Function tcp_prr_partialack

freebsd/netinet/tcp_input.c:3921–3972

}

void
tcp_prr_partialack(struct tcpcb *tp, struct tcphdr *th)
{
	int snd_cnt = 0, limit = 0, del_data = 0, pipe = 0;
	int maxseg = tcp_maxseg(tp);

	INP_WLOCK_ASSERT(tp->t_inpcb);

	tcp_timer_activate(tp, TT_REXMT, 0);
	tp->t_rtttime = 0;
	/*
	 * Compute the amount of data that this ACK is indicating
	 * (del_data) and an estimate of how many bytes are in the
	 * network.
	 */
	del_data = tp->sackhint.delivered_data;
	if (V_tcp_do_rfc6675_pipe)
		pipe = tcp_compute_pipe(tp);
	else
		pipe = (tp->snd_nxt - tp->snd_fack) + tp->sackhint.sack_bytes_rexmit;
	tp->sackhint.prr_delivered += del_data;
	/*
	 * Proportional Rate Reduction
	 */
	if (pipe >= tp->snd_ssthresh) {
		if (tp->sackhint.recover_fs == 0)
			tp->sackhint.recover_fs =
			    imax(1, tp->snd_nxt - tp->snd_una);
		snd_cnt = howmany((long)tp->sackhint.prr_delivered *
			    tp->snd_ssthresh, tp->sackhint.recover_fs) -
			    tp->sackhint.prr_out;
	} else {
		if (V_tcp_do_prr_conservative)
			limit = tp->sackhint.prr_delivered -
			    tp->sackhint.prr_out;
		else
			limit = imax(tp->sackhint.prr_delivered -
				    tp->sackhint.prr_out, del_data) +
				    maxseg;
		snd_cnt = imin((tp->snd_ssthresh - pipe), limit);
	}
	snd_cnt = imax(snd_cnt, 0) / maxseg;
	/*
	 * Send snd_cnt new data into the network in response to this ack.
	 * If there is going to be a SACK retransmission, adjust snd_cwnd
	 * accordingly.
	 */
	tp->snd_cwnd = imax(maxseg, tp->snd_nxt - tp->snd_recover +
		tp->sackhint.sack_bytes_rexmit + (snd_cnt * maxseg));
	tp->t_flags |= TF_ACKNOW;
	(void) tcp_output(tp);
}

/*
 * On a partial ack arrives, force the retransmission of the