13+

test/bench/perf/bench1.go

+package main
+
+import (
+	"time"
+)
+
+func Benchmark(N int64) error {
+	// 13+
+	time.Sleep(time.Duration(N) * time.Millisecond)
+	return nil
+}

test/bench/perf/bench2.go

+package main
+
+func Benchmark(N int64) error {
+	return nil
+}

test/bench/perf/driver.go

+package main
+
+import (
+	"flag"
+	"fmt"
+	"os"
+	"time"
+)
+
+var (
+	benchNum  = flag.Int("benchnum", 3, "run each benchmark that many times")
+	benchTime = flag.Duration("benchtime", 10*time.Second, "benchmarking time for a single run")
+	benchMem  = flag.Int("benchmem", 64, "approx RSS value to aim at in benchmarks, in MB")
+)
+
+type Result struct {
+	N       int64
+	RunTime time.Duration
+}
+
+func main() {
+	flag.Parse()
+	var res Result
+	for i := 0; i < *benchNum; i++ {
+		res1 := RunBenchmark()
+		if res.RunTime == 0 || res.RunTime > res1.RunTime {
+			res = res1
+		}
+	}
+	fmt.Printf("GOPERF-METRIC:runtime=%v\n", int64(res.RunTime)/res.N)
+}
+
+func RunBenchmark() Result {
+	var res Result
+	for ChooseN(&res) {
+		res = RunOnce(res.N)
+	}
+	return res
+}
+
+func RunOnce(N int64) Result {
+	fmt.Printf("Benchmarking %v iterations\n", N)
+	t0 := time.Now()
+	err := Benchmark(N)
+	if err != nil {
+		fmt.Printf("Benchmark function failed: %v\n", err)
+		os.Exit(1)
+	}
+	res := Result{N: N}
+	res.RunTime = time.Since(t0)
+	return res
+}
+
+func ChooseN(res *Result) bool {
+	const MaxN = 1e12
+	last := res.N
+	if last == 0 {
+		res.N = 1
+		return true
+	} else if res.RunTime >= *benchTime || last >= MaxN {
+		return false
+	}
+	nsPerOp := max(1, int64(res.RunTime)/last)
+	res.N = int64(*benchTime) / nsPerOp
+	res.N = max(min(res.N+res.N/2, 100*last), last+1)
+	res.N = roundUp(res.N)
+	return true
+}
+
+func roundUp(n int64) int64 {
+	tmp := n
+	base := int64(1)
+	for tmp >= 10 {
+		tmp /= 10
+		base *= 10
+	}
+	switch {
+	case n <= base:
+		return base
+	case n <= (2 * base):
+		return 2 * base
+	case n <= (5 * base):
+		return 5 * base
+	default:
+		return 10 * base
+	}
+	panic("unreachable")
+	return 0
+}
+
+func min(a, b int64) int64 {
+	if a < b {
+		return a
+	}
+	return b
+}
+
+func max(a, b int64) int64 {
+	if a > b {
+		return a
+	}
+	return b
+}