Fix docker memory and cpu reporting in Windows (#3043)

plugins/inputs/docker/stats_helpers.go

@@ -0,0 +1,55 @@
+// Helper functions copied from
+// https://github.com/docker/cli/blob/master/cli/command/container/stats_helpers.go
+package docker
+
+import "github.com/docker/docker/api/types"
+
+func calculateCPUPercentUnix(previousCPU, previousSystem uint64, v *types.StatsJSON) float64 {
+	var (
+		cpuPercent = 0.0
+		// calculate the change for the cpu usage of the container in between readings
+		cpuDelta = float64(v.CPUStats.CPUUsage.TotalUsage) - float64(previousCPU)
+		// calculate the change for the entire system between readings
+		systemDelta = float64(v.CPUStats.SystemUsage) - float64(previousSystem)
+		onlineCPUs  = float64(v.CPUStats.OnlineCPUs)
+	)
+
+	if onlineCPUs == 0.0 {
+		onlineCPUs = float64(len(v.CPUStats.CPUUsage.PercpuUsage))
+	}
+	if systemDelta > 0.0 && cpuDelta > 0.0 {
+		cpuPercent = (cpuDelta / systemDelta) * onlineCPUs * 100.0
+	}
+	return cpuPercent
+}
+
+func calculateCPUPercentWindows(v *types.StatsJSON) float64 {
+	// Max number of 100ns intervals between the previous time read and now
+	possIntervals := uint64(v.Read.Sub(v.PreRead).Nanoseconds()) // Start with number of ns intervals
+	possIntervals /= 100                                         // Convert to number of 100ns intervals
+	possIntervals *= uint64(v.NumProcs)                          // Multiple by the number of processors
+
+	// Intervals used
+	intervalsUsed := v.CPUStats.CPUUsage.TotalUsage - v.PreCPUStats.CPUUsage.TotalUsage
+
+	// Percentage avoiding divide-by-zero
+	if possIntervals > 0 {
+		return float64(intervalsUsed) / float64(possIntervals) * 100.0
+	}
+	return 0.00
+}
+
+// calculateMemUsageUnixNoCache calculate memory usage of the container.
+// Page cache is intentionally excluded to avoid misinterpretation of the output.
+func calculateMemUsageUnixNoCache(mem types.MemoryStats) float64 {
+	return float64(mem.Usage - mem.Stats["cache"])
+}
+
+func calculateMemPercentUnixNoCache(limit float64, usedNoCache float64) float64 {
+	// MemoryStats.Limit will never be 0 unless the container is not running and we haven't
+	// got any data from cgroup
+	if limit != 0 {
+		return usedNoCache / limit * 100.0
+	}
+	return 0
+}