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83803034 SH |
1 | /* |
2 | * Binary Increase Congestion control for TCP | |
0bc8c7bf SH |
3 | * Home page: |
4 | * http://netsrv.csc.ncsu.edu/twiki/bin/view/Main/BIC | |
83803034 SH |
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: | |
0bc8c7bf | 10 | * http://netsrv.csc.ncsu.edu/export/bitcp.pdf |
83803034 SH |
11 | * |
12 | * Unless BIC is enabled and congestion window is large | |
13 | * this behaves the same as the original Reno. | |
14 | */ | |
15 | ||
83803034 SH |
16 | #include <linux/mm.h> |
17 | #include <linux/module.h> | |
18 | #include <net/tcp.h> | |
19 | ||
83803034 SH |
20 | #define BICTCP_BETA_SCALE 1024 /* Scale factor beta calculation |
21 | * max_cwnd = snd_cwnd * beta | |
22 | */ | |
23 | #define BICTCP_B 4 /* | |
24 | * In binary search, | |
25 | * go to point (max+min)/N | |
26 | */ | |
27 | ||
28 | static int fast_convergence = 1; | |
450b5b18 | 29 | static int max_increment = 16; |
83803034 SH |
30 | static int low_window = 14; |
31 | static int beta = 819; /* = 819/1024 (BICTCP_BETA_SCALE) */ | |
66e1e3b2 | 32 | static int initial_ssthresh; |
83803034 SH |
33 | static int smooth_part = 20; |
34 | ||
35 | module_param(fast_convergence, int, 0644); | |
36 | MODULE_PARM_DESC(fast_convergence, "turn on/off fast convergence"); | |
37 | module_param(max_increment, int, 0644); | |
38 | MODULE_PARM_DESC(max_increment, "Limit on increment allowed during binary search"); | |
39 | module_param(low_window, int, 0644); | |
40 | MODULE_PARM_DESC(low_window, "lower bound on congestion window (for TCP friendliness)"); | |
41 | module_param(beta, int, 0644); | |
42 | MODULE_PARM_DESC(beta, "beta for multiplicative increase"); | |
83803034 SH |
43 | module_param(initial_ssthresh, int, 0644); |
44 | MODULE_PARM_DESC(initial_ssthresh, "initial value of slow start threshold"); | |
45 | module_param(smooth_part, int, 0644); | |
46 | MODULE_PARM_DESC(smooth_part, "log(B/(B*Smin))/log(B/(B-1))+B, # of RTT from Wmax-B to Wmax"); | |
47 | ||
83803034 SH |
48 | /* BIC TCP Parameters */ |
49 | struct bictcp { | |
50 | u32 cnt; /* increase cwnd by 1 after ACKs */ | |
688d1945 | 51 | u32 last_max_cwnd; /* last maximum snd_cwnd */ |
83803034 SH |
52 | u32 loss_cwnd; /* congestion window at last loss */ |
53 | u32 last_cwnd; /* the last snd_cwnd */ | |
54 | u32 last_time; /* time when updated last_cwnd */ | |
83803034 SH |
55 | u32 epoch_start; /* beginning of an epoch */ |
56 | #define ACK_RATIO_SHIFT 4 | |
57 | u32 delayed_ack; /* estimate the ratio of Packets/ACKs << 4 */ | |
58 | }; | |
59 | ||
60 | static inline void bictcp_reset(struct bictcp *ca) | |
61 | { | |
62 | ca->cnt = 0; | |
63 | ca->last_max_cwnd = 0; | |
83803034 SH |
64 | ca->last_cwnd = 0; |
65 | ca->last_time = 0; | |
83803034 SH |
66 | ca->epoch_start = 0; |
67 | ca->delayed_ack = 2 << ACK_RATIO_SHIFT; | |
68 | } | |
69 | ||
6687e988 | 70 | static void bictcp_init(struct sock *sk) |
83803034 | 71 | { |
fc16dcd8 NC |
72 | struct bictcp *ca = inet_csk_ca(sk); |
73 | ||
74 | bictcp_reset(ca); | |
75 | ca->loss_cwnd = 0; | |
76 | ||
83803034 | 77 | if (initial_ssthresh) |
6687e988 | 78 | tcp_sk(sk)->snd_ssthresh = initial_ssthresh; |
83803034 SH |
79 | } |
80 | ||
81 | /* | |
82 | * Compute congestion window to use. | |
83 | */ | |
84 | static 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) /* record the beginning of an epoch */ | |
94 | ca->epoch_start = tcp_time_stamp; | |
95 | ||
96 | /* start off normal */ | |
97 | if (cwnd <= low_window) { | |
98 | ca->cnt = cwnd; | |
99 | return; | |
100 | } | |
101 | ||
102 | /* binary increase */ | |
103 | if (cwnd < ca->last_max_cwnd) { | |
688d1945 | 104 | __u32 dist = (ca->last_max_cwnd - cwnd) |
83803034 SH |
105 | / BICTCP_B; |
106 | ||
107 | if (dist > max_increment) | |
108 | /* linear increase */ | |
109 | ca->cnt = cwnd / max_increment; | |
110 | else if (dist <= 1U) | |
111 | /* binary search increase */ | |
112 | ca->cnt = (cwnd * smooth_part) / BICTCP_B; | |
113 | else | |
114 | /* binary search increase */ | |
115 | ca->cnt = cwnd / dist; | |
116 | } else { | |
