Fix a bug in UMTX_PROFILING:

UMTX_PROFILING should really analyze the distribution of locks as they
index entries in the umtxq_chains hash-table.
However, the current implementation does add/dec the length counters
for *every* thread insert/removal, measuring at all really userland
contention and not the hash distribution.

Fix this by correctly add/dec the length counters in the points where
it is really needed.

Please note that this bug brought us questioning in the past the quality
of the umtx hash table distribution.
To date with all the benchmarks I could try I was not able to reproduce
any issue about the hash distribution on umtx.

Sponsored by:	EMC / Isilon storage division
Reviewed by:	jeff, davide
MFC after:	2 weeks

1 files changed, 11 insertions, 11 deletions

diff --git a/sys/kern/kern_umtx.c b/sys/kern/kern_umtx.c
index f50a6f9..6026b80 100644
--- a/sys/kern/kern_umtx.c
+++ b/sys/kern/kern_umtx.c
@@ -542,19 +542,19 @@ umtxq_insert_queue(struct umtx_q *uq, int q)
 		uh = uq->uq_spare_queue;
 		uh->key = uq->uq_key;
 		LIST_INSERT_HEAD(&uc->uc_queue[q], uh, link);
+#ifdef UMTX_PROFILING
+		uc->length++;
+		if (uc->length > uc->max_length) {
+			uc->max_length = uc->length;
+			if (uc->max_length > max_length)
+				max_length = uc->max_length;	
+		}
+#endif
 	}
 	uq->uq_spare_queue = NULL;
 
 	TAILQ_INSERT_TAIL(&uh->head, uq, uq_link);
 	uh->length++;
-#ifdef UMTX_PROFILING
-	uc->length++;
-	if (uc->length > uc->max_length) {
-		uc->max_length = uc->length;
-		if (uc->max_length > max_length)
-			max_length = uc->max_length;	
-	}
-#endif
 	uq->uq_flags |= UQF_UMTXQ;
 	uq->uq_cur_queue = uh;
 	return;
@@ -572,13 +572,13 @@ umtxq_remove_queue(struct umtx_q *uq, int q)
 		uh = uq->uq_cur_queue;
 		TAILQ_REMOVE(&uh->head, uq, uq_link);
 		uh->length--;
-#ifdef UMTX_PROFILING
-		uc->length--;
-#endif
 		uq->uq_flags &= ~UQF_UMTXQ;
 		if (TAILQ_EMPTY(&uh->head)) {
 			KASSERT(uh->length == 0,
 			    ("inconsistent umtxq_queue length"));
+#ifdef UMTX_PROFILING
+			uc->length--;
+#endif
 			LIST_REMOVE(uh, link);
 		} else {
 			uh = LIST_FIRST(&uc->uc_spare_queue);