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-rw-r--r--net/ipv4/tcp_bic.c331
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diff --git a/net/ipv4/tcp_bic.c b/net/ipv4/tcp_bic.c
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1/*
2 * Binary Increase Congestion control for TCP
3 *
4 * This is from the implementation of BICTCP in
5 * Lison-Xu, Kahaled Harfoush, and Injong Rhee.
6 * "Binary Increase Congestion Control for Fast, Long Distance
7 * Networks" in InfoComm 2004
8 * Available from:
9 * http://www.csc.ncsu.edu/faculty/rhee/export/bitcp.pdf
10 *
11 * Unless BIC is enabled and congestion window is large
12 * this behaves the same as the original Reno.
13 */
14
15#include <linux/config.h>
16#include <linux/mm.h>
17#include <linux/module.h>
18#include <net/tcp.h>
19
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 = 32;
31static int low_window = 14;
32static int beta = 819; /* = 819/1024 (BICTCP_BETA_SCALE) */
33static int low_utilization_threshold = 153;
34static int low_utilization_period = 2;
35static int initial_ssthresh = 100;
36static int smooth_part = 20;
37
38module_param(fast_convergence, int, 0644);
39MODULE_PARM_DESC(fast_convergence, "turn on/off fast convergence");
40module_param(max_increment, int, 0644);
41MODULE_PARM_DESC(max_increment, "Limit on increment allowed during binary search");
42module_param(low_window, int, 0644);
43MODULE_PARM_DESC(low_window, "lower bound on congestion window (for TCP friendliness)");
44module_param(beta, int, 0644);
45MODULE_PARM_DESC(beta, "beta for multiplicative increase");
46module_param(low_utilization_threshold, int, 0644);
47MODULE_PARM_DESC(low_utilization_threshold, "percent (scaled by 1024) for low utilization mode");
48module_param(low_utilization_period, int, 0644);
49MODULE_PARM_DESC(low_utilization_period, "if average delay exceeds then goto to low utilization mode (seconds)");
50module_param(initial_ssthresh, int, 0644);
51MODULE_PARM_DESC(initial_ssthresh, "initial value of slow start threshold");
52module_param(smooth_part, int, 0644);
53MODULE_PARM_DESC(smooth_part, "log(B/(B*Smin))/log(B/(B-1))+B, # of RTT from Wmax-B to Wmax");
54
55
56/* BIC TCP Parameters */
57struct bictcp {
58 u32 cnt; /* increase cwnd by 1 after ACKs */
59 u32 last_max_cwnd; /* last maximum snd_cwnd */
60 u32 loss_cwnd; /* congestion window at last loss */
61 u32 last_cwnd; /* the last snd_cwnd */
62 u32 last_time; /* time when updated last_cwnd */
63 u32 delay_min; /* min delay */
64 u32 delay_max; /* max delay */
65 u32 last_delay;
66 u8 low_utilization;/* 0: high; 1: low */
67 u32 low_utilization_start; /* starting time of low utilization detection*/
68 u32 epoch_start; /* beginning of an epoch */
69#define ACK_RATIO_SHIFT 4
70 u32 delayed_ack; /* estimate the ratio of Packets/ACKs << 4 */
71};
72
73static inline void bictcp_reset(struct bictcp *ca)
74{
75 ca->cnt = 0;
76 ca->last_max_cwnd = 0;
77 ca->loss_cwnd = 0;
78 ca->last_cwnd = 0;
79 ca->last_time = 0;
80 ca->delay_min = 0;
81 ca->delay_max = 0;
82 ca->last_delay = 0;
83 ca->low_utilization = 0;
84 ca->low_utilization_start = 0;
85 ca->epoch_start = 0;
86 ca->delayed_ack = 2 << ACK_RATIO_SHIFT;
87}
88
89static void bictcp_init(struct tcp_sock *tp)
90{
91 bictcp_reset(tcp_ca(tp));
92 if (initial_ssthresh)
93 tp->snd_ssthresh = initial_ssthresh;
94}
95
96/*
97 * Compute congestion window to use.
