linux-kernel - [tip:locking/core] locking/qspinlock_stat: Track the no MCS node available case

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Message-ID: <tip-412f34a82ccf7dd52f6b197f6450a33f03342523@git.kernel.org>
Date:   Mon, 4 Feb 2019 00:58:52 -0800
From:   tip-bot for Waiman Long <tipbot@...or.com>
To:     linux-tip-commits@...r.kernel.org
Cc:     bp@...en8.de, peterz@...radead.org, torvalds@...ux-foundation.org,
        paulmck@...ux.vnet.ibm.com, hpa@...or.com, james.morse@....com,
        longman@...hat.com, zhenzhong.duan@...cle.com, will.deacon@....com,
        mingo@...nel.org, akpm@...ux-foundation.org,
        srinivas.eeda@...cle.com, linux-kernel@...r.kernel.org,
        tglx@...utronix.de
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@...hat.com>
AuthorDate: Tue, 29 Jan 2019 22:53:46 +0100
Committer:  Ingo Molnar <mingo@...nel.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@...hat.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
Cc: Andrew Morton <akpm@...ux-foundation.org>
Cc: Borislav Petkov <bp@...en8.de>
Cc: H. Peter Anvin <hpa@...or.com>
Cc: James Morse <james.morse@....com>
Cc: Linus Torvalds <torvalds@...ux-foundation.org>
Cc: Paul E. McKenney <paulmck@...ux.vnet.ibm.com>
Cc: Peter Zijlstra <peterz@...radead.org>
Cc: SRINIVAS <srinivas.eeda@...cle.com>
Cc: Thomas Gleixner <tglx@...utronix.de>
Cc: Will Deacon <will.deacon@....com>
Cc: Zhenzhong Duan <zhenzhong.duan@...cle.com>
Link: https://lkml.kernel.org/r/1548798828-16156-3-git-send-email-longman@redhat.com
Signed-off-by: Ingo Molnar <mingo@...nel.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",
 };