mirror of
https://mirrors.bfsu.edu.cn/git/linux.git
synced 2024-11-11 04:18:39 +08:00
lockstat: documentation
Provide some documentation for CONFIG_LOCK_STAT. Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl> Acked-by: Ingo Molnar <mingo@elte.hu> Cc: "Randy.Dunlap" <rdunlap@xenotime.net> Cc: Rob Landley <rob@landley.net> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Peter Zijlstra
Linus Torvalds
parent
52a2638bff
commit
a560aa48ee
120
Documentation/lockstat.txt
Normal file
120
Documentation/lockstat.txt
Normal file
@ -0,0 +1,120 @@
|
||||
|
||||
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 0.2
|
||||
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 &inode->i_data.tree_lock-W: 15 21657 0.18 1093295.30 11547131054.85 58 10415 0.16 87.51 6387.60
|
||||
07 &inode->i_data.tree_lock-R: 0 0 0.00 0.00 0.00 23302 231198 0.25 8.45 98023.38
|
||||
08 --------------------------
|
||||
09 &inode->i_data.tree_lock 0 [<ffffffff8027c08f>] add_to_page_cache+0x5f/0x190
|
||||
10
|
||||
11 ...............................................................................................................................................................................................
|
||||
12
|
||||
13 dcache_lock: 1037 1161 0.38 45.32 774.51 6611 243371 0.15 306.48 77387.24
|
||||
14 -----------
|
||||
15 dcache_lock 180 [<ffffffff802c0d7e>] sys_getcwd+0x11e/0x230
|
||||
16 dcache_lock 165 [<ffffffff802c002a>] d_alloc+0x15a/0x210
|
||||
17 dcache_lock 33 [<ffffffff8035818d>] _atomic_dec_and_lock+0x4d/0x70
|
||||
18 dcache_lock 1 [<ffffffff802beef8>] shrink_dcache_parent+0x18/0x130
|
||||
|
||||
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 05-10 and 13-18 show the actual
|
||||
statistics. These statistics come in two parts; the actual stats separated by a
|
||||
short separator (line 08, 14) from the contention points.
|
||||
|
||||
The first lock (05-10) 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.
|
||||
|
||||
|
||||
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
|
||||
@ -294,6 +294,8 @@ config LOCK_STAT
|
||||
help
|
||||
This feature enables tracking lock contention points
|
||||
|
||||
For more details, see Documentation/lockstat.txt
|
||||
|
||||
config DEBUG_LOCKDEP
|
||||
bool "Lock dependency engine debugging"
|
||||
depends on DEBUG_KERNEL && LOCKDEP
|
||||
|
||||
Loading…
Reference in New Issue
Block a user