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Bin Zhou76f10172006-06-05 17:28:30 -07001/*
2 * TCP Veno congestion control
3 *
4 * This is based on the congestion detection/avoidance scheme described in
5 * C. P. Fu, S. C. Liew.
6 * "TCP Veno: TCP Enhancement for Transmission over Wireless Access Networks."
7 * IEEE Journal on Selected Areas in Communication,
8 * Feb. 2003.
Justin P. Mattock631dd1a2010-10-18 11:03:14 +02009 * See http://www.ie.cuhk.edu.hk/fileadmin/staff_upload/soung/Journal/J3.pdf
Bin Zhou76f10172006-06-05 17:28:30 -070010 */
11
Bin Zhou76f10172006-06-05 17:28:30 -070012#include <linux/mm.h>
13#include <linux/module.h>
14#include <linux/skbuff.h>
15#include <linux/inet_diag.h>
16
17#include <net/tcp.h>
18
19/* Default values of the Veno variables, in fixed-point representation
20 * with V_PARAM_SHIFT bits to the right of the binary point.
21 */
22#define V_PARAM_SHIFT 1
23static const int beta = 3 << V_PARAM_SHIFT;
24
25/* Veno variables */
26struct veno {
27 u8 doing_veno_now; /* if true, do veno for this rtt */
28 u16 cntrtt; /* # of rtts measured within last rtt */
29 u32 minrtt; /* min of rtts measured within last rtt (in usec) */
30 u32 basertt; /* the min of all Veno rtt measurements seen (in usec) */
31 u32 inc; /* decide whether to increase cwnd */
32 u32 diff; /* calculate the diff rate */
Florian Westphal85f7e752016-11-21 14:18:37 +010033 u32 loss_cwnd; /* cwnd when loss occured */
Bin Zhou76f10172006-06-05 17:28:30 -070034};
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 */
45static 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
55static 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
63static 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. */
Lawrence Brakmo756ee172016-05-11 10:02:13 -070073static void tcp_veno_pkts_acked(struct sock *sk,
74 const struct ack_sample *sample)
Bin Zhou76f10172006-06-05 17:28:30 -070075{
76 struct veno *veno = inet_csk_ca(sk);
Stephen Hemminger164891a2007-04-23 22:26:16 -070077 u32 vrtt;
78
Lawrence Brakmo756ee172016-05-11 10:02:13 -070079 if (sample->rtt_us < 0)
Ilpo Järvinenb9ce2042007-06-15 15:08:43 -070080 return;
81
Stephen Hemminger164891a2007-04-23 22:26:16 -070082 /* Never allow zero rtt or baseRTT */
Lawrence Brakmo756ee172016-05-11 10:02:13 -070083 vrtt = sample->rtt_us + 1;
Bin Zhou76f10172006-06-05 17:28:30 -070084
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
96static 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 */
113static 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
Eric Dumazet24901552014-05-02 21:18:05 -0700119static void tcp_veno_cong_avoid(struct sock *sk, u32 ack, u32 acked)
Bin Zhou76f10172006-06-05 17:28:30 -0700120{
121 struct tcp_sock *tp = tcp_sk(sk);
122 struct veno *veno = inet_csk_ca(sk);
123
Harvey Harrisonab598592008-05-01 02:47:38 -0700124 if (!veno->doing_veno_now) {
Eric Dumazet24901552014-05-02 21:18:05 -0700125 tcp_reno_cong_avoid(sk, ack, acked);
Harvey Harrisonab598592008-05-01 02:47:38 -0700126 return;
127 }
Bin Zhou76f10172006-06-05 17:28:30 -0700128
129 /* limited by applications */
Eric Dumazet24901552014-05-02 21:18:05 -0700130 if (!tcp_is_cwnd_limited(sk))
Bin Zhou76f10172006-06-05 17:28:30 -0700131 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 */
Eric Dumazet24901552014-05-02 21:18:05 -0700138 tcp_reno_cong_avoid(sk, ack, acked);
Bin Zhou76f10172006-06-05 17:28:30 -0700139 } else {
Lachlan Andrew15913112008-04-30 01:04:03 -0700140 u64 target_cwnd;
141 u32 rtt;
Bin Zhou76f10172006-06-05 17:28:30 -0700142
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
Christoph Paasch45a07692014-07-29 12:07:27 +0200149 target_cwnd = (u64)tp->snd_cwnd * veno->basertt;
Lachlan Andrew15913112008-04-30 01:04:03 -0700150 target_cwnd <<= V_PARAM_SHIFT;
151 do_div(target_cwnd, rtt);
Bin Zhou76f10172006-06-05 17:28:30 -0700152
153 veno->diff = (tp->snd_cwnd << V_PARAM_SHIFT) - target_cwnd;
154
Yuchung Cheng071d5082015-07-09 13:16:29 -0700155 if (tcp_in_slow_start(tp)) {
Bin Zhou76f10172006-06-05 17:28:30 -0700156 /* Slow start. */
Yuchung Cheng9f9843a72013-10-31 11:07:31 -0700157 tcp_slow_start(tp, acked);
Bin Zhou76f10172006-06-05 17:28:30 -0700158 } else {
159 /* Congestion avoidance. */
160 if (veno->diff < beta) {
161 /* In the "non-congestive state", increase cwnd
162 * every rtt.
