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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.
9 * See http://www.ntu.edu.sg/home5/ZHOU0022/papers/CPFu03a.pdf
10 */
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 */
33};
34
35/* There are several situations when we must "re-start" Veno:
36 *
37 * o when a connection is established
38 * o after an RTO
39 * o after fast recovery
40 * o when we send a packet and there is no outstanding
41 * unacknowledged data (restarting an idle connection)
42 *
43 */
44static inline void veno_enable(struct sock *sk)
45{
46 struct veno *veno = inet_csk_ca(sk);
47
48 /* turn on Veno */
49 veno->doing_veno_now = 1;
50
51 veno->minrtt = 0x7fffffff;
52}
53
54static inline void veno_disable(struct sock *sk)
55{
56 struct veno *veno = inet_csk_ca(sk);
57
58 /* turn off Veno */
59 veno->doing_veno_now = 0;
60}
61
62static void tcp_veno_init(struct sock *sk)
63{
64 struct veno *veno = inet_csk_ca(sk);
65
66 veno->basertt = 0x7fffffff;
67 veno->inc = 1;
68 veno_enable(sk);
69}
70
71/* Do rtt sampling needed for Veno. */
72static void tcp_veno_rtt_calc(struct sock *sk, u32 usrtt)
73{
74 struct veno *veno = inet_csk_ca(sk);
75 u32 vrtt = usrtt + 1; /* Never allow zero rtt or basertt */
76
77 /* Filter to find propagation delay: */
78 if (vrtt < veno->basertt)
79 veno->basertt = vrtt;
80
81 /* Find the min rtt during the last rtt to find
82 * the current prop. delay + queuing delay:
83 */
84 veno->minrtt = min(veno->minrtt, vrtt);
85 veno->cntrtt++;
86}
87
88static void tcp_veno_state(struct sock *sk, u8 ca_state)
89{
90 if (ca_state == TCP_CA_Open)
91 veno_enable(sk);
92 else
93 veno_disable(sk);
94}
95
96/*
97 * If the connection is idle and we are restarting,
98 * then we don't want to do any Veno calculations
99 * until we get fresh rtt samples. So when we
100 * restart, we reset our Veno state to a clean
101 * state. After we get acks for this flight of
102 * packets, _then_ we can make Veno calculations
103 * again.
104 */
105static void tcp_veno_cwnd_event(struct sock *sk, enum tcp_ca_event event)
106{
107 if (event == CA_EVENT_CWND_RESTART || event == CA_EVENT_TX_START)
108 tcp_veno_init(sk);
109}
110
111static void tcp_veno_cong_avoid(struct sock *sk, u32 ack,
112 u32 seq_rtt, u32 in_flight, int flag)
113{
114 struct tcp_sock *tp = tcp_sk(sk);
115 struct veno *veno = inet_csk_ca(sk);
116
117 if (!veno->doing_veno_now)
118 return tcp_reno_cong_avoid(sk, ack, seq_rtt, in_flight, flag);
119
120 /* limited by applications */
121 if (!tcp_is_cwnd_limited(sk, in_flight))
122 return;
123
124 /* We do the Veno calculations only if we got enough rtt samples */
125 if (veno->cntrtt <= 2) {
126 /* We don't have enough rtt samples to do the Veno
127 * calculation, so we'll behave like Reno.
128 */
129 tcp_reno_cong_avoid(sk, ack, seq_rtt, in_flight, flag);
130 } else {
131 u32 rtt, target_cwnd;
132
133 /* We have enough rtt samples, so, using the Veno
134 * algorithm, we determine the state of the network.
135 */
136
137 rtt = veno->minrtt;
138
139 target_cwnd = ((tp->snd_cwnd * veno->basertt)
140 << V_PARAM_SHIFT) / rtt;
141
142 veno->diff = (tp->snd_cwnd << V_PARAM_SHIFT) - target_cwnd;
143
144 if (tp->snd_cwnd <= tp->snd_ssthresh) {
145 /* Slow start. */
146 tcp_slow_start(tp);
147 } else {
148 /* Congestion avoidance. */
149 if (veno->diff < beta) {
150 /* In the "non-congestive state", increase cwnd
151 * every rtt.
152 */
153 if (tp->snd_cwnd_cnt >= tp->snd_cwnd) {
154 if (tp->snd_cwnd < tp->snd_cwnd_clamp)
155 tp->snd_cwnd++;
156 tp->snd_cwnd_cnt = 0;
157 } else
158 tp->snd_cwnd_cnt++;
159 } else {
160 /* In the "congestive state", increase cwnd
161 * every other rtt.
162 */
163 if (tp->snd_cwnd_cnt >= tp->snd_cwnd) {
164 if (veno->inc
165 && tp->snd_cwnd <
166 tp->snd_cwnd_clamp) {
167 tp->snd_cwnd++;
168 veno->inc = 0;
169 } else
170 veno->inc = 1;
171 tp->snd_cwnd_cnt = 0;
172 } else
173 tp->snd_cwnd_cnt++;
174 }
175
176 }
177 if (tp->snd_cwnd < 2)
178 tp->snd_cwnd = 2;
179 else if (tp->snd_cwnd > tp->snd_cwnd_clamp)
180 tp->snd_cwnd = tp->snd_cwnd_clamp;
181 }
182 /* Wipe the slate clean for the next rtt. */
183 /* veno->cntrtt = 0; */
184 veno->minrtt = 0x7fffffff;
185}
186
187/* Veno MD phase */
188static u32 tcp_veno_ssthresh(struct sock *sk)
189{
190 const struct tcp_sock *tp = tcp_sk(sk);
191 struct veno *veno = inet_csk_ca(sk);
192
193 if (veno->diff < beta)
194 /* in "non-congestive state", cut cwnd by 1/5 */
195 return max(tp->snd_cwnd * 4 / 5, 2U);
196 else
197 /* in "congestive state", cut cwnd by 1/2 */
198 return max(tp->snd_cwnd >> 1U, 2U);
199}
200
Bin Zhou76f10172006-06-05 17:28:30 -0700201static struct tcp_congestion_ops tcp_veno = {
202 .init = tcp_veno_init,
203 .ssthresh = tcp_veno_ssthresh,
204 .cong_avoid = tcp_veno_cong_avoid,
Bin Zhou76f10172006-06-05 17:28:30 -0700205 .rtt_sample = tcp_veno_rtt_calc,
206 .set_state = tcp_veno_state,
207 .cwnd_event = tcp_veno_cwnd_event,
208
209 .owner = THIS_MODULE,
210 .name = "veno",
211};
212
213static int __init tcp_veno_register(void)
214{
Alexey Dobriyan74975d42006-08-25 17:10:33 -0700215 BUILD_BUG_ON(sizeof(struct veno) > ICSK_CA_PRIV_SIZE);
Bin Zhou76f10172006-06-05 17:28:30 -0700216 tcp_register_congestion_control(&tcp_veno);
217 return 0;
218}
219
220static void __exit tcp_veno_unregister(void)
221{
222 tcp_unregister_congestion_control(&tcp_veno);
223}
224
225module_init(tcp_veno_register);
226module_exit(tcp_veno_unregister);
227
228MODULE_AUTHOR("Bin Zhou, Cheng Peng Fu");
229MODULE_LICENSE("GPL");
230MODULE_DESCRIPTION("TCP Veno");