code review 8165044: runtime: some addition map benchmarks

src/pkg/runtime/mapspeed_test.go

 // Copyright 2013 The Go Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 package runtime_test
 
 import (
         "fmt"
         "strings"
         "testing"
 )
@@ skipping 120 matching lines @@
         m := make(map[string]bool)
         for suffix := 'A'; suffix <= 'G'; suffix++ {
                 m[fmt.Sprint(suffix)] = true
         }
         key := "k"
         b.ResetTimer()
         for i := 0; i < b.N; i++ {
                 _, _ = m[key]
         }
 }
+
 func BenchmarkIntMap(b *testing.B) {
         m := make(map[int]bool)
         for i := 0; i < 8; i++ {
                 m[i] = true
         }
         b.ResetTimer()
         for i := 0; i < b.N; i++ {
                 _, _ = m[7]
         }
 }
+
+// Accessing the same keys in a row.
+func benchmarkRepeatedLookup(b *testing.B, lookupKeySize int) {
+        m := make(map[string]bool)
+        // At least bigger than a single bucket:
+        for i := 0; i < 64; i++ {
+                m[fmt.Sprintf("some key %d", i)] = true
+        }
+        base := strings.Repeat("x", lookupKeySize-1)
+        key1 := base + "1"
+        key2 := base + "2"
+        b.ResetTimer()
+        for i := 0; i < b.N/4; i++ {
+                _ = m[key1]
+                _ = m[key1]
+                _ = m[key2]
+                _ = m[key2]
+        }
+}
+
+func BenchmarkRepeatedLookupStrMapKey32(b *testing.B) { benchmarkRepeatedLookup(b, 32) }
+func BenchmarkRepeatedLookupStrMapKey1M(b *testing.B) { benchmarkRepeatedLookup(b, 1<<20) }