Commit | Line | Data |
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83803034 SH |
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 | ||
29 | static int fast_convergence = 1; | |
30 | static int max_increment = 32; | |
31 | static int low_window = 14; | |
32 | static int beta = 819; /* = 819/1024 (BICTCP_BETA_SCALE) */ | |
33 | static int low_utilization_threshold = 153; | |
34 | static int low_utilization_period = 2; | |
35 | static int initial_ssthresh = 100; | |
36 | static int smooth_part = 20; | |
37 | ||
38 | module_param(fast_convergence, int, 0644); | |
39 | MODULE_PARM_DESC(fast_convergence, "turn on/off fast convergence"); | |
40 | module_param(max_increment, int, 0644); | |
41 | MODULE_PARM_DESC(max_increment, "Limit on increment allowed during binary search"); | |
42 | module_param(low_window, int, 0644); | |
43 | MODULE_PARM_DESC(low_window, "lower bound on congestion window (for TCP friendliness)"); | |
44 | module_param(beta, int, 0644); | |
45 | MODULE_PARM_DESC(beta, "beta for multiplicative increase"); | |
46 | module_param(low_utilization_threshold, int, 0644); | |
47 | MODULE_PARM_DESC(low_utilization_threshold, "percent (scaled by 1024) for low utilization mode"); | |
48 | module_param(low_utilization_period, int, 0644); | |
49 | MODULE_PARM_DESC(low_utilization_period, "if average delay exceeds then goto to low utilization mode (seconds)"); | |
50 | module_param(initial_ssthresh, int, 0644); | |
51 | MODULE_PARM_DESC(initial_ssthresh, "initial value of slow start threshold"); | |
52 | module_param(smooth_part, int, 0644); | |
53 | MODULE_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 */ | |
57 | struct 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 | ||
73 | static 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 | ||
89 | static 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 | */ | |
99 | static 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 */ | |
159 | static 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 | ||
211 | static 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 | */ | |
245 | static 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 | ||
272 | static 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 | ||
279 | static u32 bictcp_min_cwnd(struct tcp_sock *tp) | |
280 | { | |
281 | return tp->snd_ssthresh; | |
282 | } | |
283 | ||
284 | static 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 | */ | |
293 | static 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 | ||
303 | static 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 | ||
315 | static 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 | ||
321 | static void __exit bictcp_unregister(void) | |
322 | { | |
323 | tcp_unregister_congestion_control(&bictcp); | |
324 | } | |
325 | ||
326 | module_init(bictcp_register); | |
327 | module_exit(bictcp_unregister); | |
328 | ||
329 | MODULE_AUTHOR("Stephen Hemminger"); | |
330 | MODULE_LICENSE("GPL"); | |
331 | MODULE_DESCRIPTION("BIC TCP"); |