98 */
99static inline void bictcp_update(struct bictcp *ca, u32 cwnd)
100{
101 if (ca->last_cwnd == cwnd &&
102 (s32)(tcp_time_stamp - ca->last_time) <= HZ / 32)
103 return;
104
105 ca->last_cwnd = cwnd;
106 ca->last_time = tcp_time_stamp;
107
108 if (ca->epoch_start == 0) /* record the beginning of an epoch */
109 ca->epoch_start = tcp_time_stamp;
110
111 /* start off normal */
112 if (cwnd <= low_window) {
113 ca->cnt = cwnd;
114 return;
115 }
116
117 /* binary increase */
118 if (cwnd < ca->last_max_cwnd) {
119 __u32 dist = (ca->last_max_cwnd - cwnd)
120 / BICTCP_B;
121
122 if (dist > max_increment)
123 /* linear increase */
124 ca->cnt = cwnd / max_increment;
125 else if (dist <= 1U)
126 /* binary search increase */
127 ca->cnt = (cwnd * smooth_part) / BICTCP_B;
128 else
129 /* binary search increase */
130 ca->cnt = cwnd / dist;
131 } else {
132 /* slow start AMD linear increase */
133 if (cwnd < ca->last_max_cwnd + BICTCP_B)
134 /* slow start */
135 ca->cnt = (cwnd * smooth_part) / BICTCP_B;
136 else if (cwnd < ca->last_max_cwnd + max_increment*(BICTCP_B-1))
137 /* slow start */
138 ca->cnt = (cwnd * (BICTCP_B-1))
139 / cwnd-ca->last_max_cwnd;
140 else
141 /* linear increase */
142 ca->cnt = cwnd / max_increment;
143 }
144
145 /* if in slow start or link utilization is very low */
146 if ( ca->loss_cwnd == 0 ||
147 (cwnd > ca->loss_cwnd && ca->low_utilization)) {
148 if (ca->cnt > 20) /* increase cwnd 5% per RTT */
149 ca->cnt = 20;
150 }
151
152 ca->cnt = (ca->cnt << ACK_RATIO_SHIFT) / ca->delayed_ack;
153 if (ca->cnt == 0) /* cannot be zero */
154 ca->cnt = 1;
155}
156
157
158/* Detect low utilization in congestion avoidance */
159static inline void bictcp_low_utilization(struct tcp_sock *tp, int flag)
160{
161 struct bictcp *ca = tcp_ca(tp);
162 u32 dist, delay;
163
164 /* No time stamp */
165 if (!(tp->rx_opt.saw_tstamp && tp->rx_opt.rcv_tsecr) ||
166 /* Discard delay samples right after fast recovery */
167 tcp_time_stamp < ca->epoch_start + HZ ||
168 /* this delay samples may not be accurate */
169 flag == 0) {
170 ca->last_delay = 0;
171 goto notlow;
172 }
173
174 delay = ca->last_delay<<3; /* use the same scale as tp->srtt*/
175 ca->last_delay = tcp_time_stamp - tp->rx_opt.rcv_tsecr;
176 if (delay == 0) /* no previous delay sample */
177 goto notlow;
178
179 /* first time call or link delay decreases */
180 if (ca->delay_min == 0 || ca->delay_min > delay) {
181 ca->delay_min = ca->delay_max = delay;
182 goto notlow;
183 }
184
185 if (ca->delay_max < delay)
186 ca->delay_max = delay;
187
188 /* utilization is low, if avg delay < dist*threshold
189 for checking_period time */
190 dist = ca->delay_max - ca->delay_min;
191 if (dist <= ca->delay_min>>6 ||
192 tp->srtt - ca->delay_min >= (dist*low_utilization_threshold)>>10)
193 goto notlow;
194
195 if (ca->low_utilization_start == 0) {
196 ca->low_utilization = 0;
197 ca->low_utilization_start = tcp_time_stamp;
198 } else if ((s32)(tcp_time_stamp - ca->low_utilization_start)
199 > low_utilization_period*HZ) {
200 ca->low_utilization = 1;
201 }
202
203 return;
204
205 notlow:
206 ca->low_utilization = 0;
207 ca->low_utilization_start = 0;
208
209}
210
211static void bictcp_cong_avoid(struct tcp_sock *tp, u32 ack,
212 u32 seq_rtt, u32 in_flight, int data_acked)
213{
214 struct bictcp *ca = tcp_ca(tp);
215
216 bictcp_low_utilization(tp, data_acked);
217
218 if (in_flight < tp->snd_cwnd)
219 return;
220
221 if (tp->snd_cwnd <= tp->snd_ssthresh) {
222 /* In "safe" area, increase. */
223 if (tp->snd_cwnd < tp->snd_cwnd_clamp)
224 tp->snd_cwnd++;
225 } else {
226 bictcp_update(ca, tp->snd_cwnd);
227
228 /* In dangerous area, increase slowly.
