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Subject[tip:locking/core] locking/qspinlock_stat: Track the no MCS node available case
Commit-ID:  412f34a82ccf7dd52f6b197f6450a33f03342523
Gitweb: https://git.kernel.org/tip/412f34a82ccf7dd52f6b197f6450a33f03342523
Author: Waiman Long <longman@redhat.com>
AuthorDate: Tue, 29 Jan 2019 22:53:46 +0100
Committer: Ingo Molnar <mingo@kernel.org>
CommitDate: Mon, 4 Feb 2019 09:03:30 +0100

locking/qspinlock_stat: Track the no MCS node available case

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>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Borislav Petkov <bp@alien8.de>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: James Morse <james.morse@arm.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: SRINIVAS <srinivas.eeda@oracle.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Will Deacon <will.deacon@arm.com>
Cc: Zhenzhong Duan <zhenzhong.duan@oracle.com>
Link: https://lkml.kernel.org/r/1548798828-16156-3-git-send-email-longman@redhat.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
---
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 0875053c4050..21ee51b47961 100644
--- a/kernel/locking/qspinlock.c
+++ b/kernel/locking/qspinlock.c
@@ -422,6 +422,7 @@ pv_queue:
* 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 @@ pv_queue:
/*
* 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 42d3d8dc8f49..d73f85388d5c 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 per-CPU node
+ * lock_use_node3 - # of locking operations that use 3rd per-CPU node
+ * lock_use_node4 - # of locking operations that use 4th per-CPU node
+ * lock_no_node - # of locking operations without using per-CPU 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 @@ 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_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",
};

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