136 lines
7.9 KiB
Plaintext
136 lines
7.9 KiB
Plaintext
|
|
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. 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
|
|
|
|
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.
|
|
|
|
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_lock: 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
|