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16#include <linux/mm.h>
17#include <linux/module.h>
18#include <net/tcp.h>
19
20
21#define BICTCP_BETA_SCALE 1024
22
23
24#define BICTCP_B 4
25
26
27
28
29static int fast_convergence = 1;
30static int max_increment = 16;
31static int low_window = 14;
32static int beta = 819;
33static int initial_ssthresh;
34static int smooth_part = 20;
35
36module_param(fast_convergence, int, 0644);
37MODULE_PARM_DESC(fast_convergence, "turn on/off fast convergence");
38module_param(max_increment, int, 0644);
39MODULE_PARM_DESC(max_increment, "Limit on increment allowed during binary search");
40module_param(low_window, int, 0644);
41MODULE_PARM_DESC(low_window, "lower bound on congestion window (for TCP friendliness)");
42module_param(beta, int, 0644);
43MODULE_PARM_DESC(beta, "beta for multiplicative increase");
44module_param(initial_ssthresh, int, 0644);
45MODULE_PARM_DESC(initial_ssthresh, "initial value of slow start threshold");
46module_param(smooth_part, int, 0644);
47MODULE_PARM_DESC(smooth_part, "log(B/(B*Smin))/log(B/(B-1))+B, # of RTT from Wmax-B to Wmax");
48
49
50
51struct bictcp {
52 u32 cnt;
53 u32 last_max_cwnd;
54 u32 loss_cwnd;
55 u32 last_cwnd;
56 u32 last_time;
57 u32 epoch_start;
58#define ACK_RATIO_SHIFT 4
59 u32 delayed_ack;
60};
61
62static inline void bictcp_reset(struct bictcp *ca)
63{
64 ca->cnt = 0;
65 ca->last_max_cwnd = 0;
66 ca->last_cwnd = 0;
67 ca->last_time = 0;
68 ca->epoch_start = 0;
69 ca->delayed_ack = 2 << ACK_RATIO_SHIFT;
70}
71
72static void bictcp_init(struct sock *sk)
73{
74 struct bictcp *ca = inet_csk_ca(sk);
75
76 bictcp_reset(ca);
77 ca->loss_cwnd = 0;
78
79 if (initial_ssthresh)
80 tcp_sk(sk)->snd_ssthresh = initial_ssthresh;
81}
82
83
84
85
86static inline void bictcp_update(struct bictcp *ca, u32 cwnd)
87{
88 if (ca->last_cwnd == cwnd &&
89 (s32)(tcp_time_stamp - ca->last_time) <= HZ / 32)
90 return;
91
92 ca->last_cwnd = cwnd;
93 ca->last_time = tcp_time_stamp;
94
95 if (ca->epoch_start == 0)
96 ca->epoch_start = tcp_time_stamp;
97
98
99 if (cwnd <= low_window) {
100 ca->cnt = cwnd;
101 return;
102 }
103
104
105 if (cwnd < ca->last_max_cwnd) {
106 __u32 dist = (ca->last_max_cwnd - cwnd)
107 / BICTCP_B;
108
109 if (dist > max_increment)
110
111 ca->cnt = cwnd / max_increment;
112 else if (dist <= 1U)
113
114 ca->cnt = (cwnd * smooth_part) / BICTCP_B;
115 else
116
117 ca->cnt = cwnd / dist;
118 } else {
119
120 if (cwnd < ca->last_max_cwnd + BICTCP_B)
121
122 ca->cnt = (cwnd * smooth_part) / BICTCP_B;
123 else if (cwnd < ca->last_max_cwnd + max_increment*(BICTCP_B-1))
124
125 ca->cnt = (cwnd * (BICTCP_B-1))
126 / (cwnd - ca->last_max_cwnd);
127 else
128
129 ca->cnt = cwnd / max_increment;
130 }
131
132
133 if (ca->last_max_cwnd == 0) {
134 if (ca->cnt > 20)
135 ca->cnt = 20;
136 }
137
138 ca->cnt = (ca->cnt << ACK_RATIO_SHIFT) / ca->delayed_ack;
139 if (ca->cnt == 0)
140 ca->cnt = 1;
141}
142
143static void bictcp_cong_avoid(struct sock *sk, u32 ack, u32 in_flight)
144{
145 struct tcp_sock *tp = tcp_sk(sk);
146 struct bictcp *ca = inet_csk_ca(sk);
147
148 if (!tcp_is_cwnd_limited(sk, in_flight))
149 return;
150
151 if (tp->snd_cwnd <= tp->snd_ssthresh)
152 tcp_slow_start(tp);
153 else {
154 bictcp_update(ca, tp->snd_cwnd);
155 tcp_cong_avoid_ai(tp, ca->cnt);
156 }
157
158}
159
160
161
162
163
164static u32 bictcp_recalc_ssthresh(struct sock *sk)
165{
166 const struct tcp_sock *tp = tcp_sk(sk);
167 struct bictcp *ca = inet_csk_ca(sk);
168
169 ca->epoch_start = 0;
170
171
172 if (tp->snd_cwnd < ca->last_max_cwnd && fast_convergence)
173 ca->last_max_cwnd = (tp->snd_cwnd * (BICTCP_BETA_SCALE + beta))
174 / (2 * BICTCP_BETA_SCALE);
175 else
176 ca->last_max_cwnd = tp->snd_cwnd;
177
178 ca->loss_cwnd = tp->snd_cwnd;
179
180
181 if (tp->snd_cwnd <= low_window)
182 return max(tp->snd_cwnd >> 1U, 2U);
183 else
184 return max((tp->snd_cwnd * beta) / BICTCP_BETA_SCALE, 2U);
185}
186
187static u32 bictcp_undo_cwnd(struct sock *sk)
188{
189 const struct tcp_sock *tp = tcp_sk(sk);
190 const struct bictcp *ca = inet_csk_ca(sk);
191 return max(tp->snd_cwnd, ca->loss_cwnd);
192}
193
194static void bictcp_state(struct sock *sk, u8 new_state)
195{
196 if (new_state == TCP_CA_Loss)
197 bictcp_reset(inet_csk_ca(sk));
198}
199
200
201
202
203static void bictcp_acked(struct sock *sk, u32 cnt, s32 rtt)
204{
205 const struct inet_connection_sock *icsk = inet_csk(sk);
206
207 if (icsk->icsk_ca_state == TCP_CA_Open) {
208 struct bictcp *ca = inet_csk_ca(sk);
209 cnt -= ca->delayed_ack >> ACK_RATIO_SHIFT;
210 ca->delayed_ack += cnt;
211 }
212}
213
214
215static struct tcp_congestion_ops bictcp __read_mostly = {
216 .init = bictcp_init,
217 .ssthresh = bictcp_recalc_ssthresh,
218 .cong_avoid = bictcp_cong_avoid,
219 .set_state = bictcp_state,
220 .undo_cwnd = bictcp_undo_cwnd,
221 .pkts_acked = bictcp_acked,
222 .owner = THIS_MODULE,
223 .name = "bic",
224};
225
226static int __init bictcp_register(void)
227{
228 BUILD_BUG_ON(sizeof(struct bictcp) > ICSK_CA_PRIV_SIZE);
229 return tcp_register_congestion_control(&bictcp);
230}
231
232static void __exit bictcp_unregister(void)
233{
234 tcp_unregister_congestion_control(&bictcp);
235}
236
237module_init(bictcp_register);
238module_exit(bictcp_unregister);
239
240MODULE_AUTHOR("Stephen Hemminger");
241MODULE_LICENSE("GPL");
242MODULE_DESCRIPTION("BIC TCP");
243