1 // SPDX-License-Identifier: GPL-2.0-only
2 /*
3 * TCP Veno congestion control
4 *
5 * This is based on the congestion detection/avoidance scheme described in
6 * C. P. Fu, S. C. Liew.
7 * "TCP Veno: TCP Enhancement for Transmission over Wireless Access Networks."
8 * IEEE Journal on Selected Areas in Communication,
9 * Feb. 2003.
10 * See https://www.ie.cuhk.edu.hk/fileadmin/staff_upload/soung/Journal/J3.pdf
11 */
12
13 #include <linux/mm.h>
14 #include <linux/module.h>
15 #include <linux/skbuff.h>
16 #include <linux/inet_diag.h>
17
18 #include <net/tcp.h>
19
20 /* Default values of the Veno variables, in fixed-point representation
21 * with V_PARAM_SHIFT bits to the right of the binary point.
22 */
23 #define V_PARAM_SHIFT 1
24 static const int beta = 3 << V_PARAM_SHIFT;
25
26 /* Veno variables */
27 struct veno {
28 u8 doing_veno_now; /* if true, do veno for this rtt */
29 u16 cntrtt; /* # of rtts measured within last rtt */
30 u32 minrtt; /* min of rtts measured within last rtt (in usec) */
31 u32 basertt; /* the min of all Veno rtt measurements seen (in usec) */
32 u32 inc; /* decide whether to increase cwnd */
33 u32 diff; /* calculate the diff rate */
34 };
35
36 /* There are several situations when we must "re-start" Veno:
37 *
38 * o when a connection is established
39 * o after an RTO
40 * o after fast recovery
41 * o when we send a packet and there is no outstanding
42 * unacknowledged data (restarting an idle connection)
43 *
44 */
45 static inline void veno_enable(struct sock *sk)
46 {
47 struct veno *veno = inet_csk_ca(sk);
48
49 /* turn on Veno */
50 veno->doing_veno_now = 1;
51
52 veno->minrtt = 0x7fffffff;
53 }
54
55 static inline void veno_disable(struct sock *sk)
56 {
57 struct veno *veno = inet_csk_ca(sk);
58
59 /* turn off Veno */
60 veno->doing_veno_now = 0;
61 }
62
63 static void tcp_veno_init(struct sock *sk)
64 {
65 struct veno *veno = inet_csk_ca(sk);
66
67 veno->basertt = 0x7fffffff;
68 veno->inc = 1;
69 veno_enable(sk);
70 }
71
72 /* Do rtt sampling needed for Veno. */
73 static void tcp_veno_pkts_acked(struct sock *sk,
74 const struct ack_sample *sample)
75 {
76 struct veno *veno = inet_csk_ca(sk);
77 u32 vrtt;
78
79 if (sample->rtt_us < 0)
80 return;
81
82 /* Never allow zero rtt or baseRTT */
83 vrtt = sample->rtt_us + 1;
84
85 /* Filter to find propagation delay: */
86 if (vrtt < veno->basertt)
87 veno->basertt = vrtt;
88
89 /* Find the min rtt during the last rtt to find
90 * the current prop. delay + queuing delay:
91 */
92 veno->minrtt = min(veno->minrtt, vrtt);
93 veno->cntrtt++;
94 }
95
96 static void tcp_veno_state(struct sock *sk, u8 ca_state)
97 {
98 if (ca_state == TCP_CA_Open)
99 veno_enable(sk);
100 else
101 veno_disable(sk);
102 }
103
104 /*
105 * If the connection is idle and we are restarting,
106 * then we don't want to do any Veno calculations
107 * until we get fresh rtt samples. So when we
108 * restart, we reset our Veno state to a clean
109 * state. After we get acks for this flight of
110 * packets, _then_ we can make Veno calculations
111 * again.
112 */
113 static void tcp_veno_cwnd_event(struct sock *sk, enum tcp_ca_event event)
114 {
115 if (event == CA_EVENT_CWND_RESTART || event == CA_EVENT_TX_START)
116 tcp_veno_init(sk);
117 }
118
119 static void tcp_veno_cong_avoid(struct sock *sk, u32 ack, u32 acked)
120 {
121 struct tcp_sock *tp = tcp_sk(sk);
122 struct veno *veno = inet_csk_ca(sk);
123
124 if (!veno->doing_veno_now) {
125 tcp_reno_cong_avoid(sk, ack, acked);
126 return;
127 }
128
129 /* limited by applications */
130 if (!tcp_is_cwnd_limited(sk))
131 return;
132
133 /* We do the Veno calculations only if we got enough rtt samples */
134 if (veno->cntrtt <= 2) {
135 /* We don't have enough rtt samples to do the Veno
136 * calculation, so we'll behave like Reno.
