Do not copy PathElems when creating a map value's path. (#609)

Before
BenchmarkNotificationOutput-12                     10000            107130 ns/op
BenchmarkNotificationOutputElement-12              14344             83329 ns/op

After
BenchmarkNotificationOutput-12                     12613             95651 ns/op
BenchmarkNotificationOutputElement-12              14298             84451 ns/op

Author: wenovus

ygot/render.go

@@ -462,13 +462,14 @@ func findUpdatedLeaves(leaves map[*path]interface{}, s GoStruct, parent *gnmiPat
 // key and value. The format of the path returned depends on the input format
 // of the parentPath.
 func mapValuePath(key, value reflect.Value, parentPath *gnmiPath) (*gnmiPath, error) {
-	childPath := &gnmiPath{}
+	var childPath *gnmiPath
 
 	if parentPath == nil {
 		return nil, fmt.Errorf("nil map paths supplied to mapValuePath for %v %v", key.Interface(), value.Interface())
 	}
 
 	if parentPath.isStringSlicePath() {
+		childPath = &gnmiPath{}
 		keyval, err := KeyValueAsString(key.Interface())
 		if err != nil {
 			return nil, fmt.Errorf("can't append path element key: %v", err)
@@ -480,10 +481,8 @@ func mapValuePath(key, value reflect.Value, parentPath *gnmiPath) (*gnmiPath, er
 		return childPath, nil
 	}
 
-	for _, e := range parentPath.pathElemPath {
-		n := proto.Clone(e).(*gnmipb.PathElem)
-		childPath.pathElemPath = append(childPath.pathElemPath, n)
-	}
+	// Only the pointer values are copied for performance.
+	childPath = parentPath.Copy()
 
 	return appendgNMIPathElemKey(value, childPath)
 }

ygot/schema_tests/schema_test.go

@@ -490,3 +490,38 @@ func TestNotificationOutput(t *testing.T) {
 		})
 	}
 }
+
+func getBenchmarkDevice() *exampleoc.Device {
+	intfs := []string{"eth0", "eth1", "eth2", "eth3"}
+	d := &exampleoc.Device{}
+	for _, intf := range intfs {
+		d.GetOrCreateInterface(intf)
+		is := d.GetOrCreateLldp().GetOrCreateInterface(intf).GetOrCreateNeighbor("neighbor")
+		is.LastUpdate = ygot.Int64(42)
+	}
+	return d
+}
+
+func BenchmarkNotificationOutput(b *testing.B) {
+	d := getBenchmarkDevice()
+	b.ResetTimer()
+	for i := 0; i != b.N; i++ {
+		if _, err := ygot.TogNMINotifications(d, 0, ygot.GNMINotificationsConfig{
+			UsePathElem: true,
+		}); err != nil {
+			b.Fatalf("cannot marshal input to gNMI Notifications, %v", err)
+		}
+	}
+}
+
+func BenchmarkNotificationOutputElement(b *testing.B) {
+	d := getBenchmarkDevice()
+	b.ResetTimer()
+	for i := 0; i != b.N; i++ {
+		if _, err := ygot.TogNMINotifications(d, 0, ygot.GNMINotificationsConfig{
+			UsePathElem: false,
+		}); err != nil {
+			b.Fatalf("cannot marshal input to gNMI Notifications, %v", err)
+		}
+	}
+}