taglinefilesource code
ssthresh144include/net/sock.hvolatile unsigned short  ssthresh;
ssthresh660net/ipv4/af_inet.csk->ssthresh = 0;
ssthresh844net/ipv4/tcp.csk->ssthresh = sk->cong_window >> 1; /* remember window where we lost */
ssthresh2959net/ipv4/tcp.cnewsk->ssthresh = 0;
ssthresh3502net/ipv4/tcp.cif (sk->cong_window < sk->ssthresh)