catalog: add benchmarks for overridden path comparison

Signed-off-by: Stephen J Day <stephen.day@docker.com>

registry/storage/catalog.go

@@ -108,6 +108,10 @@ func lessPath(a, b string) bool {
 // compareReplaceInline modifies runtime.cmpstring to replace old with new
 // during a byte-wise comparison.
 func compareReplaceInline(s1, s2 string, old, new byte) int {
+	// TODO(stevvooe): We are missing an optimization when the s1 and s2 have
+	// the exact same slice header. It will make the code unsafe but can
+	// provide some extra performance.
+
 	l := len(s1)
 	if len(s2) < l {
 		l = len(s2)

registry/storage/catalog_test.go

@@ -3,6 +3,7 @@ package storage
 import (
 	"fmt"
 	"io"
+	"math/rand"
 	"testing"
 
 	"github.com/docker/distribution"
@@ -220,3 +221,83 @@ func TestCatalogWalkError(t *testing.T) {
 		t.Errorf("Expected catalog driver list error")
 	}
 }
+
+func BenchmarkPathCompareEqual(B *testing.B) {
+	B.StopTimer()
+	pp := randomPath(100)
+	// make a real copy
+	ppb := append([]byte{}, []byte(pp)...)
+	a, b := pp, string(ppb)
+
+	B.StartTimer()
+	for i := 0; i < B.N; i++ {
+		lessPath(a, b)
+	}
+}
+
+func BenchmarkPathCompareNotEqual(B *testing.B) {
+	B.StopTimer()
+	a, b := randomPath(100), randomPath(100)
+	B.StartTimer()
+
+	for i := 0; i < B.N; i++ {
+		lessPath(a, b)
+	}
+}
+
+func BenchmarkPathCompareNative(B *testing.B) {
+	B.StopTimer()
+	a, b := randomPath(100), randomPath(100)
+	B.StartTimer()
+
+	for i := 0; i < B.N; i++ {
+		c := a < b
+		c = c && false
+	}
+}
+
+func BenchmarkPathCompareNativeEqual(B *testing.B) {
+	B.StopTimer()
+	pp := randomPath(100)
+	a, b := pp, pp
+	B.StartTimer()
+
+	for i := 0; i < B.N; i++ {
+		c := a < b
+		c = c && false
+	}
+}
+
+var filenameChars = []byte("abcdefghijklmnopqrstuvwxyz0123456789")
+var separatorChars = []byte("._-")
+
+func randomPath(length int64) string {
+	path := "/"
+	for int64(len(path)) < length {
+		chunkLength := rand.Int63n(length-int64(len(path))) + 1
+		chunk := randomFilename(chunkLength)
+		path += chunk
+		remaining := length - int64(len(path))
+		if remaining == 1 {
+			path += randomFilename(1)
+		} else if remaining > 1 {
+			path += "/"
+		}
+	}
+	return path
+}
+
+func randomFilename(length int64) string {
+	b := make([]byte, length)
+	wasSeparator := true
+	for i := range b {
+		if !wasSeparator && i < len(b)-1 && rand.Intn(4) == 0 {
+			b[i] = separatorChars[rand.Intn(len(separatorChars))]
+			wasSeparator = true
+		} else {
+			b[i] = filenameChars[rand.Intn(len(filenameChars))]
+			wasSeparator = false
+		}
+	}
+	return string(b)
+}