Print the single thread hash performance at startup

cmd/syncthing/main.go

@@ -516,6 +516,7 @@ func syncthingMain() {
 
 	l.Infoln(LongVersion)
 	l.Infoln("My ID:", myID)
+	printHashRate()
 
 	// Emit the Starting event, now that we know who we are.
 
@@ -836,6 +837,22 @@ func syncthingMain() {
 	os.Exit(code)
 }
 
+// printHashRate prints the hashing performance in MB/s, formatting it with
+// appropriate precision for the value, i.e. 182 MB/s, 18 MB/s, 1.8 MB/s, 0.18
+// MB/s.
+func printHashRate() {
+	hashRate := cpuBench(3, 100*time.Millisecond)
+
+	decimals := 0
+	if hashRate < 1 {
+		decimals = 2
+	} else if hashRate < 10 {
+		decimals = 1
+	}
+
+	l.Infof("Single thread hash performance is ~%.*f MB/s", decimals, hashRate)
+}
+
 func loadConfig(cfgFile string) (*config.Wrapper, string, error) {
 	info, err := os.Stat(cfgFile)
 	if err != nil {

cmd/syncthing/usage_report.go

@@ -112,15 +112,7 @@ func reportData(cfg *config.Wrapper, m *model.Model) map[string]interface{} {
 	var mem runtime.MemStats
 	runtime.ReadMemStats(&mem)
 	res["memoryUsageMiB"] = (mem.Sys - mem.HeapReleased) / 1024 / 1024
-
-	var perf float64
-	for i := 0; i < 5; i++ {
-		p := cpuBench()
-		if p > perf {
-			perf = p
-		}
-	}
-	res["sha256Perf"] = perf
+	res["sha256Perf"] = cpuBench(5, 125*time.Millisecond)
 
 	bytes, err := memorySize()
 	if err == nil {
@@ -301,7 +293,17 @@ func (s *usageReportingService) Stop() {
 }
 
 // cpuBench returns CPU performance as a measure of single threaded SHA-256 MiB/s
-func cpuBench() float64 {
+func cpuBench(iterations int, duration time.Duration) float64 {
+	var perf float64
+	for i := 0; i < iterations; i++ {
+		if v := cpuBenchOnce(duration); v > perf {
+			perf = v
+		}
+	}
+	return perf
+}
+
+func cpuBenchOnce(duration time.Duration) float64 {
 	chunkSize := 100 * 1 << 10
 	h := sha256.New()
 	bs := make([]byte, chunkSize)
@@ -309,7 +311,7 @@ func cpuBench() float64 {
 
 	t0 := time.Now()
 	b := 0
-	for time.Since(t0) < 125*time.Millisecond {
+	for time.Since(t0) < duration {
 		h.Write(bs)
 		b += chunkSize
 	}