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