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09c434b8 | 1 | // SPDX-License-Identifier: GPL-2.0-only |
c462238d SH |
2 | /* |
3 | * TCP Illinois congestion control. | |
4 | * Home page: | |
5 | * http://www.ews.uiuc.edu/~shaoliu/tcpillinois/index.html | |
6 | * | |
7 | * The algorithm is described in: | |
8 | * "TCP-Illinois: A Loss and Delay-Based Congestion Control Algorithm | |
9 | * for High-Speed Networks" | |
ecc83275 | 10 | * http://tamerbasar.csl.illinois.edu/LiuBasarSrikantPerfEvalArtJun2008.pdf |
c462238d SH |
11 | * |
12 | * Implemented from description in paper and ns-2 simulation. | |
13 | * Copyright (C) 2007 Stephen Hemminger <shemminger@linux-foundation.org> | |
14 | */ | |
15 | ||
16 | #include <linux/module.h> | |
17 | #include <linux/skbuff.h> | |
18 | #include <linux/inet_diag.h> | |
19 | #include <asm/div64.h> | |
20 | #include <net/tcp.h> | |
21 | ||
22 | #define ALPHA_SHIFT 7 | |
23 | #define ALPHA_SCALE (1u<<ALPHA_SHIFT) | |
24 | #define ALPHA_MIN ((3*ALPHA_SCALE)/10) /* ~0.3 */ | |
25 | #define ALPHA_MAX (10*ALPHA_SCALE) /* 10.0 */ | |
26 | #define ALPHA_BASE ALPHA_SCALE /* 1.0 */ | |
65d1b4a7 | 27 | #define RTT_MAX (U32_MAX / ALPHA_MAX) /* 3.3 secs */ |
c462238d SH |
28 | |
29 | #define BETA_SHIFT 6 | |
30 | #define BETA_SCALE (1u<<BETA_SHIFT) | |
65d1b4a7 SH |
31 | #define BETA_MIN (BETA_SCALE/8) /* 0.125 */ |
32 | #define BETA_MAX (BETA_SCALE/2) /* 0.5 */ | |
33 | #define BETA_BASE BETA_MAX | |
c462238d SH |
34 | |
35 | static int win_thresh __read_mostly = 15; | |
65d1b4a7 | 36 | module_param(win_thresh, int, 0); |
c462238d SH |
37 | MODULE_PARM_DESC(win_thresh, "Window threshold for starting adaptive sizing"); |
38 | ||
65d1b4a7 SH |
39 | static int theta __read_mostly = 5; |
40 | module_param(theta, int, 0); | |
41 | MODULE_PARM_DESC(theta, "# of fast RTT's before full growth"); | |
c462238d SH |
42 | |
43 | /* TCP Illinois Parameters */ | |
65d1b4a7 SH |
44 | struct illinois { |
45 | u64 sum_rtt; /* sum of rtt's measured within last rtt */ | |
46 | u16 cnt_rtt; /* # of rtts measured within last rtt */ | |
47 | u32 base_rtt; /* min of all rtt in usec */ | |
48 | u32 max_rtt; /* max of all rtt in usec */ | |
49 | u32 end_seq; /* right edge of current RTT */ | |
50 | u32 alpha; /* Additive increase */ | |
51 | u32 beta; /* Muliplicative decrease */ | |
52 | u16 acked; /* # packets acked by current ACK */ | |
53 | u8 rtt_above; /* average rtt has gone above threshold */ | |
54 | u8 rtt_low; /* # of rtts measurements below threshold */ | |
c462238d SH |
55 | }; |
56 | ||
65d1b4a7 SH |
57 | static void rtt_reset(struct sock *sk) |
58 | { | |
59 | struct tcp_sock *tp = tcp_sk(sk); | |
60 | struct illinois *ca = inet_csk_ca(sk); | |
61 | ||
62 | ca->end_seq = tp->snd_nxt; | |
63 | ca->cnt_rtt = 0; | |
64 | ca->sum_rtt = 0; | |
65 | ||
66 | /* TODO: age max_rtt? */ | |
