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1// SPDX-License-Identifier: GPL-2.0-only
2/*
3 * Binary Increase Congestion control for TCP
4 * Home page:
5 * http://netsrv.csc.ncsu.edu/twiki/bin/view/Main/BIC
6 * This is from the implementation of BICTCP in
7 * Lison-Xu, Kahaled Harfoush, and Injong Rhee.
8 * "Binary Increase Congestion Control for Fast, Long Distance
9 * Networks" in InfoComm 2004
10 * Available from:
11 * http://netsrv.csc.ncsu.edu/export/bitcp.pdf
12 *
13 * Unless BIC is enabled and congestion window is large
14 * this behaves the same as the original Reno.
15 */
16
17#include <linux/mm.h>
18#include <linux/module.h>
19#include <net/tcp.h>
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
29static int fast_convergence = 1;
30static int max_increment = 16;
31static int low_window = 14;
32static int beta = 819; /* = 819/1024 (BICTCP_BETA_SCALE) */
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/* BIC TCP Parameters */
50struct bictcp {
51 u32 cnt; /* increase cwnd by 1 after ACKs */
52 u32 last_max_cwnd; /* last maximum snd_cwnd */
53 u32 last_cwnd; /* the last snd_cwnd */
54 u32 last_time; /* time when updated last_cwnd */
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
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
76 if (initial_ssthresh)
77 tcp_sk(sk)->snd_ssthresh = initial_ssthresh;
78}
79
80/*
81 * Compute congestion window to use.
82 */
83static inline void bictcp_update(struct bictcp *ca, u32 cwnd)
84{
85 if (ca->last_cwnd == cwnd &&
86 (s32)(tcp_jiffies32 - ca->last_time) <= HZ / 32)
87 return;
88
89 ca->last_cwnd = cwnd;
90 ca->last_time = tcp_jiffies32;
91
92 if (ca->epoch_start == 0) /* record the beginning of an epoch */
93 ca->epoch_start = tcp_jiffies32;
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->last_max_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
140static void bictcp_cong_avoid(struct sock *sk, u32 ack, u32 acked)
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))
146 return;
147
148 if (tcp_in_slow_start(tp)) {
149 acked = tcp_slow_start(tp, acked);
150 if (!acked)
151 return;
152 }
153 bictcp_update(ca, tcp_snd_cwnd(tp));
154 tcp_cong_avoid_ai(tp, ca->cnt, acked);
155}
156
157/*
158 * behave like Reno until low_window is reached,
159 * then increase congestion window slowly
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; /* end of epoch */
167
168 /* Wmax and fast convergence */
169 if (tcp_snd_cwnd(tp) < ca->last_max_cwnd && fast_convergence)
170 ca->last_max_cwnd = (tcp_snd_cwnd(tp) * (BICTCP_BETA_SCALE + beta))
171 / (2 * BICTCP_BETA_SCALE);
172 else
173 ca->last_max_cwnd = tcp_snd_cwnd(tp);
174
175 if (tcp_snd_cwnd(tp) <= low_window)
176 return max(tcp_snd_cwnd(tp) >> 1U, 2U);
177 else
178 return max((tcp_snd_cwnd(tp) * beta) / BICTCP_BETA_SCALE, 2U);
179}
180
181static void bictcp_state(struct sock *sk, u8 new_state)
182{
183 if (new_state == TCP_CA_Loss)
184 bictcp_reset(inet_csk_ca(sk));
185}
186
187/* Track delayed acknowledgment ratio using sliding window
188 * ratio = (15*ratio + sample) / 16
189 */
190static void bictcp_acked(struct sock *sk, const struct ack_sample *sample)
191{
192 const struct inet_connection_sock *icsk = inet_csk(sk);
193
194 if (icsk->icsk_ca_state == TCP_CA_Open) {
195 struct bictcp *ca = inet_csk_ca(sk);
196
197 ca->delayed_ack += sample->pkts_acked -
198 (ca->delayed_ack >> ACK_RATIO_SHIFT);
199 }
200}
201
202static struct tcp_congestion_ops bictcp __read_mostly = {
203 .init = bictcp_init,
204 .ssthresh = bictcp_recalc_ssthresh,
205 .cong_avoid = bictcp_cong_avoid,
206 .set_state = bictcp_state,
207 .undo_cwnd = tcp_reno_undo_cwnd,
208 .pkts_acked = bictcp_acked,
209 .owner = THIS_MODULE,
210 .name = "bic",
211};
212
213static int __init bictcp_register(void)
214{
215 BUILD_BUG_ON(sizeof(struct bictcp) > ICSK_CA_PRIV_SIZE);
216 return tcp_register_congestion_control(&bictcp);
217}
218
219static void __exit bictcp_unregister(void)
220{
221 tcp_unregister_congestion_control(&bictcp);
222}
223
224module_init(bictcp_register);
225module_exit(bictcp_unregister);
226
227MODULE_AUTHOR("Stephen Hemminger");
228MODULE_LICENSE("GPL");
229MODULE_DESCRIPTION("BIC TCP");
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#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
28static int fast_convergence = 1;
29static int max_increment = 16;
30static int low_window = 14;
31static int beta = 819; /* = 819/1024 (BICTCP_BETA_SCALE) */
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/* BIC TCP Parameters */
49struct bictcp {
50 u32 cnt; /* increase cwnd by 1 after ACKs */
51 u32 last_max_cwnd; /* last maximum snd_cwnd */
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 */
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
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 * Compute congestion window to use.
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) /* 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) {
104 __u32 dist = (ca->last_max_cwnd - cwnd)
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))
124 / (cwnd - ca->last_max_cwnd);
125 else
126 /* linear increase */
127 ca->cnt = cwnd / max_increment;
128 }
129
130 /* if in slow start or link utilization is very low */
131 if (ca->last_max_cwnd == 0) {
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
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
157/*
158 * behave like Reno until low_window is reached,
159 * then increase congestion window slowly
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; /* end of epoch */
167
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
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/* Track delayed acknowledgment ratio using sliding window
198 * ratio = (15*ratio + sample) / 16
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");