- HOW
如何实现

Lockdep already has hooks in the lock functions and maps lock instances to
lock classes. We build on that. 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.

 - USAGE

Look at the current lock statistics:

( line numbers not part of actual output, done for clarity in the explanation
  below )

# less /proc/lock_stat

1. 01 lock_stat version 0.3  
2. 02 -----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------  
3. 03                               class name    con-bounces    contentions   waittime-min   waittime-max waittime-total    acq-bounces   acquisitions   holdtime-min   holdtime-max holdtime-total  
4. 04 -----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------  
5. 05  
6. 06                          &mm->mmap_sem-W:           233            538 18446744073708       22924.27      607243.51           1342          45806           1.71        8595.89     1180582.34  
7. 07                          &mm->mmap_sem-R:           205            587 18446744073708       28403.36      731975.00           1940         412426           0.58      187825.45     6307502.88  
8. 08                          ---------------  
9. 09                            &mm->mmap_sem            487          [<ffffffff8053491f>] do_page_fault+0x466/0x928  
10. 10                            &mm->mmap_sem            179          [<ffffffff802a6200>] sys_mprotect+0xcd/0x21d  
11. 11                            &mm->mmap_sem            279          [<ffffffff80210a57>] sys_mmap+0x75/0xce  
12. 12                            &mm->mmap_sem             76          [<ffffffff802a490b>] sys_munmap+0x32/0x59  
13. 13                          ---------------  
14. 14                            &mm->mmap_sem            270          [<ffffffff80210a57>] sys_mmap+0x75/0xce  
15. 15                            &mm->mmap_sem            431          [<ffffffff8053491f>] do_page_fault+0x466/0x928  
16. 16                            &mm->mmap_sem            138          [<ffffffff802a490b>] sys_munmap+0x32/0x59  
17. 17                            &mm->mmap_sem            145          [<ffffffff802a6200>] sys_mprotect+0xcd/0x21d  
18. 18  
19. 19 ...............................................................................................................................................................................................  
20. 20  
21. 21                              dcache_lock:           621            623           0.52         118.26        1053.02           6745          91930           0.29         316.29      118423.41  
22. 22                              -----------  
23. 23                              dcache_lock            179          [<ffffffff80378274>] _atomic_dec_and_lock+0x34/0x54  
24. 24                              dcache_lock            113          [<ffffffff802cc17b>] d_alloc+0x19a/0x1eb  
25. 25                              dcache_lock             99          [<ffffffff802ca0dc>] d_rehash+0x1b/0x44  
26. 26                              dcache_lock            104          [<ffffffff802cbca0>] d_instantiate+0x36/0x8a  
27. 27                              -----------  
28. 28                              dcache_lock            192          [<ffffffff80378274>] _atomic_dec_and_lock+0x34/0x54  
29. 29                              dcache_lock             98          [<ffffffff802ca0dc>] d_rehash+0x1b/0x44  
30. 30                              dcache_lock             72          [<ffffffff802cc17b>] d_alloc+0x19a/0x1eb  
31. 31                              dcache_lock            112          [<ffffffff802cbca0>] d_instantiate+0x36/0x8a