1 /*
2 * Binary Increase Congestion control for TCP
3 * Home page:
4 * http://netsrv.csc.ncsu.edu/twiki/bin/view/Main/BIC
5 * This is from the implementation of BICTCP in
6 * Lison-Xu, Kahaled Harfoush, and Injong Rhee.
7 * "Binary Increase Congestion Control for Fast, Long Distance
8 * Networks" in InfoComm 2004
9 * Available from:
10 * http://netsrv.csc.ncsu.edu/export/bitcp.pdf
11 *
12 * Unless BIC is enabled and congestion window is large
13 * this behaves the same as the original Reno.
14 */
15
16 #include <linux/mm.h>
17 #include <linux/module.h>
18 #include <net/tcp.h>
19
20
21 #define BICTCP_BETA_SCALE 1024 /* Scale factor beta calculation
22 * max_cwnd = snd_cwnd * beta
23 */
24 #define BICTCP_B 4 /*
25 * In binary search,
26 * go to point (max+min)/N
27 */
28
29 static int fast_convergence = 1;
30 static int max_increment = 16;
31 static int low_window = 14;
32 static int beta = 819; /* = 819/1024 (BICTCP_BETA_SCALE) */
33 static int initial_ssthresh;
34 static int smooth_part = 20;
35
36 module_param(fast_convergence, int, 0644);
37 MODULE_PARM_DESC(fast_convergence, "turn on/off fast convergence");
38 module_param(max_increment, int, 0644);
39 MODULE_PARM_DESC(max_increment, "Limit on increment allowed during binary search");
40 module_param(low_window, int, 0644);
41 MODULE_PARM_DESC(low_window, "lower bound on congestion window (for TCP friendliness)");
42 module_param(beta, int, 0644);
43 MODULE_PARM_DESC(beta, "beta for multiplicative increase");
44 module_param(initial_ssthresh, int, 0644);
45 MODULE_PARM_DESC(initial_ssthresh, "initial value of slow start threshold");
46 module_param(smooth_part, int, 0644);
47 MODULE_PARM_DESC(smooth_part, "log(B/(B*Smin))/log(B/(B-1))+B, # of RTT from Wmax-B to Wmax");
48
49
50 /* BIC TCP Parameters */
51 struct bictcp {
52 u32 cnt; /* increase cwnd by 1 after ACKs */
53 u32 last_max_cwnd; /* last maximum snd_cwnd */
54 u32 loss_cwnd; /* congestion window at last loss */
55 u32 last_cwnd; /* the last snd_cwnd */
56 u32 last_time; /* time when updated last_cwnd */
57 u32 epoch_start; /* beginning of an epoch */
58 #define ACK_RATIO_SHIFT 4
59 u32 delayed_ack; /* estimate the ratio of Packets/ACKs << 4 */
60 };
61
62 static inline void bictcp_reset(struct bictcp *ca)
63 {
64 ca->cnt = 0;
65 ca->last_max_cwnd = 0;
66 ca->loss_cwnd = 0;
67 ca->last_cwnd = 0;
68 ca->last_time = 0;
69 ca->epoch_start = 0;
70 ca->delayed_ack = 2 << ACK_RATIO_SHIFT;
71 }
72
73 static void bictcp_init(struct sock *sk)
74 {
75 bictcp_reset(inet_csk_ca(sk));
76 if (initial_ssthresh)
77 tcp_sk(sk)->snd_ssthresh = initial_ssthresh;
78 }
79
80 /*
81 * Compute congestion window to use.
82 */
83 static inline void bictcp_update(struct bictcp *ca, u32 cwnd)
84 {
85 if (ca->last_cwnd == cwnd &&
86 (s32)(tcp_time_stamp - ca->last_time) <= HZ / 32)
87 return;
88
89 ca->last_cwnd = cwnd;
90 ca->last_time = tcp_time_stamp;
91
92 if (ca->epoch_start == 0) /* record the beginning of an epoch */
93 ca->epoch_start = tcp_time_stamp;
94
95 /* start off normal */
96 if (cwnd <= low_window) {
97 ca->cnt = cwnd;
98 return;
99 }
100
101 /* binary increase */
102 if (cwnd < ca->last_max_cwnd) {
103 __u32 dist = (ca->last_max_cwnd - cwnd)
104 / BICTCP_B;
105
106 if (dist > max_increment)
107 /* linear increase */
108 ca->cnt = cwnd / max_increment;
109 else if (dist <= 1U)
110 /* binary search increase */
111 ca->cnt = (cwnd * smooth_part) / BICTCP_B;
112 else
113 /* binary search increase */
114 ca->cnt = cwnd / dist;
115 } else {
116 /* slow start AMD linear increase */
117 if (cwnd < ca->last_max_cwnd + BICTCP_B)
118 /* slow start */
119 ca->cnt = (cwnd * smooth_part) / BICTCP_B;
120 else if (cwnd < ca->last_max_cwnd + max_increment*(BICTCP_B-1))
121 /* slow start */
122 ca->cnt = (cwnd * (BICTCP_B-1))
123 / (cwnd - ca->last_max_cwnd);
124 else
125 /* linear increase */
126 ca->cnt = cwnd / max_increment;
127 }
128
129 /* if in slow start or link utilization is very low */
130 if (ca->loss_cwnd == 0) {
131 if (ca->cnt > 20) /* increase cwnd 5% per RTT */
132 ca->cnt = 20;
133 }
134
135 ca->cnt = (ca->cnt << ACK_RATIO_SHIFT) / ca->delayed_ack;
136 if (ca->cnt == 0) /* cannot be zero */
137 ca->cnt = 1;
138 }
139
140 static void bictcp_cong_avoid(struct sock *sk, u32 ack, u32 in_flight)
141 {
142 struct tcp_sock *tp = tcp_sk(sk);
143 struct bictcp *ca = inet_csk_ca(sk);
144
145 if (!tcp_is_cwnd_limited(sk, in_flight))
146 return;
147
148 if (tp->snd_cwnd <= tp->snd_ssthresh)
149 tcp_slow_start(tp);
150 else {
151 bictcp_update(ca, tp->snd_cwnd);
152
153 /* In dangerous area, increase slowly.
