Function rack_get_pacing_delay

freebsd/netinet/tcp_stacks/rack.c:11440–11654

}

static int32_t
rack_get_pacing_delay(struct tcp_rack *rack, struct tcpcb *tp, uint32_t len, struct rack_sendmap *rsm, uint32_t segsiz)
{
	struct rack_sendmap *lrsm;
	int32_t slot = 0;
	int err;

	if (rack->rc_always_pace == 0) {
		/*
		 * We use the most optimistic possible cwnd/srtt for
		 * sending calculations. This will make our
		 * calculation anticipate getting more through
		 * quicker then possible. But thats ok we don't want
		 * the peer to have a gap in data sending.
		 */
		uint32_t srtt, cwnd, tr_perms = 0;
		int32_t reduce = 0;

	old_method:
		/*
		 * We keep no precise pacing with the old method
		 * instead we use the pacer to mitigate bursts.
		 */
		rack->r_ctl.rc_agg_delayed = 0;
		rack->r_early = 0;
		rack->r_late = 0;
		rack->r_ctl.rc_agg_early = 0;
		if (rack->r_ctl.rc_rack_min_rtt)
			srtt = rack->r_ctl.rc_rack_min_rtt;
		else
			srtt = TICKS_2_MSEC((tp->t_srtt >> TCP_RTT_SHIFT));
		if (rack->r_ctl.rc_rack_largest_cwnd)
			cwnd = rack->r_ctl.rc_rack_largest_cwnd;
		else
			cwnd = rack->r_ctl.cwnd_to_use;
		tr_perms = cwnd / srtt;
		if (tr_perms == 0) {
			tr_perms = ctf_fixed_maxseg(tp);
		}
		/*
		 * Calculate how long this will take to drain, if
		 * the calculation comes out to zero, thats ok we
		 * will use send_a_lot to possibly spin around for
		 * more increasing tot_len_this_send to the point
		 * that its going to require a pace, or we hit the
		 * cwnd. Which in that case we are just waiting for
		 * a ACK.
		 */
		slot = len / tr_perms;
		/* Now do we reduce the time so we don't run dry? */
		if (slot && rack_slot_reduction) {
			reduce = (slot / rack_slot_reduction);
			if (reduce < slot) {
				slot -= reduce;
			} else
				slot = 0;
		}
		slot *=  HPTS_USEC_IN_MSEC;