[dev.fuzz] internal/fuzz: stablize mutator benchmark and add additional benchmarks

Adds a few new benchmarks, and attempts to reduce the variability of the
existing BenchmarkMutatorBytes benchmark. These should help provide some
insight when we're working on performance issues.

Change-Id: I45b68ae36da99ec2eb4a610b7a3fc6fbf3d9494a
Reviewed-on: https://go-review.googlesource.com/c/go/+/324969
Trust: Roland Shoemaker <roland@golang.org>
Trust: Katie Hockman <katie@golang.org>
Run-TryBot: Roland Shoemaker <roland@golang.org>
Reviewed-by: Katie Hockman <katie@golang.org>
TryBot-Result: Go Bot <gobot@golang.org>

src/internal/fuzz/mutator_test.go

@@ -5,11 +5,17 @@
 package fuzz
 
 import (
+	"fmt"
+	"os"
 	"strconv"
 	"testing"
 )
 
 func BenchmarkMutatorBytes(b *testing.B) {
+	origEnv := os.Getenv("GODEBUG")
+	defer func() { os.Setenv("GODEBUG", origEnv) }()
+	os.Setenv("GODEBUG", fmt.Sprintf("%s,fuzzseed=123", origEnv))
+
 	for _, size := range []int{
 		1,
 		10,
@@ -20,10 +26,74 @@ func BenchmarkMutatorBytes(b *testing.B) {
 	} {
 		size := size
 		b.Run(strconv.Itoa(size), func(b *testing.B) {
-			vals := []interface{}{make([]byte, size)}
-			m := newMutator()
+			buf := make([]byte, size)
+			b.ResetTimer()
+
 			for i := 0; i < b.N; i++ {
-				m.mutate(vals, workerSharedMemSize)
+				// resize buffer to the correct shape and reset the PCG
+				buf = buf[0:size]
+				m := newMutator()
+				m.mutate([]interface{}{buf}, workerSharedMemSize)
+			}
+		})
+	}
+}
+
+func BenchmarkMutatorString(b *testing.B) {
+	origEnv := os.Getenv("GODEBUG")
+	defer func() { os.Setenv("GODEBUG", origEnv) }()
+	os.Setenv("GODEBUG", fmt.Sprintf("%s,fuzzseed=123", origEnv))
+
+	for _, size := range []int{
+		1,
+		10,
+		100,
+		1000,
+		10000,
+		100000,
+	} {
+		size := size
+		b.Run(strconv.Itoa(size), func(b *testing.B) {
+			buf := make([]byte, size)
+			b.ResetTimer()
+
+			for i := 0; i < b.N; i++ {
+				// resize buffer to the correct shape and reset the PCG
+				buf = buf[0:size]
+				m := newMutator()
+				m.mutate([]interface{}{string(buf)}, workerSharedMemSize)
+			}
+		})
+	}
+}
+
+func BenchmarkMutatorAllBasicTypes(b *testing.B) {
+	origEnv := os.Getenv("GODEBUG")
+	defer func() { os.Setenv("GODEBUG", origEnv) }()
+	os.Setenv("GODEBUG", fmt.Sprintf("%s,fuzzseed=123", origEnv))
+
+	types := []interface{}{
+		[]byte(""),
+		string(""),
+		false,
+		float32(0),
+		float64(0),
+		int(0),
+		int8(0),
+		int16(0),
+		int32(0),
+		int64(0),
+		uint8(0),
+		uint16(0),
+		uint32(0),
+		uint64(0),
+	}
+
+	for _, t := range types {
+		b.Run(fmt.Sprintf("%T", t), func(b *testing.B) {
+			for i := 0; i < b.N; i++ {
+				m := newMutator()
+				m.mutate([]interface{}{t}, workerSharedMemSize)
 			}
 		})
 	}

src/internal/fuzz/worker_test.go

@@ -0,0 +1,42 @@
+// Copyright 2021 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 fuzz
+
+import (
+	"context"
+	"fmt"
+	"os"
+	"testing"
+)
+
+func BenchmarkWorkerFuzzOverhead(b *testing.B) {
+	origEnv := os.Getenv("GODEBUG")
+	defer func() { os.Setenv("GODEBUG", origEnv) }()
+	os.Setenv("GODEBUG", fmt.Sprintf("%s,fuzzseed=123", origEnv))
+
+	ws := &workerServer{
+		fuzzFn:     func(_ CorpusEntry) error { return nil },
+		workerComm: workerComm{memMu: make(chan *sharedMem, 1)},
+	}
+
+	mem, err := sharedMemTempFile(workerSharedMemSize)
+	if err != nil {
+		b.Fatalf("failed to create temporary shared memory file: %s", err)
+	}
+
+	initialVal := []interface{}{make([]byte, 32)}
+	encodedVals := marshalCorpusFile(initialVal...)
+	mem.setValue(encodedVals)
+
+	ws.memMu <- mem
+
+	b.ResetTimer()
+	for i := 0; i < b.N; i++ {
+		ws.m = newMutator()
+		mem.setValue(encodedVals)
+
+		ws.fuzz(context.Background(), fuzzArgs{Limit: 1})
+	}
+}