def update(self) -> None:
        """
        Update the elapsed time.

        For more info on how to set the initial time see the class description.

        :return: None.
        """
        now = time.perf_counter()
        if self._init_time is None:
            self._init_time = now
        self._prev_time = now

        Update the elapsed time.

        For more info on how to set the initial time see the class description.

        :return: None.
        
avalanche/evaluation/metrics/timing.py