1 // SPDX-License-Identifier: GPL-2.0-only
8  *    IEEE Journal on Selected Areas in Communication, 13(8):1465--1480,
15  *   o We do not change the loss detection or recovery mechanisms of
17  *     using fine-grained timers, NewReno, and FACK.
19  *     only every-other RTT during slow start, we increase during
22  *     we use the rate at which ACKs come back as the "actual"
24  *   o To speed convergence to the right rate, we set the cwnd
25  *     to achieve the right ("actual") rate when we exit slow start.
26  *   o To filter out the noise caused by delayed ACKs, we use the
29  *   o When the sender re-starts from idle, it waits until it has
55 /* There are several situations when we must "re-start" Vegas:
60  *  o when we send a packet and there is no outstanding
63  * In these circumstances we cannot do a Vegas calculation at the
64  * end of the first RTT, because any calculation we do is using
65  * stale info -- both the saved cwnd and congestion feedback are
68  * Instead we must wait until the completion of an RTT during
69  * which we actually receive ACKs.
76 	/* Begin taking Vegas samples next time we send something. */  in vegas_enable()
77 	vegas->doing_vegas_now = 1;  in vegas_enable()
80 	vegas->beg_snd_nxt = tp->snd_nxt;  in vegas_enable()
82 	vegas->cntRTT = 0;  in vegas_enable()
83 	vegas->minRTT = 0x7fffffff;  in vegas_enable()
91 	vegas->doing_vegas_now = 0;  in vegas_disable()
98 	vegas->baseRTT = 0x7fffffff;  in tcp_vegas_init()
104  * Basically we:
105  *   o min-filter RTT samples from within an RTT to get the current
106  *     propagation delay + queuing delay (we are min-filtering to try to
108  *   o min-filter RTT samples from a much longer window (forever for now)
109  *     to find the propagation delay (baseRTT)
116 	if (sample->rtt_us < 0)  in tcp_vegas_pkts_acked()
120 	vrtt = sample->rtt_us + 1;  in tcp_vegas_pkts_acked()
122 	/* Filter to find propagation delay: */  in tcp_vegas_pkts_acked()
123 	if (vrtt < vegas->baseRTT)  in tcp_vegas_pkts_acked()
124 		vegas->baseRTT = vrtt;  in tcp_vegas_pkts_acked()
127 	 * the current prop. delay + queuing delay:  in tcp_vegas_pkts_acked()
129 	vegas->minRTT = min(vegas->minRTT, vrtt);  in tcp_vegas_pkts_acked()
130 	vegas->cntRTT++;  in tcp_vegas_pkts_acked()
144  * If the connection is idle and we are restarting,
145  * then we don't want to do any Vegas calculations
146  * until we get fresh RTT samples.  So when we
147  * restart, we reset our Vegas state to a clean
148  * slate. After we get acks for this flight of
149  * packets, _then_ we can make Vegas calculations
162 	return  min(tp->snd_ssthresh, tcp_snd_cwnd(tp));  in tcp_vegas_ssthresh()
170 	if (!vegas->doing_vegas_now) {  in tcp_vegas_cong_avoid()
175 	if (after(ack, vegas->beg_snd_nxt)) {  in tcp_vegas_cong_avoid()
176 		/* Do the Vegas once-per-RTT cwnd adjustment. */  in tcp_vegas_cong_avoid()
178 		/* Save the extent of the current window so we can use this  in tcp_vegas_cong_avoid()
181 		vegas->beg_snd_nxt  = tp->snd_nxt;  in tcp_vegas_cong_avoid()
183 		/* We do the Vegas calculations only if we got enough RTT  in tcp_vegas_cong_avoid()
184 		 * samples that we can be reasonably sure that we got  in tcp_vegas_cong_avoid()
186 		 * If we only had 2 samples total,  in tcp_vegas_cong_avoid()
187 		 * then that means we're getting only 1 ACK per RTT, which  in tcp_vegas_cong_avoid()
189 		 * If  we have 3 samples, we should be OK.  in tcp_vegas_cong_avoid()
192 		if (vegas->cntRTT <= 2) {  in tcp_vegas_cong_avoid()
193 			/* We don't have enough RTT samples to do the Vegas  in tcp_vegas_cong_avoid()
194 			 * calculation, so we'll behave like Reno.  in tcp_vegas_cong_avoid()
201 			/* We have enough RTT samples, so, using the Vegas  in tcp_vegas_cong_avoid()
202 			 * algorithm, we determine if we should increase or  in tcp_vegas_cong_avoid()
206 			/* Pluck out the RTT we are using for the Vegas  in tcp_vegas_cong_avoid()
212 			rtt = vegas->minRTT;  in tcp_vegas_cong_avoid()
214 			/* Calculate the cwnd we should have, if we weren't  in tcp_vegas_cong_avoid()
220 			target_cwnd = (u64)tcp_snd_cwnd(tp) * vegas->baseRTT;  in tcp_vegas_cong_avoid()
223 			/* Calculate the difference between the window we had,  in tcp_vegas_cong_avoid()
224 			 * and the window we would like to have. This quantity  in tcp_vegas_cong_avoid()
227 			diff = tcp_snd_cwnd(tp) * (rtt-vegas->baseRTT) / vegas->baseRTT;  in tcp_vegas_cong_avoid()
237 				 * Then we add 1 because the integer  in tcp_vegas_cong_avoid()
243 				tp->snd_ssthresh = tcp_vegas_ssthresh(tp);  in tcp_vegas_cong_avoid()
251 				/* Figure out where we would like cwnd  in tcp_vegas_cong_avoid()
256 					 * we slow down.  in tcp_vegas_cong_avoid()
258 					tcp_snd_cwnd_set(tp, tcp_snd_cwnd(tp) - 1);  in tcp_vegas_cong_avoid()
259 					tp->snd_ssthresh  in tcp_vegas_cong_avoid()
262 					/* We don't have enough extra packets  in tcp_vegas_cong_avoid()
267 					/* Sending just as fast as we  in tcp_vegas_cong_avoid()
275 			else if (tcp_snd_cwnd(tp) > tp->snd_cwnd_clamp)  in tcp_vegas_cong_avoid()
276 				tcp_snd_cwnd_set(tp, tp->snd_cwnd_clamp);  in tcp_vegas_cong_avoid()
278 			tp->snd_ssthresh = tcp_current_ssthresh(sk);  in tcp_vegas_cong_avoid()
282 		vegas->cntRTT = 0;  in tcp_vegas_cong_avoid()
283 		vegas->minRTT = 0x7fffffff;  in tcp_vegas_cong_avoid()
296 	if (ext & (1 << (INET_DIAG_VEGASINFO - 1))) {  in tcp_vegas_get_info()
297 		info->vegas.tcpv_enabled = ca->doing_vegas_now;  in tcp_vegas_get_info()
298 		info->vegas.tcpv_rttcnt = ca->cntRTT;  in tcp_vegas_get_info()
299 		info->vegas.tcpv_rtt = ca->baseRTT;  in tcp_vegas_get_info()
300 		info->vegas.tcpv_minrtt = ca->minRTT;  in tcp_vegas_get_info()