117 | /* slow start AMD linear increase */ | |
118 | if (cwnd < ca->last_max_cwnd + BICTCP_B) | |
119 | /* slow start */ | |
120 | ca->cnt = (cwnd * smooth_part) / BICTCP_B; | |
121 | else if (cwnd < ca->last_max_cwnd + max_increment*(BICTCP_B-1)) | |
122 | /* slow start */ | |
123 | ca->cnt = (cwnd * (BICTCP_B-1)) | |
42a39450 | 124 | / (cwnd - ca->last_max_cwnd); |
83803034 SH |
125 | else |
126 | /* linear increase */ | |
127 | ca->cnt = cwnd / max_increment; | |
128 | } | |
129 | ||
130 | /* if in slow start or link utilization is very low */ | |
fc16dcd8 | 131 | if (ca->last_max_cwnd == 0) { |
83803034 SH |
132 | if (ca->cnt > 20) /* increase cwnd 5% per RTT */ |
133 | ca->cnt = 20; | |
134 | } | |
135 | ||
136 | ca->cnt = (ca->cnt << ACK_RATIO_SHIFT) / ca->delayed_ack; | |
137 | if (ca->cnt == 0) /* cannot be zero */ | |
138 | ca->cnt = 1; | |
139 | } | |
140 | ||
24901551 | 141 | static void bictcp_cong_avoid(struct sock *sk, u32 ack, u32 acked) |
83803034 | 142 | { |
6687e988 ACM |
143 | struct tcp_sock *tp = tcp_sk(sk); |
144 | struct bictcp *ca = inet_csk_ca(sk); | |
83803034 | 145 | |
24901551 | 146 | if (!tcp_is_cwnd_limited(sk)) |
83803034 SH |
147 | return; |
148 | ||
071d5080 | 149 | if (tcp_in_slow_start(tp)) |
9f9843a7 | 150 | tcp_slow_start(tp, acked); |
7faffa1c | 151 | else { |
83803034 | 152 | bictcp_update(ca, tp->snd_cwnd); |
e73ebb08 | 153 | tcp_cong_avoid_ai(tp, ca->cnt, 1); |
83803034 | 154 | } |
83803034 SH |
155 | } |
156 | ||
157 | /* | |
158 | * behave like Reno until low_window is reached, | |
159 | * then increase congestion window slowly | |
160 | */ | |
6687e988 | 161 | static u32 bictcp_recalc_ssthresh(struct sock *sk) |
83803034 | 162 | { |
6687e988 ACM |
163 | const struct tcp_sock *tp = tcp_sk(sk); |
164 | struct bictcp *ca = inet_csk_ca(sk); | |
83803034 SH |
165 | |
166 | ca->epoch_start = 0; /* end of epoch */ | |
167 | ||
83803034 SH |
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); | |
172 | else | |
173 | ca->last_max_cwnd = tp->snd_cwnd; | |
174 | ||
175 | ca->loss_cwnd = tp->snd_cwnd; | |
176 | ||
83803034 SH |
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 | ||
6687e988 | 183 | static u32 bictcp_undo_cwnd(struct sock *sk) |
83803034 | 184 | { |
6687e988 ACM |
185 | const struct tcp_sock *tp = tcp_sk(sk); |
186 | const struct bictcp *ca = inet_csk_ca(sk); | |
688d1945 | 187 | |
fc16dcd8 | 188 | return max(tp->snd_cwnd, ca->loss_cwnd); |
83803034 SH |
189 | } |
190 | ||
6687e988 | 191 | static void bictcp_state(struct sock *sk, u8 new_state) |
83803034 SH |
192 | { |
193 | if (new_state == TCP_CA_Loss) | |
6687e988 | 194 | bictcp_reset(inet_csk_ca(sk)); |
83803034 SH |
195 | } |
196 | ||
05d05450 | 197 | /* Track delayed acknowledgment ratio using sliding window |
83803034 SH |
198 | * ratio = (15*ratio + sample) / 16 |
199 | */ | |
30cfd0ba | 200 | static void bictcp_acked(struct sock *sk, u32 cnt, s32 rtt) |
83803034 | 201 | { |
6687e988 ACM |
202 | const struct inet_connection_sock *icsk = inet_csk(sk); |
203 | ||
35e86941 | 204 | if (icsk->icsk_ca_state == TCP_CA_Open) { |
6687e988 | 205 | struct bictcp *ca = inet_csk_ca(sk); |
688d1945 | 206 | |
83803034 SH |
207 | cnt -= ca->delayed_ack >> ACK_RATIO_SHIFT; |
208 | ca->delayed_ack += cnt; | |
209 | } | |
210 | } | |
211 | ||
a252bebe | 212 | static struct tcp_congestion_ops bictcp __read_mostly = { |
83803034 SH |
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, | |
83803034 SH |
218 | .pkts_acked = bictcp_acked, |
219 | .owner = THIS_MODULE, | |
220 | .name = "bic", | |
221 | }; | |
222 | ||
223 | static int __init bictcp_register(void) | |
224 | { | |
65e3d726 | 225 | BUILD_BUG_ON(sizeof(struct bictcp) > ICSK_CA_PRIV_SIZE); |
83803034 SH |
226 | return tcp_register_congestion_control(&bictcp); |
227 | } | |
228 | ||
229 | static void __exit bictcp_unregister(void) | |
230 | { | |
231 | tcp_unregister_congestion_control(&bictcp); | |
232 | } | |
233 | ||
234 | module_init(bictcp_register); | |
235 | module_exit(bictcp_unregister); | |
236 | ||
237 | MODULE_AUTHOR("Stephen Hemminger"); | |
238 | MODULE_LICENSE("GPL"); | |
239 | MODULE_DESCRIPTION("BIC TCP"); |