add percent helper method to metrics

metrics/docker.go

@@ -86,7 +86,7 @@ func (c *Docker) ReadCPU(stats *api.Stats) {
 func (c *Docker) ReadMem(stats *api.Stats) {
 	c.MemUsage = int64(stats.MemoryStats.Usage)
 	c.MemLimit = int64(stats.MemoryStats.Limit)
-	c.MemPercent = round((float64(c.MemUsage) / float64(c.MemLimit)) * 100)
+	c.MemPercent = percent(float64(c.MemUsage), float64(c.MemLimit))
 }
 
 func (c *Docker) ReadNet(stats *api.Stats) {

metrics/main.go

@@ -43,3 +43,11 @@ type Collector interface {
 func round(num float64) int {
 	return int(num + math.Copysign(0.5, num))
 }
+
+// return rounded percentage
+func percent(val float64, total float64) int {
+	if total <= 0 {
+		return 0
+	}
+	return round((val / total) * 100)
+}

metrics/mock.go

@@ -60,7 +60,7 @@ func (c *Mock) run() {
 		if c.MemUsage > c.MemLimit {
 			c.MemUsage = 0
 		}
-		c.MemPercent = round((float64(c.MemUsage) / float64(c.MemLimit)) * 100)
+		c.MemPercent = percent(float64(c.MemUsage), float64(c.MemLimit))
 		c.stream <- c.Metrics
 		if c.done {
 			break

metrics/proc.go

@@ -19,6 +19,7 @@ func getSysMemTotal() int64 {
 	return int64(stat.MemTotal * 1024)
 }
 
+// return cumulative system cpu usage in nanoseconds
 func getSysCPUUsage() uint64 {
 	stat, err := linuxproc.ReadStat("/proc/stat")
 	if err != nil {

metrics/runc.go

@@ -95,7 +95,7 @@ func (c *Runc) ReadMem(stats *cgroups.Stats) {
 	if c.MemLimit > sysMemTotal && sysMemTotal > 0 {
 		c.MemLimit = sysMemTotal
 	}
-	c.MemPercent = round((float64(c.MemUsage) / float64(c.MemLimit)) * 100)
+	c.MemPercent = percent(float64(c.MemUsage), float64(c.MemLimit))
 }
 
 func (c *Runc) ReadNet(interfaces []*libcontainer.NetworkInterface) {