aboutsummaryrefslogtreecommitdiffstats
path: root/Documentation/locking/lockstat.txt
blob: 568bbbacee91a581e1bb4be9bd54ed7e73d830e1 (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
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/lokcing/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
19                           &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

Privacy Policy