@staticmethod
def percent_cpu_usage(previous, current):
    """Return the percentage cpu time used since previous update.

        :param syskit.Process previous: The Process object from last update.
        :param syskit.Process current: The current Process object.
        """
    last_cpu_time = float(previous.cputime)
    last_clock_time = float(previous.refreshed.timestamp())
    cpu_time = float(current.cputime)
    clock_time = current.refreshed.timestamp()
    cpu_time_passed = cpu_time - last_cpu_time
    clock_time_passed = clock_time - last_clock_time
    if clock_time_passed == 0:
        return 0
    percent_cpu_usage = cpu_time_passed / clock_time_passed * 100
    return percent_cpu_usage
