1 // SPDX-License-Identifier: GPL-2.0-only
3  * TCP Westwood+: end-to-end bandwidth estimation for TCP
10  * - Mascolo S, Casetti, M. Gerla et al.
13  * - A. Grieco, s. Mascolo
17  * - A. Dell'Aera, L. Grieco, S. Mascolo.
18  *   "Linux 2.4 Implementation of Westwood+ TCP with Rate-Halving :
21  * Westwood+ employs end-to-end bandwidth measurement to set cwnd and
43 	u8     reset_rtt_min;    /* Reset RTT min to next RTT sample*/
55  * information about RTTmin at this time so we simply set it to
65 	w->bk = 0;  in tcp_westwood_init()
66 	w->bw_ns_est = 0;  in tcp_westwood_init()
67 	w->bw_est = 0;  in tcp_westwood_init()
68 	w->accounted = 0;  in tcp_westwood_init()
69 	w->cumul_ack = 0;  in tcp_westwood_init()
70 	w->reset_rtt_min = 1;  in tcp_westwood_init()
71 	w->rtt_min = w->rtt = TCP_WESTWOOD_INIT_RTT;  in tcp_westwood_init()
72 	w->rtt_win_sx = tcp_jiffies32;  in tcp_westwood_init()
73 	w->snd_una = tcp_sk(sk)->snd_una;  in tcp_westwood_init()
74 	w->first_ack = 1;  in tcp_westwood_init()
79  * Low-pass filter. Implemented using constant coefficients.
88 	/* If the filter is empty fill it with the first sample of bandwidth  */  in westwood_filter()
89 	if (w->bw_ns_est == 0 && w->bw_est == 0) {  in westwood_filter()
90 		w->bw_ns_est = w->bk / delta;  in westwood_filter()
91 		w->bw_est = w->bw_ns_est;  in westwood_filter()
93 		w->bw_ns_est = westwood_do_filter(w->bw_ns_est, w->bk / delta);  in westwood_filter()
94 		w->bw_est = westwood_do_filter(w->bw_est, w->bw_ns_est);  in westwood_filter()
101  * but all westwood needs is the last sample of srtt.
104 				    const struct ack_sample *sample)  in tcp_westwood_pkts_acked()  argument
108 	if (sample->rtt_us > 0)  in tcp_westwood_pkts_acked()
109 		w->rtt = usecs_to_jiffies(sample->rtt_us);  in tcp_westwood_pkts_acked()
120 	s32 delta = tcp_jiffies32 - w->rtt_win_sx;  in westwood_update_window()
122 	/* Initialize w->snd_una with the first acked sequence number in order  in westwood_update_window()
123 	 * to fix mismatch between tp->snd_una and w->snd_una for the first  in westwood_update_window()
124 	 * bandwidth sample  in westwood_update_window()
126 	if (w->first_ack) {  in westwood_update_window()
127 		w->snd_una = tcp_sk(sk)->snd_una;  in westwood_update_window()
128 		w->first_ack = 0;  in westwood_update_window()
132 	 * See if a RTT-window has passed.  in westwood_update_window()
134 	 * 50ms we don't filter but we continue 'building the sample'.  in westwood_update_window()
136 	 * time intervals is better to avoid...  in westwood_update_window()
140 	if (w->rtt && delta > max_t(u32, w->rtt, TCP_WESTWOOD_RTT_MIN)) {  in westwood_update_window()
143 		w->bk = 0;  in westwood_update_window()
144 		w->rtt_win_sx = tcp_jiffies32;  in westwood_update_window()
150 	if (w->reset_rtt_min) {  in update_rtt_min()
151 		w->rtt_min = w->rtt;  in update_rtt_min()
152 		w->reset_rtt_min = 0;  in update_rtt_min()
154 		w->rtt_min = min(w->rtt, w->rtt_min);  in update_rtt_min()
170 	w->bk += tp->snd_una - w->snd_una;  in westwood_fast_bw()
171 	w->snd_una = tp->snd_una;  in westwood_fast_bw()
185 	w->cumul_ack = tp->snd_una - w->snd_una;  in westwood_acked_count()
188 	 * tp->snd_una.  in westwood_acked_count()
190 	if (!w->cumul_ack) {  in westwood_acked_count()
191 		w->accounted += tp->mss_cache;  in westwood_acked_count()
192 		w->cumul_ack = tp->mss_cache;  in westwood_acked_count()
195 	if (w->cumul_ack > tp->mss_cache) {  in westwood_acked_count()
197 		if (w->accounted >= w->cumul_ack) {  in westwood_acked_count()
198 			w->accounted -= w->cumul_ack;  in westwood_acked_count()
199 			w->cumul_ack = tp->mss_cache;  in westwood_acked_count()
201 			w->cumul_ack -= w->accounted;  in westwood_acked_count()
202 			w->accounted = 0;  in westwood_acked_count()
206 	w->snd_una = tp->snd_una;  in westwood_acked_count()
208 	return w->cumul_ack;  in westwood_acked_count()
222 	return max_t(u32, (w->bw_est * w->rtt_min) / tp->mss_cache, 2);  in tcp_westwood_bw_rttmin()
231 		w->bk += westwood_acked_count(sk);  in tcp_westwood_ack()
247 		tp->snd_cwnd = tp->snd_ssthresh = tcp_westwood_bw_rttmin(sk);  in tcp_westwood_event()
250 		tp->snd_ssthresh = tcp_westwood_bw_rttmin(sk);  in tcp_westwood_event()
252 		w->reset_rtt_min = 1;  in tcp_westwood_event()
266 	if (ext & (1 << (INET_DIAG_VEGASINFO - 1))) {  in tcp_westwood_info()
267 		info->vegas.tcpv_enabled = 1;  in tcp_westwood_info()
268 		info->vegas.tcpv_rttcnt	= 0;  in tcp_westwood_info()
269 		info->vegas.tcpv_rtt	= jiffies_to_usecs(ca->rtt);  in tcp_westwood_info()
270 		info->vegas.tcpv_minrtt	= jiffies_to_usecs(ca->rtt_min);  in tcp_westwood_info()