2 * Binary Increase Congestion control for TCP
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
10 * http://netsrv.csc.ncsu.edu/export/bitcp.pdf
12 * Unless BIC is enabled and congestion window is large
13 * this behaves the same as the original Reno.
17 #include <linux/module.h>
21 #define BICTCP_BETA_SCALE 1024 /* Scale factor beta calculation
22 * max_cwnd = snd_cwnd * beta
26 * go to point (max+min)/N
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;
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");
50 /* BIC TCP Parameters */
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 */
62 static inline void bictcp_reset(struct bictcp *ca)
65 ca->last_max_cwnd = 0;
70 ca->delayed_ack = 2 << ACK_RATIO_SHIFT;
73 static void bictcp_init(struct sock *sk)
75 bictcp_reset(inet_csk_ca(sk));
77 tcp_sk(sk)->snd_ssthresh = initial_ssthresh;
81 * Compute congestion window to use.
83 static inline void bictcp_update(struct bictcp *ca, u32 cwnd)
85 if (ca->last_cwnd == cwnd &&
86 (s32)(tcp_time_stamp - ca->last_time) <= HZ / 32)
90 ca->last_time = tcp_time_stamp;
92 if (ca->epoch_start == 0) /* record the beginning of an epoch */
93 ca->epoch_start = tcp_time_stamp;
95 /* start off normal */
96 if (cwnd <= low_window) {
101 /* binary increase */
102 if (cwnd < ca->last_max_cwnd) {
103 __u32 dist = (ca->last_max_cwnd - cwnd)
106 if (dist > max_increment)
107 /* linear increase */
108 ca->cnt = cwnd / max_increment;
110 /* binary search increase */
111 ca->cnt = (cwnd * smooth_part) / BICTCP_B;
113 /* binary search increase */
114 ca->cnt = cwnd / dist;
116 /* slow start AMD linear increase */
117 if (cwnd < ca->last_max_cwnd + BICTCP_B)
119 ca->cnt = (cwnd * smooth_part) / BICTCP_B;
120 else if (cwnd < ca->last_max_cwnd + max_increment*(BICTCP_B-1))
122 ca->cnt = (cwnd * (BICTCP_B-1))
123 / (cwnd - ca->last_max_cwnd);
125 /* linear increase */
126 ca->cnt = cwnd / max_increment;
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 */
135 ca->cnt = (ca->cnt << ACK_RATIO_SHIFT) / ca->delayed_ack;
136 if (ca->cnt == 0) /* cannot be zero */
140 static void bictcp_cong_avoid(struct sock *sk, u32 ack, u32 in_flight)
142 struct tcp_sock *tp = tcp_sk(sk);
143 struct bictcp *ca = inet_csk_ca(sk);
145 if (!tcp_is_cwnd_limited(sk, in_flight))
148 if (tp->snd_cwnd <= tp->snd_ssthresh)
151 bictcp_update(ca, tp->snd_cwnd);
152 tcp_cong_avoid_ai(tp, ca->cnt);
158 * behave like Reno until low_window is reached,
159 * then increase congestion window slowly
161 static u32 bictcp_recalc_ssthresh(struct sock *sk)
163 const struct tcp_sock *tp = tcp_sk(sk);
164 struct bictcp *ca = inet_csk_ca(sk);
166 ca->epoch_start = 0; /* end of epoch */
168 /* Wmax and fast convergence */
169 if (tp->snd_cwnd < ca->last_max_cwnd && fast_convergence)
170 ca->last_max_cwnd = (tp->snd_cwnd * (BICTCP_BETA_SCALE + beta))
171 / (2 * BICTCP_BETA_SCALE);
173 ca->last_max_cwnd = tp->snd_cwnd;
175 ca->loss_cwnd = tp->snd_cwnd;
178 if (tp->snd_cwnd <= low_window)
179 return max(tp->snd_cwnd >> 1U, 2U);
181 return max((tp->snd_cwnd * beta) / BICTCP_BETA_SCALE, 2U);
184 static u32 bictcp_undo_cwnd(struct sock *sk)
186 const struct tcp_sock *tp = tcp_sk(sk);
187 const struct bictcp *ca = inet_csk_ca(sk);
188 return max(tp->snd_cwnd, ca->last_max_cwnd);
191 static void bictcp_state(struct sock *sk, u8 new_state)
193 if (new_state == TCP_CA_Loss)
194 bictcp_reset(inet_csk_ca(sk));
197 /* Track delayed acknowledgment ratio using sliding window
198 * ratio = (15*ratio + sample) / 16
200 static void bictcp_acked(struct sock *sk, u32 cnt, s32 rtt)
202 const struct inet_connection_sock *icsk = inet_csk(sk);
204 if (icsk->icsk_ca_state == TCP_CA_Open) {
205 struct bictcp *ca = inet_csk_ca(sk);
206 cnt -= ca->delayed_ack >> ACK_RATIO_SHIFT;
207 ca->delayed_ack += cnt;
212 static struct tcp_congestion_ops bictcp = {
214 .ssthresh = bictcp_recalc_ssthresh,
215 .cong_avoid = bictcp_cong_avoid,
216 .set_state = bictcp_state,
217 .undo_cwnd = bictcp_undo_cwnd,
218 .pkts_acked = bictcp_acked,
219 .owner = THIS_MODULE,
223 static int __init bictcp_register(void)
225 BUILD_BUG_ON(sizeof(struct bictcp) > ICSK_CA_PRIV_SIZE);
226 return tcp_register_congestion_control(&bictcp);
229 static void __exit bictcp_unregister(void)
231 tcp_unregister_congestion_control(&bictcp);
234 module_init(bictcp_register);
235 module_exit(bictcp_unregister);
237 MODULE_AUTHOR("Stephen Hemminger");
238 MODULE_LICENSE("GPL");
239 MODULE_DESCRIPTION("BIC TCP");