Commit-ID: 1222109a53637f96c581224198b86856d503f892
Gitweb: https://git.kernel.org/tip/1222109a53637f96c581224198b86856d503f892
Author: Waiman Long <longman@xxxxxxxxxx>
AuthorDate: Tue, 16 Oct 2018 09:45:06 -0400
Committer: Ingo Molnar <mingo@xxxxxxxxxx>
CommitDate: Wed, 17 Oct 2018 08:37:31 +0200
locking/qspinlock_stat: Count instances of nested lock slowpaths
Queued spinlock supports up to 4 levels of lock slowpath nesting -
user context, soft IRQ, hard IRQ and NMI. However, we are not sure how
often the nesting happens.
So add 3 more per-CPU stat counters to track the number of instances where
nesting index goes to 1, 2 and 3 respectively.
On a dual-socket 64-core 128-thread Zen server, the following were the
new stat counter values under different circumstances:
State slowpath index1 index2 index3
----- -------- ------ ------ -------
After bootup 1,012,150 82 0 0
After parallel build + perf-top 125,195,009 82 0 0
So the chance of having more than 2 levels of nesting is extremely low.
[ mingo: Minor changelog edits. ]
Signed-off-by: Waiman Long <longman@xxxxxxxxxx>
Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Cc: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Cc: Paul E. McKenney <paulmck@xxxxxxxxxxxxxxxxxx>
Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Cc: Will Deacon <will.deacon@xxxxxxx>
Link: http://lkml.kernel.org/r/1539697507-28084-1-git-send-email-longman@xxxxxxxxxx
Signed-off-by: Ingo Molnar <mingo@xxxxxxxxxx>
---
kernel/locking/qspinlock.c | 5 +++++
kernel/locking/qspinlock_stat.h | 6 ++++++
2 files changed, 11 insertions(+)
diff --git a/kernel/locking/qspinlock.c b/kernel/locking/qspinlock.c
index 341ca666bc60..ce6af1ee2cac 100644
--- a/kernel/locking/qspinlock.c
+++ b/kernel/locking/qspinlock.c
@@ -396,6 +396,11 @@ pv_queue:
node += idx;
+ /*
+ * Keep counts of non-zero index values:
+ */
+ qstat_inc(qstat_lock_idx1 + idx - 1, idx);
+
/*
* Ensure that we increment the head node->count before initialising
* the actual node. If the compiler is kind enough to reorder these
diff --git a/kernel/locking/qspinlock_stat.h b/kernel/locking/qspinlock_stat.h
index 6bd78c0740fc..42d3d8dc8f49 100644
--- a/kernel/locking/qspinlock_stat.h
+++ b/kernel/locking/qspinlock_stat.h
@@ -55,6 +55,9 @@ enum qlock_stats {
qstat_pv_wait_node,
qstat_lock_pending,
qstat_lock_slowpath,
+ qstat_lock_idx1,
+ qstat_lock_idx2,
+ qstat_lock_idx3,
qstat_num, /* Total number of statistical counters */
qstat_reset_cnts = qstat_num,
};
@@ -82,6 +85,9 @@ static const char * const qstat_names[qstat_num + 1] = {
[qstat_pv_wait_node] = "pv_wait_node",
[qstat_lock_pending] = "lock_pending",
[qstat_lock_slowpath] = "lock_slowpath",
+ [qstat_lock_idx1] = "lock_index1",
+ [qstat_lock_idx2] = "lock_index2",
+ [qstat_lock_idx3] = "lock_index3",
[qstat_reset_cnts] = "reset_counters",
};
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