cmd/syncthing: Use a 10 second EWMA for CPU usage, refactor a little

We have it lying around so might as well use it instead of inventing our
own thing.

GitHub-Pull-Request: https://github.com/syncthing/syncthing/pull/4111

cmd/syncthing/cpuusage_solaris.go

@@ -59,40 +59,20 @@ type prusage_t struct {
 
 }
 
-func solarisPrusage(pid int, rusage *prusage_t) error {
-	fd, err := os.Open(fmt.Sprintf("/proc/%d/usage", pid))
+var procFile = fmt.Sprintf("/proc/%d/usage", os.Getpid())
+
+func cpuUsage() time.Duration {
+	fd, err := os.Open(procFile)
 	if err != nil {
-		return err
+		return 0
 	}
+
+	var rusage prusage_t
 	err = binary.Read(fd, binary.LittleEndian, rusage)
 	fd.Close()
-	return err
-}
-
-func init() {
-	go trackCPUUsage()
-}
-
-func trackCPUUsage() {
-	var prevUsage int64
-	var prevTime = time.Now().UnixNano()
-	var rusage prusage_t
-	var pid = os.Getpid()
-	for range time.NewTicker(time.Second).C {
-		err := solarisPrusage(pid, &rusage)
-		if err != nil {
-			l.Warnln("getting prusage:", err)
-			continue
-		}
-		curTime := time.Now().UnixNano()
-		timeDiff := curTime - prevTime
-		curUsage := rusage.Pr_utime.Nano() + rusage.Pr_stime.Nano()
-		usageDiff := curUsage - prevUsage
-		cpuUsageLock.Lock()
-		copy(cpuUsagePercent[1:], cpuUsagePercent[0:])
-		cpuUsagePercent[0] = 100 * float64(usageDiff) / float64(timeDiff)
-		cpuUsageLock.Unlock()
-		prevTime = curTime
-		prevUsage = curUsage
+	if err != nil {
+		return 0
 	}
+
+	return time.Duration(rusage.Pr_utime.Nano() + rusage.Pr_stime.Nano())
 }

cmd/syncthing/cpuusage_unix.go

@@ -0,0 +1,18 @@
+// Copyright (C) 2014 The Syncthing Authors.
+//
+// This Source Code Form is subject to the terms of the Mozilla Public
+// License, v. 2.0. If a copy of the MPL was not distributed with this file,
+// You can obtain one at https://mozilla.org/MPL/2.0/.
+
+//+build !windows,!solaris
+
+package main
+
+import "syscall"
+import "time"
+
+func cpuUsage() time.Duration {
+	var rusage syscall.Rusage
+	syscall.Getrusage(syscall.RUSAGE_SELF, &rusage)
+	return time.Duration(rusage.Utime.Nano() + rusage.Stime.Nano())
+}

cmd/syncthing/cpuusage_windows.go

@@ -0,0 +1,26 @@
+// Copyright (C) 2014 The Syncthing Authors.
+//
+// This Source Code Form is subject to the terms of the Mozilla Public
+// License, v. 2.0. If a copy of the MPL was not distributed with this file,
+// You can obtain one at https://mozilla.org/MPL/2.0/.
+
+//+build windows
+
+package main
+
+import "syscall"
+import "time"
+
+func cpuUsage() time.Duration {
+	handle, err := syscall.GetCurrentProcess()
+	if err != nil {
+		return 0
+	}
+
+	var ctime, etime, ktime, utime syscall.Filetime
+	if err := syscall.GetProcessTimes(handle, &ctime, &etime, &ktime, &utime); err != nil {
+		return 0
+	}
+
+	return time.Duration(ktime.Nanoseconds() + utime.Nanoseconds())
+}

cmd/syncthing/gui.go

@@ -11,6 +11,7 @@ import (
 	"encoding/json"
 	"fmt"
 	"io/ioutil"
+	"math"
 	"net"
 	"net/http"
 	"os"
@@ -846,8 +847,25 @@ func (s *apiService) flushResponse(resp string, w http.ResponseWriter) {
 	f.Flush()
 }
 
