performance: precompile regex before iterating

entry.go

@@ -96,6 +96,11 @@ func getCaller() (method string) {
 	// Restrict the lookback to 25 frames - if it's further than that, report UNKNOWN
 	pcs := make([]uintptr, 25)
 
+	matchesLogrus, err := regexp.Compile("logrus.*")
+	if err != nil {
+		return "CALLER_LOOKUP_FAILED"
+	}
+
 	// the first non-logrus caller is at least three frames away
 	depth := runtime.Callers(3, pcs)
 	for i := 0; i < depth; i++ {
@@ -105,10 +110,7 @@ func getCaller() (method string) {
 			fullFuncName = fullFuncName[idx:]
 		}
 
-		matched, err := regexp.MatchString("logrus.*", fullFuncName)
+		matched := matchesLogrus.MatchString(fullFuncName)
-		if err != nil {
-			return "CALLER_LOOKUP_FAILED"
-		}
 
 		// If the caller isn't part of logrus, we're done
 		if !matched {