runtime: additional map benchmarks for repeated lookups

For the future.

Update #5147

R=khr, r
CC=golang-dev
https://golang.org/cl/8165044

diff --git a/src/pkg/runtime/mapspeed_test.go b/src/pkg/runtime/mapspeed_test.go
index a3797406064188025ed8a7d281181cf766daae52..4d77347b24433a73092a5bc7f7878d2f8a36ec88 100644 (file)
--- a/src/pkg/runtime/mapspeed_test.go
+++ b/src/pkg/runtime/mapspeed_test.go
@@ -138,6 +138,7 @@ func BenchmarkSmallStrMap(b *testing.B) {
                _, _ = m[key]
        }
 }
+
 func BenchmarkIntMap(b *testing.B) {
        m := make(map[int]bool)
        for i := 0; i < 8; i++ {
@@ -148,3 +149,25 @@ func BenchmarkIntMap(b *testing.B) {
                _, _ = 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) }