Improved FormatMap: Improves performance by about 4x, or nearly 2x in the worst case (#112661)

* Improved FormatMap

Improves performance by about 4x, or nearly 2x in the worst case

old FormatMap
BenchmarkFormatMap-12             873046                1238 ns/op             384 B/op         13 allocs/op
new FormatMap
BenchmarkFormatMap-12            3665762               327.0 ns/op             152 B/op          3 allocs/op

Signed-off-by: aimuz <mr.imuz@gmail.com>

* fixed

Signed-off-by: aimuz <mr.imuz@gmail.com>

* fixed

Signed-off-by: aimuz <mr.imuz@gmail.com>

* test: fix test

Signed-off-by: aimuz <mr.imuz@gmail.com>

---------

Signed-off-by: aimuz <mr.imuz@gmail.com>

pkg/fieldpath/fieldpath.go

@@ -18,26 +18,36 @@ package fieldpath
 
 import (
 	"fmt"
+	"sort"
+	"strconv"
 	"strings"
 
 	"k8s.io/apimachinery/pkg/api/meta"
-	"k8s.io/apimachinery/pkg/util/sets"
 	"k8s.io/apimachinery/pkg/util/validation"
 )
 
 // FormatMap formats map[string]string to a string.
 func FormatMap(m map[string]string) (fmtStr string) {
 	// output with keys in sorted order to provide stable output
-	keys := sets.NewString()
+	keys := make([]string, 0, len(m))
-	for key := range m {
+	var grow int
-		keys.Insert(key)
+	for k, v := range m {
+		keys = append(keys, k)
+		// why add 4: (for =, \n, " and ")
+		grow += len(k) + len(v) + 4
 	}
-	for _, key := range keys.List() {
+	sort.Strings(keys)
-		fmtStr += fmt.Sprintf("%v=%q\n", key, m[key])
+	// allocate space to avoid expansion
+	dst := make([]byte, 0, grow)
+	for _, key := range keys {
+		if len(dst) > 0 {
+			dst = append(dst, '\n')
+		}
+		dst = append(dst, key...)
+		dst = append(dst, '=')
+		dst = strconv.AppendQuote(dst, m[key])
 	}
-	fmtStr = strings.TrimSuffix(fmtStr, "\n")
+	return string(dst)
-
-	return
 }
 
 // ExtractFieldPathAsString extracts the field from the given object

pkg/fieldpath/fieldpath_test.go

@@ -24,6 +24,30 @@ import (
 	metav1 "k8s.io/apimachinery/pkg/apis/meta/v1"
 )
 
+func BenchmarkFormatMap(b *testing.B) {
+	var s string
+	m := map[string]string{
+		"spec.pod.beta.kubernetes.io/statefulset-index": "1",
+		"Www.k8s.io/test":                                        "1",
+		"foo":                                                    "bar",
+		"flannel.alpha.coreos.com/backend-data":                  `{"VNI":1,"VtepMAC":"ce:f9:c7:a4:de:64"}`,
+		"flannel.alpha.coreos.com/backend-type":                  "vxlan",
+		"flannel.alpha.coreos.com/kube-subnet-manager":           "true",
+		"flannel.alpha.coreos.com/public-ip":                     "192.168.19.160",
+		"management.cattle.io/pod-limits":                        `{"cpu":"11400m","memory":"7965Mi"}`,
+		"management.cattle.io/pod-requests":                      `{"cpu":"2482m","memory":"7984Mi","pods":"26"}`,
+		"node.alpha.kubernetes.io/ttl":                           "0",
+		"volumes.kubernetes.io/controller-managed-attach-detach": "true",
+	}
+	b.ReportAllocs()
+	b.ResetTimer()
+	for i := 0; i < b.N; i++ {
+		s = FormatMap(m)
+	}
+	// Avoid compiler optimizations
+	_ = s
+}
+
 func TestExtractFieldPathAsString(t *testing.T) {
 	cases := []struct {
 		name                    string
@@ -268,3 +292,72 @@ func TestSplitMaybeSubscriptedPath(t *testing.T) {
 		}
 	}
 }
+
+// TestFormatMap
+func TestFormatMap(t *testing.T) {
+	type args struct {
+		m map[string]string
+	}
+	tests := []struct {
+		name       string
+		args       args
+		wantFmtStr string
+	}{
+		{
+			name: "nil",
+			args: args{
+				m: nil,
+			},
+			wantFmtStr: "",
+		},
+		{
+			name: "label",
+			args: args{
+				m: map[string]string{
+					"beta.kubernetes.io/os":                 "linux",
+					"kubernetes.io/arch":                    "amd64",
+					"kubernetes.io/hostname":                "master01",
+					"kubernetes.io/os":                      "linux",
+					"node-role.kubernetes.io/control-plane": "true",
+					"node-role.kubernetes.io/master":        "true",
+				},
+			},
+			wantFmtStr: `beta.kubernetes.io/os="linux"
+kubernetes.io/arch="amd64"
+kubernetes.io/hostname="master01"
+kubernetes.io/os="linux"
+node-role.kubernetes.io/control-plane="true"
+node-role.kubernetes.io/master="true"`,
+		},
+		{
+			name: "annotation",
+			args: args{
+				m: map[string]string{
+					"flannel.alpha.coreos.com/backend-data":                  `{"VNI":1,"VtepMAC":"ce:f9:c7:a4:de:64"}`,
+					"flannel.alpha.coreos.com/backend-type":                  "vxlan",
+					"flannel.alpha.coreos.com/kube-subnet-manager":           "true",
+					"flannel.alpha.coreos.com/public-ip":                     "192.168.19.160",
+					"management.cattle.io/pod-limits":                        `{"cpu":"11400m","memory":"7965Mi"}`,
+					"management.cattle.io/pod-requests":                      `{"cpu":"2482m","memory":"7984Mi","pods":"26"}`,
+					"node.alpha.kubernetes.io/ttl":                           "0",
+					"volumes.kubernetes.io/controller-managed-attach-detach": "true",
+				},
+			},
+			wantFmtStr: `flannel.alpha.coreos.com/backend-data="{\"VNI\":1,\"VtepMAC\":\"ce:f9:c7:a4:de:64\"}"
+flannel.alpha.coreos.com/backend-type="vxlan"
+flannel.alpha.coreos.com/kube-subnet-manager="true"
+flannel.alpha.coreos.com/public-ip="192.168.19.160"
+management.cattle.io/pod-limits="{\"cpu\":\"11400m\",\"memory\":\"7965Mi\"}"
+management.cattle.io/pod-requests="{\"cpu\":\"2482m\",\"memory\":\"7984Mi\",\"pods\":\"26\"}"
+node.alpha.kubernetes.io/ttl="0"
+volumes.kubernetes.io/controller-managed-attach-detach="true"`,
+		},
+	}
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			if gotFmtStr := FormatMap(tt.args.m); gotFmtStr != tt.wantFmtStr {
+				t.Errorf("FormatMap() = %v, want %v", gotFmtStr, tt.wantFmtStr)
+			}
+		})
+	}
+}