def total_items_per_ms(self):
        if self.total_item_count == 0:
            return None
        else:
            return float(self.total_item_count) / float(self.total_duration_ms)
Returns the speed of travelling wave.
dataset/ETHPy150Open matrix-org/synapse/synapse/storage/background_updates.py/BackgroundUpdatePerformance.total_items_per_ms--crossover with--dataset/ETHPy150Open sympy/sympy/sympy/physics/optics/waves.py/TWave.speed