NS_PER_SEC
div_u64_rem(ns, NS_PER_SEC, &rem);
rem = (NS_PER_SEC - rem);
div_u64_rem(ns, NS_PER_SEC, &rem);
rem = (NS_PER_SEC - rem);
dt /= NS_PER_SEC;
uint64_t delay_ns = ((uint64_t)skb->len) * NS_PER_SEC / target_rate;
start_ns = t_start.tv_sec * NS_PER_SEC + t_start.tv_nsec;
end_ns = t_end.tv_sec * NS_PER_SEC + t_end.tv_nsec;