keepalive_time_when
val = keepalive_time_when(tp) / HZ;
tcp_reset_keepalive_timer(sk, keepalive_time_when(tp));
tcp_reset_keepalive_timer(newsk, keepalive_time_when(newtp));
tcp_reset_keepalive_timer(sk, keepalive_time_when(tcp_sk(sk)));
elapsed = keepalive_time_when(tp);
if (elapsed >= keepalive_time_when(tp)) {
elapsed = keepalive_time_when(tp) - elapsed;