logs benchmark: really write through pipe

While the benchmark is focused on encoding, it becomes a bit more realistic
when actually passing the encoded data to the Linux kernel. Features like
output buffering are more likely to have a visible effect when invoking
syscalls.

test/integration/logs/benchmark/benchmark_test.go

@@ -74,14 +74,16 @@ func BenchmarkEncoding(b *testing.B) {
 				state := klog.CaptureState()
 				defer state.Restore()
 
-				var output bytesWritten
+				// To make the tests a bit more realistic, at
+				// least do system calls during each write.
+				output := newBytesWritten(b, "/dev/null")
 				c := logsapi.NewLoggingConfiguration()
 				c.Format = format
 				o := logsapi.LoggingOptions{
-					ErrorStream: &output,
-					InfoStream:  &output,
+					ErrorStream: output,
+					InfoStream:  output,
 				}
-				klog.SetOutput(&output)
+				klog.SetOutput(output)
 				defer func() {
 					if err := logsapi.ResetForTest(nil); err != nil {
 						b.Errorf("error resetting logsapi: %v", err)
@@ -108,7 +110,7 @@ func BenchmarkEncoding(b *testing.B) {
 				// Report messages/s instead of ns/op because "op" varies.
 				b.ReportMetric(0, "ns/op")
 				b.ReportMetric(float64(total)/duration.Seconds(), "msgs/s")
-				fileSizes[filepath.Base(b.Name())] = int(output)
+				fileSizes[filepath.Base(b.Name())] = int(output.bytesWritten)
 			}
 
 			b.Run("printf", func(b *testing.B) {

test/integration/logs/benchmark/common_test.go

@@ -18,6 +18,8 @@ package benchmark
 
 import (
 	"flag"
+	"os"
+	"testing"
 
 	"k8s.io/klog/v2"
 )
@@ -34,12 +36,25 @@ func init() {
 	flag.Set("stderrthreshold", "FATAL")
 }
 
-type bytesWritten int64
+func newBytesWritten(tb testing.TB, filename string) *bytesWritten {
+	out, err := os.Create(filename)
+	if err != nil {
+		tb.Fatalf("open fake output: %v", err)
+	}
+	tb.Cleanup(func() { _ = out.Close() })
+	return &bytesWritten{
+		out: out,
+	}
+}
+
+type bytesWritten struct {
+	out          *os.File
+	bytesWritten int64
+}
 
 func (b *bytesWritten) Write(data []byte) (int, error) {
-	l := len(data)
-	*b += bytesWritten(l)
-	return l, nil
+	b.bytesWritten += int64(len(data))
+	return b.out.Write(data)
 }
 
 func printf(item logMessage) {