163 */
Neal Cardwelle73ebb02015-01-28 20:01:35 -0500164 tcp_cong_avoid_ai(tp, tp->snd_cwnd, 1);
Bin Zhou76f10172006-06-05 17:28:30 -0700165 } else {
166 /* In the "congestive state", increase cwnd
167 * every other rtt.
168 */
169 if (tp->snd_cwnd_cnt >= tp->snd_cwnd) {
Joe Perches9d4fb272009-11-23 10:41:23 -0800170 if (veno->inc &&
171 tp->snd_cwnd < tp->snd_cwnd_clamp) {
Bin Zhou76f10172006-06-05 17:28:30 -0700172 tp->snd_cwnd++;
173 veno->inc = 0;
174 } else
175 veno->inc = 1;
176 tp->snd_cwnd_cnt = 0;
177 } else
178 tp->snd_cwnd_cnt++;
179 }
Bin Zhou76f10172006-06-05 17:28:30 -0700180 }
181 if (tp->snd_cwnd < 2)
182 tp->snd_cwnd = 2;
183 else if (tp->snd_cwnd > tp->snd_cwnd_clamp)
184 tp->snd_cwnd = tp->snd_cwnd_clamp;
185 }
186 /* Wipe the slate clean for the next rtt. */
187 /* veno->cntrtt = 0; */
188 veno->minrtt = 0x7fffffff;
189}
190
191/* Veno MD phase */
192static u32 tcp_veno_ssthresh(struct sock *sk)
193{
194 const struct tcp_sock *tp = tcp_sk(sk);
195 struct veno *veno = inet_csk_ca(sk);
196
Florian Westphal85f7e752016-11-21 14:18:37 +0100197 veno->loss_cwnd = tp->snd_cwnd;
Bin Zhou76f10172006-06-05 17:28:30 -0700198 if (veno->diff < beta)
199 /* in "non-congestive state", cut cwnd by 1/5 */
200 return max(tp->snd_cwnd * 4 / 5, 2U);
201 else
202 /* in "congestive state", cut cwnd by 1/2 */
203 return max(tp->snd_cwnd >> 1U, 2U);
204}
205
Florian Westphal85f7e752016-11-21 14:18:37 +0100206static u32 tcp_veno_cwnd_undo(struct sock *sk)
207{
208 const struct veno *veno = inet_csk_ca(sk);
209
210 return max(tcp_sk(sk)->snd_cwnd, veno->loss_cwnd);
211}
212
Stephen Hemmingera252beb2011-03-10 00:40:17 -0800213static struct tcp_congestion_ops tcp_veno __read_mostly = {
Bin Zhou76f10172006-06-05 17:28:30 -0700214 .init = tcp_veno_init,
215 .ssthresh = tcp_veno_ssthresh,
Florian Westphal85f7e752016-11-21 14:18:37 +0100216 .undo_cwnd = tcp_veno_cwnd_undo,
Bin Zhou76f10172006-06-05 17:28:30 -0700217 .cong_avoid = tcp_veno_cong_avoid,
Stephen Hemminger164891a2007-04-23 22:26:16 -0700218 .pkts_acked = tcp_veno_pkts_acked,
Bin Zhou76f10172006-06-05 17:28:30 -0700219 .set_state = tcp_veno_state,
220 .cwnd_event = tcp_veno_cwnd_event,
221
222 .owner = THIS_MODULE,
223 .name = "veno",
224};
225
226static int __init tcp_veno_register(void)
227{
Alexey Dobriyan74975d42006-08-25 17:10:33 -0700228 BUILD_BUG_ON(sizeof(struct veno) > ICSK_CA_PRIV_SIZE);
Bin Zhou76f10172006-06-05 17:28:30 -0700229 tcp_register_congestion_control(&tcp_veno);
230 return 0;
231}
232
233static void __exit tcp_veno_unregister(void)
234{
235 tcp_unregister_congestion_control(&tcp_veno);
236}
237
238module_init(tcp_veno_register);
239module_exit(tcp_veno_unregister);
240
241MODULE_AUTHOR("Bin Zhou, Cheng Peng Fu");
242MODULE_LICENSE("GPL");
243MODULE_DESCRIPTION("TCP Veno");