Add a benchmark for addExtraLabels function

push_test.go

@@ -26,7 +26,7 @@ bar{foo="bar",a="x"} 2
 foo 1
 # some counter
 # type foobar counter
-foobar{a="b",c="d"} 4`, `x="y"`, `foo{x="y"} 1
+	  foobar{a="b",c="d"} 4`, `x="y"`, `foo{x="y"} 1
 # some counter
 # type foobar counter
 foobar{x="y",a="b",c="d"} 4

push_timing_test.go

@@ -0,0 +1,20 @@
+package metrics
+
+import (
+	"testing"
+)
+
+func BenchmarkAddExtraLabels(b *testing.B) {
+	extraLabels := `foo="bar"`
+	src := []byte(`foo 1
+bar{baz="x"} 2
+`)
+	b.ReportAllocs()
+	b.SetBytes(1)
+	b.RunParallel(func(pb *testing.PB) {
+		var dst []byte
+		for pb.Next() {
+			dst = addExtraLabels(dst[:0], src, extraLabels)
+		}
+	})
+}