ofproto: Avoid extra O(N) work in common case on flow addition.

The OpenFlow OFPFF_CHECK_OVERLAP flag requires us to check whether the flow
being inserted overlaps with any existing flows.  That isn't efficiently
implemented and typically requires us to compare the new flow against most
or all of the existing flows.  We don't have to do that work if
OFPFF_CHECK_OVERLAP is not requested, but commit 0b4f207828c (classifier:
Make use of the classifier thread safe.) inadvertently made us do it
anyway.

Signed-off-by: Ben Pfaff <blp@nicira.com>
Acked-by: Ethan Jackson <ethan@nicira.com>

diff --git a/ofproto/ofproto.c b/ofproto/ofproto.c
index bead3c4..c8edb2d 100644 (file)
--- a/ofproto/ofproto.c
+++ b/ofproto/ofproto.c
@@ -3359,7 +3359,6 @@ add_flow(struct ofproto *ofproto, struct ofconn *ofconn,
     struct rule *victim;
     struct rule *rule;
     uint8_t table_id;
-    bool overlaps;
     int error;
 
     error = check_table_id(ofproto, fm->table_id);
@@ -3416,13 +3415,18 @@ add_flow(struct ofproto *ofproto, struct ofconn *ofconn,
     }
 
     /* Check for overlap, if requested. */
-    ovs_rwlock_rdlock(&table->cls.rwlock);
-    overlaps = classifier_rule_overlaps(&table->cls, &rule->cr);
-    ovs_rwlock_unlock(&table->cls.rwlock);
-    if (fm->flags & OFPFF_CHECK_OVERLAP && overlaps) {
-        cls_rule_destroy(&rule->cr);
-        ofproto->ofproto_class->rule_dealloc(rule);
-        return OFPERR_OFPFMFC_OVERLAP;
+    if (fm->flags & OFPFF_CHECK_OVERLAP) {
+        bool overlaps;
+
+        ovs_rwlock_rdlock(&table->cls.rwlock);
+        overlaps = classifier_rule_overlaps(&table->cls, &rule->cr);
+        ovs_rwlock_unlock(&table->cls.rwlock);
+
+        if (overlaps) {
+            cls_rule_destroy(&rule->cr);
+            ofproto->ofproto_class->rule_dealloc(rule);
+            return OFPERR_OFPFMFC_OVERLAP;
+        }
     }
 
     /* FIXME: Implement OFPFF12_RESET_COUNTS */