'Calculate a delta value from two performance counters.'

def _get_performance_counter_delta(self, counters_t1, counters_t2, counter_name):

    counter_t1 = int(self._find_performance_counter_value(counters_t1, counter_name))
    counter_t2 = int(self._find_performance_counter_value(counters_t2, counter_name))
    return (counter_t2 - counter_t1)
