Add performance stats collection

.gitignore

@@ -8,3 +8,6 @@ discosrv
 .jshintrc
 coverage.out
 files/pidx
+discosrv.exe
+bin
+perfstats*.csv

cmd/syncthing/perfstats.go

@@ -0,0 +1,45 @@
+// +build perfstats
+
+package main
+
+import (
+	"fmt"
+	"os"
+	"runtime"
+	"syscall"
+	"time"
+)
+
+func init() {
+	go savePerfStats(fmt.Sprintf("perfstats-%d.csv", syscall.Getpid()))
+}
+
+func savePerfStats(file string) {
+	fd, err := os.Create(file)
+	if err != nil {
+		panic(err)
+	}
+
+	var prevUsage int64
+	var prevTime int64
+	var rusage syscall.Rusage
+	var memstats runtime.MemStats
+
+	t0 := time.Now()
+	for t := range time.NewTicker(250 * time.Millisecond).C {
+		syscall.Getrusage(syscall.RUSAGE_SELF, &rusage)
+		curTime := time.Now().UnixNano()
+		timeDiff := curTime - prevTime
+		curUsage := rusage.Utime.Nano() + rusage.Stime.Nano()
+		usageDiff := curUsage - prevUsage
+		cpuUsagePercent := 100 * float64(usageDiff) / float64(timeDiff)
+		prevTime = curTime
+		prevUsage = curUsage
+
+		runtime.ReadMemStats(&memstats)
+
+		startms := int(t.Sub(t0).Seconds() * 1000)
+
+		fmt.Fprintf(fd, "%d\t%f\t%d\t%d\n", startms, cpuUsagePercent, memstats.Alloc, memstats.Sys)
+	}
+}