struct timeval current_time;
struct timeval last_time;
unsigned long distance_time = 0;
do_gettimeofday(&last_time);
//do something
do_gettimeofday(¤t_time);
distance_time = (current_time.tv_sec - last_time.tv_sec) * 1000000 +
(current_time.tv_usec - last_time.tv_usec);