67 | } | |
68 | ||
c462238d SH |
69 | static void tcp_illinois_init(struct sock *sk) |
70 | { | |
65d1b4a7 SH |
71 | struct illinois *ca = inet_csk_ca(sk); |
72 | ||
73 | ca->alpha = ALPHA_MAX; | |
74 | ca->beta = BETA_BASE; | |
75 | ca->base_rtt = 0x7fffffff; | |
76 | ca->max_rtt = 0; | |
77 | ||
78 | ca->acked = 0; | |
79 | ca->rtt_low = 0; | |
80 | ca->rtt_above = 0; | |
c462238d | 81 | |
65d1b4a7 | 82 | rtt_reset(sk); |
c462238d SH |
83 | } |
84 | ||
65d1b4a7 | 85 | /* Measure RTT for each ack. */ |
756ee172 | 86 | static void tcp_illinois_acked(struct sock *sk, const struct ack_sample *sample) |
c462238d | 87 | { |
65d1b4a7 | 88 | struct illinois *ca = inet_csk_ca(sk); |
756ee172 | 89 | s32 rtt_us = sample->rtt_us; |
164891aa | 90 | |
756ee172 | 91 | ca->acked = sample->pkts_acked; |
164891aa | 92 | |
30cfd0ba | 93 | /* dup ack, no rtt sample */ |
756ee172 | 94 | if (rtt_us < 0) |
b9ce204f IJ |
95 | return; |
96 | ||
65d1b4a7 | 97 | /* ignore bogus values, this prevents wraparound in alpha math */ |
756ee172 LB |
98 | if (rtt_us > RTT_MAX) |
99 | rtt_us = RTT_MAX; | |
c462238d | 100 | |
65d1b4a7 | 101 | /* keep track of minimum RTT seen so far */ |
756ee172 LB |
102 | if (ca->base_rtt > rtt_us) |
103 | ca->base_rtt = rtt_us; | |
65d1b4a7 SH |
104 | |
105 | /* and max */ | |
756ee172 LB |
106 | if (ca->max_rtt < rtt_us) |
107 | ca->max_rtt = rtt_us; | |
c462238d | 108 | |
65d1b4a7 | 109 | ++ca->cnt_rtt; |
756ee172 | 110 | ca->sum_rtt += rtt_us; |
c462238d SH |
111 | } |
112 | ||
65d1b4a7 SH |
113 | /* Maximum queuing delay */ |
114 | static inline u32 max_delay(const struct illinois *ca) | |
c462238d | 115 | { |
65d1b4a7 SH |
116 | return ca->max_rtt - ca->base_rtt; |
117 | } | |
c462238d | 118 | |
65d1b4a7 SH |
119 | /* Average queuing delay */ |
120 | static inline u32 avg_delay(const struct illinois *ca) | |
121 | { | |
122 | u64 t = ca->sum_rtt; | |
c462238d | 123 | |
65d1b4a7 SH |
124 | do_div(t, ca->cnt_rtt); |
125 | return t - ca->base_rtt; | |
c462238d SH |
126 | } |
127 | ||
128 | /* | |
129 | * Compute value of alpha used for additive increase. | |
130 | * If small window then use 1.0, equivalent to Reno. | |
131 | * | |
132 | * For larger windows, adjust based on average delay. | |
133 | * A. If average delay is at minimum (we are uncongested), | |
134 | * then use large alpha (10.0) to increase faster. | |
135 | * B. If average delay is at maximum (getting congested) | |
65d1b4a7 | 136 | * then use small alpha (0.3) |
c462238d SH |
137 | * |
138 | * The result is a convex window growth curve. | |
139 | */ | |
65d1b4a7 | 140 | static u32 alpha(struct illinois *ca, u32 da, u32 dm) |
c462238d | 141 | { |
65d1b4a7 | 142 | u32 d1 = dm / 100; /* Low threshold */ |
c462238d | 143 | |
c462238d | 144 | if (da <= d1) { |
65d1b4a7 SH |
