taglinefilesource code
ssthresh162include/net/sock.hvolatile unsigned short  ssthresh;
ssthresh846net/ipv4/tcp.csk->ssthresh = sk->cong_window >> 1; /* remember window where we lost */
ssthresh2949net/ipv4/tcp.cnewsk->ssthresh = 0;
ssthresh3493net/ipv4/tcp.cif (sk->cong_window < sk->ssthresh)