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Subject[PATCH 2/5] 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 | 4 +++-
kernel/locking/qspinlock_stat.h | 24 ++++++++++++++++++------
2 files changed, 21 insertions(+), 7 deletions(-)

diff --git a/kernel/locking/qspinlock.c b/kernel/locking/qspinlock.c
index 5bb06df..8163633 100644
--- a/kernel/locking/qspinlock.c
+++ b/kernel/locking/qspinlock.c
@@ -395,6 +395,7 @@ static noinline void acquire_lock_no_node(struct qspinlock *lock)
*/
static noinline void spin_on_waiting(struct qspinlock *lock)
{
+ qstat_inc(qstat_lock_waiting, true);
atomic_cond_read_relaxed(&lock->val, !(VAL & _Q_WAITING_VAL));

/* Clear the pending bit now */
@@ -548,6 +549,7 @@ void queued_spin_lock_slowpath(struct qspinlock *lock, u32 val)
*/
if (unlikely(idx >= MAX_NODES)) {
acquire_lock_no_node(lock);
+ qstat_inc(qstat_lock_no_node, true);
goto release;
}

@@ -556,7 +558,7 @@ 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..4f8ca8c 100644
--- a/kernel/locking/qspinlock_stat.h
+++ b/kernel/locking/qspinlock_stat.h
@@ -30,6 +30,14 @@
* 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
+ * lock_waiting - # of locking operations with waiting bit set
+ *
+ * Subtraccting 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 +63,11 @@ 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_lock_waiting,
qstat_num, /* Total number of statistical counters */
qstat_reset_cnts = qstat_num,
};
@@ -85,9 +95,11 @@ 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_lock_waiting] = "lock_waiting",
[qstat_reset_cnts] = "reset_counters",
};

--
1.8.3.1
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