Function readSystemCPUUsage

pkg/cmd/container/stats_linux.go:150–188

readSystemCPUUsage parses CPU usage information from a reader providing proc/stat format data. It returns the total CPU usage in nanoseconds and the number of CPUs. More: https://github.com/moby/moby/blob/26db31fdab628a2345ed8f179e575099384166a9/daemon/stats_unix.go#L327-L368

(r io.Reader)

// and the number of CPUs. More:
// https://github.com/moby/moby/blob/26db31fdab628a2345ed8f179e575099384166a9/daemon/stats_unix.go#L327-L368
func readSystemCPUUsage(r io.Reader) (cpuUsage uint64, cpuNum uint32, _ error) {
	rdr := bufio.NewReaderSize(r, 1024)

	for {
		data, isPartial, err := rdr.ReadLine()

		if err != nil {
			return 0, 0, fmt.Errorf("error scanning /proc/stat file: %w", err)
		}
		// Assume all cpu* records are at the start of the file, like glibc:
		// https://github.com/bminor/glibc/blob/5d00c201b9a2da768a79ea8d5311f257871c0b43/sysdeps/unix/sysv/linux/getsysstats.c#L108-L135
		if isPartial || len(data) < 4 {
			break
		}
		line := string(data)
		if line[:3] != "cpu" {
			break
		}
		if line[3] == ' ' {
			parts := strings.Fields(line)
			if len(parts) < 8 {
				return 0, 0, fmt.Errorf("invalid number of cpu fields")
			}
			var totalClockTicks uint64
			for _, i := range parts[1:8] {
				v, err := strconv.ParseUint(i, 10, 64)
				if err != nil {
					return 0, 0, fmt.Errorf("unable to convert value %s to int: %w", i, err)
				}
				totalClockTicks += v
			}
			cpuUsage = (totalClockTicks * nanoSecondsPerSecond) / clockTicksPerSecond
		}
		if '0' <= line[3] && line[3] <= '9' {
			cpuNum++
		}
	}
	return cpuUsage, cpuNum, nil
}