229 * In theory this is tp->snd_cwnd += 1 / tp->snd_cwnd
230 */
231 if (tp->snd_cwnd_cnt >= ca->cnt) {
232 if (tp->snd_cwnd < tp->snd_cwnd_clamp)
233 tp->snd_cwnd++;
234 tp->snd_cwnd_cnt = 0;
235 } else
236 tp->snd_cwnd_cnt++;
237 }
238
239}
240
241/*
242 * behave like Reno until low_window is reached,
243 * then increase congestion window slowly
244 */
245static u32 bictcp_recalc_ssthresh(struct tcp_sock *tp)
246{
247 struct bictcp *ca = tcp_ca(tp);
248
249 ca->epoch_start = 0; /* end of epoch */
250
251 /* in case of wrong delay_max*/
252 if (ca->delay_min > 0 && ca->delay_max > ca->delay_min)
253 ca->delay_max = ca->delay_min
254 + ((ca->delay_max - ca->delay_min)* 90) / 100;
255
256 /* Wmax and fast convergence */
257 if (tp->snd_cwnd < ca->last_max_cwnd && fast_convergence)
258 ca->last_max_cwnd = (tp->snd_cwnd * (BICTCP_BETA_SCALE + beta))
259 / (2 * BICTCP_BETA_SCALE);
260 else
261 ca->last_max_cwnd = tp->snd_cwnd;
262
263 ca->loss_cwnd = tp->snd_cwnd;
264
265
266 if (tp->snd_cwnd <= low_window)
267 return max(tp->snd_cwnd >> 1U, 2U);
268 else
269 return max((tp->snd_cwnd * beta) / BICTCP_BETA_SCALE, 2U);
270}
271
272static u32 bictcp_undo_cwnd(struct tcp_sock *tp)
273{
274 struct bictcp *ca = tcp_ca(tp);
275
276 return max(tp->snd_cwnd, ca->last_max_cwnd);
277}
278
279static u32 bictcp_min_cwnd(struct tcp_sock *tp)
280{
281 return tp->snd_ssthresh;
282}
283
284static void bictcp_state(struct tcp_sock *tp, u8 new_state)
285{
286 if (new_state == TCP_CA_Loss)
287 bictcp_reset(tcp_ca(tp));
288}
289
290/* Track delayed acknowledgement ratio using sliding window
291 * ratio = (15*ratio + sample) / 16
292 */
293static void bictcp_acked(struct tcp_sock *tp, u32 cnt)
294{
295 if (cnt > 0 && tp->ca_state == TCP_CA_Open) {
296 struct bictcp *ca = tcp_ca(tp);
297 cnt -= ca->delayed_ack >> ACK_RATIO_SHIFT;
298 ca->delayed_ack += cnt;
299 }
300}
301
302
303static struct tcp_congestion_ops bictcp = {
304 .init = bictcp_init,
305 .ssthresh = bictcp_recalc_ssthresh,
306 .cong_avoid = bictcp_cong_avoid,
307 .set_state = bictcp_state,
308 .undo_cwnd = bictcp_undo_cwnd,
309 .min_cwnd = bictcp_min_cwnd,
310 .pkts_acked = bictcp_acked,
311 .owner = THIS_MODULE,
312 .name = "bic",
313};
314
315static int __init bictcp_register(void)
316{
317 BUG_ON(sizeof(struct bictcp) > TCP_CA_PRIV_SIZE);
318 return tcp_register_congestion_control(&bictcp);
319}
320
321static void __exit bictcp_unregister(void)
322{
323 tcp_unregister_congestion_control(&bictcp);
324}
325
326module_init(bictcp_register);
327module_exit(bictcp_unregister);
328
329MODULE_AUTHOR("Stephen Hemminger");
330MODULE_LICENSE("GPL");
331MODULE_DESCRIPTION("BIC TCP");