154 * In theory this is tp->snd_cwnd += 1 / tp->snd_cwnd
155 */
156 if (tp->snd_cwnd_cnt >= ca->cnt) {
157 if (tp->snd_cwnd < tp->snd_cwnd_clamp)
158 tp->snd_cwnd++;
159 tp->snd_cwnd_cnt = 0;
160 } else
161 tp->snd_cwnd_cnt++;
162 }
163
164 }
165
166 /*
167 * behave like Reno until low_window is reached,
168 * then increase congestion window slowly
169 */
170 static u32 bictcp_recalc_ssthresh(struct sock *sk)
171 {
172 const struct tcp_sock *tp = tcp_sk(sk);
173 struct bictcp *ca = inet_csk_ca(sk);
174
175 ca->epoch_start = 0; /* end of epoch */
176
177 /* Wmax and fast convergence */
178 if (tp->snd_cwnd < ca->last_max_cwnd && fast_convergence)
179 ca->last_max_cwnd = (tp->snd_cwnd * (BICTCP_BETA_SCALE + beta))
180 / (2 * BICTCP_BETA_SCALE);
181 else
182 ca->last_max_cwnd = tp->snd_cwnd;
183
184 ca->loss_cwnd = tp->snd_cwnd;
185
186
187 if (tp->snd_cwnd <= low_window)
188 return max(tp->snd_cwnd >> 1U, 2U);
189 else
190 return max((tp->snd_cwnd * beta) / BICTCP_BETA_SCALE, 2U);
191 }
192
193 static u32 bictcp_undo_cwnd(struct sock *sk)
194 {
195 const struct tcp_sock *tp = tcp_sk(sk);
196 const struct bictcp *ca = inet_csk_ca(sk);
197 return max(tp->snd_cwnd, ca->last_max_cwnd);
198 }
199
200 static void bictcp_state(struct sock *sk, u8 new_state)
201 {
202 if (new_state == TCP_CA_Loss)
203 bictcp_reset(inet_csk_ca(sk));
204 }
205
206 /* Track delayed acknowledgment ratio using sliding window
207 * ratio = (15*ratio + sample) / 16
208 */
209 static void bictcp_acked(struct sock *sk, u32 cnt, s32 rtt)
210 {
211 const struct inet_connection_sock *icsk = inet_csk(sk);
212
213 if (icsk->icsk_ca_state == TCP_CA_Open) {
214 struct bictcp *ca = inet_csk_ca(sk);
215 cnt -= ca->delayed_ack >> ACK_RATIO_SHIFT;
216 ca->delayed_ack += cnt;
217 }
218 }
219
220
221 static struct tcp_congestion_ops bictcp = {
222 .init = bictcp_init,
223 .ssthresh = bictcp_recalc_ssthresh,
224 .cong_avoid = bictcp_cong_avoid,
225 .set_state = bictcp_state,
226 .undo_cwnd = bictcp_undo_cwnd,
227 .pkts_acked = bictcp_acked,
228 .owner = THIS_MODULE,
229 .name = "bic",
230 };
231
232 static int __init bictcp_register(void)
233 {
234 BUILD_BUG_ON(sizeof(struct bictcp) > ICSK_CA_PRIV_SIZE);
235 return tcp_register_congestion_control(&bictcp);
236 }
237
238 static void __exit bictcp_unregister(void)
239 {
240 tcp_unregister_congestion_control(&bictcp);
241 }
242
243 module_init(bictcp_register);
244 module_exit(bictcp_unregister);
245
246 MODULE_AUTHOR("Stephen Hemminger");
247 MODULE_LICENSE("GPL");
248 MODULE_DESCRIPTION("BIC TCP");
249
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