-var cpuUsagePercent [10]float64 // The last ten seconds
-var cpuUsageLock = sync.NewRWMutex()
+// 10 second average. Magic alpha value comes from looking at EWMA package
+// definitions of EWMA1, EWMA5.
+var cpuTickRate = 2 * time.Second
+var cpuAverage = metrics.NewEWMA(1 - math.Exp(-float64(cpuTickRate)/float64(time.Second)/10.0))
+
+func init() {
+	if !innerProcess {
+		return
+	}
+	go func() {
+		var prevUsage time.Duration
+		for range time.NewTicker(cpuTickRate).C {
+			curUsage := cpuUsage()
+			cpuAverage.Update(int64((curUsage - prevUsage) / time.Millisecond))
+			prevUsage = curUsage
+			cpuAverage.Tick()
+		}
+	}()
+}
 
 func (s *apiService) getSystemStatus(w http.ResponseWriter, r *http.Request) {
 	var m runtime.MemStats
@@ -875,14 +893,9 @@ func (s *apiService) getSystemStatus(w http.ResponseWriter, r *http.Request) {
 	}
 
 	res["connectionServiceStatus"] = s.connectionsService.Status()
-
-	cpuUsageLock.RLock()
-	var cpusum float64
-	for _, p := range cpuUsagePercent {
-		cpusum += p
-	}
-	cpuUsageLock.RUnlock()
-	res["cpuPercent"] = cpusum / float64(len(cpuUsagePercent)) / float64(runtime.NumCPU())
+	// cpuUsage.Rate() is in milliseconds per second, so dividing by ten
+	// gives us percent
+	res["cpuPercent"] = cpuAverage.Rate() / 10 / float64(runtime.NumCPU())
 	res["pathSeparator"] = string(filepath.Separator)
 	res["uptime"] = int(time.Since(startTime).Seconds())
 	res["startTime"] = startTime

cmd/syncthing/gui_unix.go

@@ -1,37 +0,0 @@
-// Copyright (C) 2014 The Syncthing Authors.
-//
-// This Source Code Form is subject to the terms of the Mozilla Public
-// License, v. 2.0. If a copy of the MPL was not distributed with this file,
-// You can obtain one at https://mozilla.org/MPL/2.0/.
-
-//+build !windows,!solaris
-
-package main
-
-import (
-	"syscall"
-	"time"
-)
-
-func init() {
-	go trackCPUUsage()
-}
-
-func trackCPUUsage() {
-	var prevUsage int64
-	var prevTime = time.Now().UnixNano()
-	var rusage syscall.Rusage
-	for range time.NewTicker(time.Second).C {
-		syscall.Getrusage(syscall.RUSAGE_SELF, &rusage)
-		curTime := time.Now().UnixNano()
-		timeDiff := curTime - prevTime
-		curUsage := rusage.Utime.Nano() + rusage.Stime.Nano()
-		usageDiff := curUsage - prevUsage
-		cpuUsageLock.Lock()
-		copy(cpuUsagePercent[1:], cpuUsagePercent[0:])
-		cpuUsagePercent[0] = 100 * float64(usageDiff) / float64(timeDiff)
-		cpuUsageLock.Unlock()
-		prevTime = curTime
-		prevUsage = curUsage
-	}
-}

cmd/syncthing/gui_windows.go

@@ -1,58 +0,0 @@
-// Copyright (C) 2014 The Syncthing Authors.
-//
-// This Source Code Form is subject to the terms of the Mozilla Public
-// License, v. 2.0. If a copy of the MPL was not distributed with this file,
-// You can obtain one at https://mozilla.org/MPL/2.0/.
-
-//+build windows
-
-package main
-
-import (
-	"syscall"
-	"time"
-)
-
-func init() {
-	go trackCPUUsage()
-}
-
-func trackCPUUsage() {
-	handle, err := syscall.GetCurrentProcess()
-	if err != nil {
-		l.Warnln("Cannot track CPU usage:", err)
-		return
-	}
-
-	var ctime, etime, ktime, utime syscall.Filetime
-	err = syscall.GetProcessTimes(handle, &ctime, &etime, &ktime, &utime)
-	if err != nil {
-		l.Warnln("Cannot track CPU usage:", err)
-		return
-	}
-
-	prevTime := ctime.Nanoseconds()
-	prevUsage := ktime.Nanoseconds() + utime.Nanoseconds() // Always overflows
-
-	for range time.NewTicker(time.Second).C {
-		err := syscall.GetProcessTimes(handle, &ctime, &etime, &ktime, &utime)
-		if err != nil {
-			continue
-		}
-
-		curTime := time.Now().UnixNano()
-		timeDiff := curTime - prevTime
-		// This is sometimes 0, no clue why.
-		if timeDiff == 0 {
-			continue
-		}
-		curUsage := ktime.Nanoseconds() + utime.Nanoseconds()
-		usageDiff := curUsage - prevUsage
-		cpuUsageLock.Lock()
-		copy(cpuUsagePercent[1:], cpuUsagePercent[0:])
-		cpuUsagePercent[0] = 100 * float64(usageDiff) / float64(timeDiff)
-		cpuUsageLock.Unlock()
-		prevTime = curTime
-		prevUsage = curUsage
-	}
-}