runtime/pprof: add label benchmark

Add several benchmarks for pprof labels to analyze the impact of
follow-up CLs.

Change-Id: Ifae39cfe83ec93858fce9e3af6c1be024ba76736
Reviewed-on: https://go-review.googlesource.com/c/go/+/574515
Auto-Submit: Ian Lance Taylor <iant@golang.org>
Reviewed-by: David Chase <drchase@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: Michael Pratt <mpratt@google.com>

src/runtime/pprof/label_test.go

@@ -6,6 +6,7 @@ package pprof
 
 import (
 	"context"
+	"fmt"
 	"reflect"
 	"slices"
 	"strings"
@@ -111,3 +112,75 @@ func TestLabelMapStringer(t *testing.T) {
 		}
 	}
 }
+
+func BenchmarkLabels(b *testing.B) {
+	b.Run("set-one", func(b *testing.B) {
+		b.ReportAllocs()
+		b.ResetTimer()
+		for i := 0; i < b.N; i++ {
+			Do(context.Background(), Labels("key", "value"), func(context.Context) {})
+		}
+	})
+
+	b.Run("merge-one", func(b *testing.B) {
+		ctx := WithLabels(context.Background(), Labels("key1", "val1"))
+
+		b.ReportAllocs()
+		b.ResetTimer()
+		for i := 0; i < b.N; i++ {
+			Do(ctx, Labels("key2", "value2"), func(context.Context) {})
+		}
+	})
+
+	b.Run("overwrite-one", func(b *testing.B) {
+		ctx := WithLabels(context.Background(), Labels("key", "val"))
+
+		b.ReportAllocs()
+		b.ResetTimer()
+		for i := 0; i < b.N; i++ {
+			Do(ctx, Labels("key", "value"), func(context.Context) {})
+		}
+	})
+
+	for _, scenario := range []string{"ordered", "unordered"} {
+		var labels []string
+		for i := 0; i < 10; i++ {
+			labels = append(labels, fmt.Sprintf("key%03d", i), fmt.Sprintf("value%03d", i))
+		}
+		if scenario == "unordered" {
+			labels[0], labels[len(labels)-1] = labels[len(labels)-1], labels[0]
+		}
+
+		b.Run(scenario, func(b *testing.B) {
+			b.Run("set-many", func(b *testing.B) {
+				b.ReportAllocs()
+				b.ResetTimer()
+				for i := 0; i < b.N; i++ {
+					Do(context.Background(), Labels(labels...), func(context.Context) {})
+				}
+			})
+
+			b.Run("merge-many", func(b *testing.B) {
+				ctx := WithLabels(context.Background(), Labels(labels[:len(labels)/2]...))
+
+				b.ResetTimer()
+				b.ReportAllocs()
+				for i := 0; i < b.N; i++ {
+					Do(ctx, Labels(labels[len(labels)/2:]...), func(context.Context) {})
+				}
+			})
+
+			b.Run("overwrite-many", func(b *testing.B) {
+				ctx := WithLabels(context.Background(), Labels(labels...))
+
+				b.ReportAllocs()
+				b.ResetTimer()
+				for i := 0; i < b.N; i++ {
+					Do(ctx, Labels(labels...), func(context.Context) {})
+				}
+			})
+		})
+	}
+
+	// TODO: hit slow path in Labels
+}