137 */
138 tcp_reno_cong_avoid(sk, ack, acked);
139 } else {
140 u64 target_cwnd;
141 u32 rtt;
142
143 /* We have enough rtt samples, so, using the Veno
144 * algorithm, we determine the state of the network.
145 */
146
147 rtt = veno->minrtt;
148
149 target_cwnd = (u64)tcp_snd_cwnd(tp) * veno->basertt;
150 target_cwnd <<= V_PARAM_SHIFT;
151 do_div(target_cwnd, rtt);
152
153 veno->diff = (tcp_snd_cwnd(tp) << V_PARAM_SHIFT) - target_cwnd;
154
155 if (tcp_in_slow_start(tp)) {
156 /* Slow start. */
157 acked = tcp_slow_start(tp, acked);
158 if (!acked)
159 goto done;
160 }
161
162 /* Congestion avoidance. */
163 if (veno->diff < beta) {
164 /* In the "non-congestive state", increase cwnd
165 * every rtt.
166 */
167 tcp_cong_avoid_ai(tp, tcp_snd_cwnd(tp), acked);
168 } else {
169 /* In the "congestive state", increase cwnd
170 * every other rtt.
171 */
172 if (tp->snd_cwnd_cnt >= tcp_snd_cwnd(tp)) {
173 if (veno->inc &&
174 tcp_snd_cwnd(tp) < tp->snd_cwnd_clamp) {
175 tcp_snd_cwnd_set(tp, tcp_snd_cwnd(tp) + 1);
176 veno->inc = 0;
177 } else
178 veno->inc = 1;
179 tp->snd_cwnd_cnt = 0;
180 } else
181 tp->snd_cwnd_cnt += acked;
182 }
183 done:
184 if (tcp_snd_cwnd(tp) < 2)
185 tcp_snd_cwnd_set(tp, 2);
186 else if (tcp_snd_cwnd(tp) > tp->snd_cwnd_clamp)
187 tcp_snd_cwnd_set(tp, tp->snd_cwnd_clamp);
188 }
189 /* Wipe the slate clean for the next rtt. */
190 /* veno->cntrtt = 0; */
191 veno->minrtt = 0x7fffffff;
192 }
193
194 /* Veno MD phase */
195 static u32 tcp_veno_ssthresh(struct sock *sk)
196 {
197 const struct tcp_sock *tp = tcp_sk(sk);
198 struct veno *veno = inet_csk_ca(sk);
199
200 if (veno->diff < beta)
201 /* in "non-congestive state", cut cwnd by 1/5 */
202 return max(tcp_snd_cwnd(tp) * 4 / 5, 2U);
203 else
204 /* in "congestive state", cut cwnd by 1/2 */
205 return max(tcp_snd_cwnd(tp) >> 1U, 2U);
206 }
207
208 static struct tcp_congestion_ops tcp_veno __read_mostly = {
209 .init = tcp_veno_init,
210 .ssthresh = tcp_veno_ssthresh,
211 .undo_cwnd = tcp_reno_undo_cwnd,
212 .cong_avoid = tcp_veno_cong_avoid,
213 .pkts_acked = tcp_veno_pkts_acked,
214 .set_state = tcp_veno_state,
215 .cwnd_event = tcp_veno_cwnd_event,
216
217 .owner = THIS_MODULE,
218 .name = "veno",
219 };
220
221 static int __init tcp_veno_register(void)
222 {
223 BUILD_BUG_ON(sizeof(struct veno) > ICSK_CA_PRIV_SIZE);
224 tcp_register_congestion_control(&tcp_veno);
225 return 0;
226 }
227
228 static void __exit tcp_veno_unregister(void)
229 {
230 tcp_unregister_congestion_control(&tcp_veno);
231 }
232
233 module_init(tcp_veno_register);
234 module_exit(tcp_veno_unregister);
235
236 MODULE_AUTHOR("Bin Zhou, Cheng Peng Fu");
237 MODULE_LICENSE("GPL");
238 MODULE_DESCRIPTION("TCP Veno");
239
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