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Subject[PATCH v3 2/4] locking/qspinlock_stat: Track the no MCS node available case
Date
Track the number of slowpath locking operations that are being done
without any MCS node available as well renaming lock_index[123] to make
them more descriptive.

Using these stat counters is one way to find out if a code path is
being exercised.

Signed-off-by: Waiman Long <longman@redhat.com>
---
kernel/locking/qspinlock.c | 3 ++-
kernel/locking/qspinlock_stat.h | 21 +++++++++++++++------
2 files changed, 17 insertions(+), 7 deletions(-)

diff --git a/kernel/locking/qspinlock.c b/kernel/locking/qspinlock.c
index 0875053..21ee51b 100644
--- a/kernel/locking/qspinlock.c
+++ b/kernel/locking/qspinlock.c
@@ -422,6 +422,7 @@ void queued_spin_lock_slowpath(struct qspinlock *lock, u32 val)
* simple enough.
*/
if (unlikely(idx >= MAX_NODES)) {
+ qstat_inc(qstat_lock_no_node, true);
while (!queued_spin_trylock(lock))
cpu_relax();
goto release;
@@ -432,7 +433,7 @@ void queued_spin_lock_slowpath(struct qspinlock *lock, u32 val)
/*
* Keep counts of non-zero index values:
*/
- qstat_inc(qstat_lock_idx1 + idx - 1, idx);
+ qstat_inc(qstat_lock_use_node2 + idx - 1, idx);

/*
* Ensure that we increment the head node->count before initialising
diff --git a/kernel/locking/qspinlock_stat.h b/kernel/locking/qspinlock_stat.h
index 42d3d8d..365ce6d 100644
--- a/kernel/locking/qspinlock_stat.h
+++ b/kernel/locking/qspinlock_stat.h
@@ -30,6 +30,13 @@
* pv_wait_node - # of vCPU wait's at a non-head queue node
* lock_pending - # of locking operations via pending code
* lock_slowpath - # of locking operations via MCS lock queue
+ * lock_use_node2 - # of locking operations that use 2nd percpu node
+ * lock_use_node3 - # of locking operations that use 3rd percpu node
+ * lock_use_node4 - # of locking operations that use 4th percpu node
+ * lock_no_node - # of locking operations without using percpu node
+ *
+ * Subtracting lock_use_node[234] from lock_slowpath will give you
+ * lock_use_node1.
*
* Writing to the "reset_counters" file will reset all the above counter
* values.
@@ -55,9 +62,10 @@ enum qlock_stats {
qstat_pv_wait_node,
qstat_lock_pending,
qstat_lock_slowpath,
- qstat_lock_idx1,
- qstat_lock_idx2,
- qstat_lock_idx3,
+ qstat_lock_use_node2,
+ qstat_lock_use_node3,
+ qstat_lock_use_node4,
+ qstat_lock_no_node,
qstat_num, /* Total number of statistical counters */
qstat_reset_cnts = qstat_num,
};
@@ -85,9 +93,10 @@ enum qlock_stats {
[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_lock_use_node2] = "lock_use_node2",
+ [qstat_lock_use_node3] = "lock_use_node3",
+ [qstat_lock_use_node4] = "lock_use_node4",
+ [qstat_lock_no_node] = "lock_no_node",
[qstat_reset_cnts] = "reset_counters",
};

--
1.8.3.1
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