cpustatMetric.go: Use derived values instead of absolute values

The values in /proc/stat are absolute counters related to the boot
  time of the system. To obtain a utilization of the CPU, the changes
  in the counters must be derived according to time. To take only the
  absolute values leads to the fact that changes in the utilization,
  straight with larger values, do not become visible.

collectors/cpustatMetric.go

@@ -11,6 +11,7 @@ import (
 
 	cclog "github.com/ClusterCockpit/cc-metric-collector/internal/ccLogger"
 	lp "github.com/ClusterCockpit/cc-metric-collector/internal/ccMetric"
+	sysconf "github.com/tklauser/go-sysconf"
 )
 
 const CPUSTATFILE = `/proc/stat`
@@ -22,9 +23,11 @@ type CpustatCollectorConfig struct {
 type CpustatCollector struct {
 	metricCollector
 	config   CpustatCollectorConfig
+	lastTimestamp time.Time                   // Store time stamp of last tick to derive values
 	matches  map[string]int
 	cputags  map[string]map[string]string
 	nodetags map[string]string
+	olddata  map[string]map[string]int64
 }
 
 func (m *CpustatCollector) Init(config json.RawMessage) error {
@@ -76,36 +79,48 @@ func (m *CpustatCollector) Init(config json.RawMessage) error {
 	// Pre-generate tags for all CPUs
 	num_cpus := 0
 	m.cputags = make(map[string]map[string]string)
+	m.olddata = make(map[string]map[string]int64)
 	scanner := bufio.NewScanner(file)
 	for scanner.Scan() {
 		line := scanner.Text()
 		linefields := strings.Fields(line)
-		if strings.HasPrefix(linefields[0], "cpu") && strings.Compare(linefields[0], "cpu") != 0 {
+		if strings.Compare(linefields[0], "cpu") == 0 {
+			m.olddata["cpu"] = make(map[string]int64)
+			for k, v := range m.matches {
+				m.olddata["cpu"][k], _ = strconv.ParseInt(linefields[v], 0, 64)
+			}
+		} else if strings.HasPrefix(linefields[0], "cpu") && strings.Compare(linefields[0], "cpu") != 0 {
 			cpustr := strings.TrimLeft(linefields[0], "cpu")
 			cpu, _ := strconv.Atoi(cpustr)
 			m.cputags[linefields[0]] = map[string]string{"type": "hwthread", "type-id": fmt.Sprintf("%d", cpu)}
+			m.olddata[linefields[0]] = make(map[string]int64)
+			for k, v := range m.matches {
+				m.olddata[linefields[0]][k], _ = strconv.ParseInt(linefields[v], 0, 64)
+			}
 			num_cpus++
 		}
 	}
+	m.lastTimestamp = time.Now()
 	m.init = true
 	return nil
 }
 
-func (m *CpustatCollector) parseStatLine(linefields []string, tags map[string]string, output chan lp.CCMetric) {
+func (m *CpustatCollector) parseStatLine(linefields []string, tags map[string]string, output chan lp.CCMetric, now time.Time, tsdelta time.Duration) {
 	values := make(map[string]float64)
-	total := 0.0
+	clktck, _ := sysconf.Sysconf(sysconf.SC_CLK_TCK)
 	for match, index := range m.matches {
 		if len(match) > 0 {
 			x, err := strconv.ParseInt(linefields[index], 0, 64)
 			if err == nil {
-				values[match] = float64(x)
+				vdiff := x - m.olddata[linefields[0]][match]
-				total += values[match]
+				m.olddata[linefields[0]][match] = x // Store new value for next run
+				values[match] = float64(vdiff) / float64(tsdelta.Seconds()) / float64(clktck)
 			}
 		}
 	}
-	t := time.Now()
+	
 	for name, value := range values {
-		y, err := lp.New(name, tags, m.meta, map[string]interface{}{"value": (value * 100.0) / total}, t)
+		y, err := lp.New(name, tags, m.meta, map[string]interface{}{"value": value * 100}, now)
 		if err == nil {
 			output <- y
 		}
@@ -117,6 +132,9 @@ func (m *CpustatCollector) Read(interval time.Duration, output chan lp.CCMetric)
 		return
 	}
 	num_cpus := 0
+	now := time.Now()
+	tsdelta := now.Sub(m.lastTimestamp)
+
 	file, err := os.Open(string(CPUSTATFILE))
 	if err != nil {
 		cclog.ComponentError(m.name, err.Error())
@@ -128,9 +146,9 @@ func (m *CpustatCollector) Read(interval time.Duration, output chan lp.CCMetric)
 		line := scanner.Text()
 		linefields := strings.Fields(line)
 		if strings.Compare(linefields[0], "cpu") == 0 {
-			m.parseStatLine(linefields, m.nodetags, output)
+			m.parseStatLine(linefields, m.nodetags, output, now, tsdelta)
 		} else if strings.HasPrefix(linefields[0], "cpu") {
-			m.parseStatLine(linefields, m.cputags[linefields[0]], output)
+			m.parseStatLine(linefields, m.cputags[linefields[0]], output, now, tsdelta)
 			num_cpus++
 		}
 	}
@@ -139,11 +157,13 @@ func (m *CpustatCollector) Read(interval time.Duration, output chan lp.CCMetric)
 		m.nodetags,
 		m.meta,
 		map[string]interface{}{"value": int(num_cpus)},
-		time.Now(),
+		now,
 	)
 	if err == nil {
 		output <- num_cpus_metric
 	}
+
+	m.lastTimestamp = now
 }
 
 func (m *CpustatCollector) Close() {