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Subject[PATCH] Documentation: statistics about nested locks
Hi all,
just a little patch to the Documentation. I had some trouble
understanding the trailing "/1" on some lock class names of lock_stat
output, so I added something on this inside lockstat documentation.

Signed-off-by: Juri Lelli <juri.lelli@gmail.com>

---
Documentation/lockstat.txt | 36 ++++++++++++++++++++++++++++++++++--
1 files changed, 34 insertions(+), 2 deletions(-)

diff --git a/Documentation/lockstat.txt b/Documentation/lockstat.txt
index 65f4c79..75eeb65 100644
--- a/Documentation/lockstat.txt
+++ b/Documentation/lockstat.txt
@@ -12,8 +12,9 @@ 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.
+lock classes. We build on that (see Documentation/lockdep-design.txt).
+The graph below shows the relation between the lock functions and the
various
+hooks therein.

__acquire
|
@@ -128,6 +129,37 @@ 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 97454
3453404 0.00 401.11 13224683.11
+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: 11526
11488 0.33 388.73 136294.31 21461
38404 0.00 37.93 109388.53
+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 first subclass (/1) of &rq->lock
class, 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
--
1.7.4.1

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