log: avoid stack lookups when not needed/used

log/logger.go

@@ -177,19 +177,22 @@ type logger struct {
 }
 
 func (l *logger) write(msg string, lvl Lvl, ctx []interface{}, skip int) {
-	l.h.Log(&Record{
+	record := &Record{
 		Time: time.Now(),
 		Lvl:  lvl,
 		Msg:  msg,
 		Ctx:  newContext(l.ctx, ctx),
-		Call: stack.Caller(skip),
 		KeyNames: RecordKeyNames{
 			Time: timeKey,
 			Msg:  msgKey,
 			Lvl:  lvlKey,
 			Ctx:  ctxKey,
 		},
-	})
+	}
+	if locationEnabled.Load() {
+		record.Call = stack.Caller(skip)
+	}
+	l.h.Log(record)
 }
 
 func (l *logger) New(ctx ...interface{}) Logger {

log/logger_test.go

@@ -0,0 +1,14 @@
+package log
+
+import (
+	"os"
+	"testing"
+)
+
+func BenchmarkTraceLogging(b *testing.B) {
+	Root().SetHandler(LvlFilterHandler(LvlInfo, StreamHandler(os.Stderr, TerminalFormat(true))))
+	b.ResetTimer()
+	for i := 0; i < b.N; i++ {
+		Trace("a message", "v", i)
+	}
+}