func InstCpuStats()

in info/v2/conversion.go [232:282]
48 lines of code
10 McCabe index (conditional complexity)

func InstCpuStats(last, cur *v1.ContainerStats) (*CpuInstStats, error) {
	if last == nil {
		return nil, nil
	}
	if !cur.Timestamp.After(last.Timestamp) {
		return nil, fmt.Errorf("container stats move backwards in time")
	}
	if len(last.Cpu.Usage.PerCpu) != len(cur.Cpu.Usage.PerCpu) {
		return nil, fmt.Errorf("different number of cpus")
	}
	timeDelta := cur.Timestamp.Sub(last.Timestamp)
	// Nanoseconds to gain precision and avoid having zero seconds if the
	// difference between the timestamps is just under a second
	timeDeltaNs := uint64(timeDelta.Nanoseconds())
	convertToRate := func(lastValue, curValue uint64) (uint64, error) {
		if curValue < lastValue {
			return 0, fmt.Errorf("cumulative stats decrease")
		}
		valueDelta := curValue - lastValue
		// Use float64 to keep precision
		return uint64(float64(valueDelta) / float64(timeDeltaNs) * 1e9), nil
	}
	total, err := convertToRate(last.Cpu.Usage.Total, cur.Cpu.Usage.Total)
	if err != nil {
		return nil, err
	}
	percpu := make([]uint64, len(last.Cpu.Usage.PerCpu))
	for i := range percpu {
		var err error
		percpu[i], err = convertToRate(last.Cpu.Usage.PerCpu[i], cur.Cpu.Usage.PerCpu[i])
		if err != nil {
			return nil, err
		}
	}
	user, err := convertToRate(last.Cpu.Usage.User, cur.Cpu.Usage.User)
	if err != nil {
		return nil, err
	}
	system, err := convertToRate(last.Cpu.Usage.System, cur.Cpu.Usage.System)
	if err != nil {
		return nil, err
	}
	return &CpuInstStats{
		Usage: CpuInstUsage{
			Total:  total,
			PerCpu: percpu,
			User:   user,
			System: system,
		},
	}, nil
}