locking/qspinlock_stat: Track the no MCS node available case

mainline inclusion
from mainline-5.1-rc1
commit 412f34a8
category: bugfix
bugzilla: 13227
CVE: NA

-------------------------------------------------

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: NWaiman Long <longman@redhat.com>
Signed-off-by: NPeter 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.comSigned-off-by: NIngo Molnar <mingo@kernel.org>
Signed-off-by: NHanjun Guo <guohanjun@huawei.com>
Signed-off-by: NWei Li <liwei391@huawei.com>
Signed-off-by: NYang Yingliang <yangyingliang@huawei.com>

kernel/locking/qspinlock.c

@@ -416,6 +416,7 @@ 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;
@@ -426,7 +427,7 @@ 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

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",
 };