145 | /* If never got out of low delay zone, then use max */ |
146 | if (!ca->rtt_above) | |
c462238d | 147 | return ALPHA_MAX; |
65d1b4a7 SH |
148 | |
149 | /* Wait for 5 good RTT's before allowing alpha to go alpha max. | |
150 | * This prevents one good RTT from causing sudden window increase. | |
151 | */ | |
152 | if (++ca->rtt_low < theta) | |
153 | return ca->alpha; | |
154 | ||
155 | ca->rtt_low = 0; | |
156 | ca->rtt_above = 0; | |
157 | return ALPHA_MAX; | |
c462238d SH |
158 | } |
159 | ||
65d1b4a7 | 160 | ca->rtt_above = 1; |
c462238d SH |
161 | |
162 | /* | |
163 | * Based on: | |
164 | * | |
165 | * (dm - d1) amin amax | |
166 | * k1 = ------------------- | |
167 | * amax - amin | |
168 | * | |
169 | * (dm - d1) amin | |
170 | * k2 = ---------------- - d1 | |
171 | * amax - amin | |
172 | * | |
173 | * k1 | |
174 | * alpha = ---------- | |
175 | * k2 + da | |
176 | */ | |
177 | ||
178 | dm -= d1; | |
179 | da -= d1; | |
65d1b4a7 SH |
180 | return (dm * ALPHA_MAX) / |
181 | (dm + (da * (ALPHA_MAX - ALPHA_MIN)) / ALPHA_MIN); | |
c462238d SH |
182 | } |
183 | ||
184 | /* | |
185 | * Beta used for multiplicative decrease. | |
186 | * For small window sizes returns same value as Reno (0.5) | |
187 | * | |
188 | * If delay is small (10% of max) then beta = 1/8 | |
189 | * If delay is up to 80% of max then beta = 1/2 | |
190 | * In between is a linear function | |
191 | */ | |
65d1b4a7 | 192 | static u32 beta(u32 da, u32 dm) |
c462238d | 193 | { |
c462238d SH |
194 | u32 d2, d3; |
195 | ||
c462238d SH |
196 | d2 = dm / 10; |
197 | if (da <= d2) | |
198 | return BETA_MIN; | |
65d1b4a7 | 199 | |
c462238d SH |
200 | d3 = (8 * dm) / 10; |
201 | if (da >= d3 || d3 <= d2) | |
202 | return BETA_MAX; | |
203 | ||
204 | /* | |
205 | * Based on: | |
206 | * | |
207 | * bmin d3 - bmax d2 | |
208 | * k3 = ------------------- | |
209 | * d3 - d2 | |
210 | * | |
211 | * bmax - bmin | |
212 | * k4 = ------------- | |
213 | * d3 - d2 | |
214 | * | |
215 | * b = k3 + k4 da | |
216 | */ | |
217 | return (BETA_MIN * d3 - BETA_MAX * d2 + (BETA_MAX - BETA_MIN) * da) | |
218 | / (d3 - d2); | |
219 | } | |
220 | ||
65d1b4a7 SH |
221 | /* Update alpha and beta values once per RTT */ |
222 | static void update_params(struct sock *sk) | |
223 | { | |
224 | struct tcp_sock *tp = tcp_sk(sk); | |
225 | struct illinois *ca = inet_csk_ca(sk); | |
226 | ||
40570375 | 227 | if (tcp_snd_cwnd(tp) < win_thresh) { |
65d1b4a7 SH |
228 | ca->alpha = ALPHA_BASE; |
229 | ca->beta = BETA_BASE; | |
230 | } else if (ca->cnt_rtt > 0) { | |
231 | u32 dm = max_delay(ca); | |
232 | u32 da = avg_delay(ca); | |
233 | ||
234 | ca->alpha = alpha(ca, da, dm); | |
235 | ca->beta = beta(da, dm); | |
236 | } | |
237 | ||
238 | rtt_reset(sk); | |
239 | } | |
240 | ||
241 | /* | |
242 | * In case of loss, reset to default values | |
243 | */ | |
244 | static void tcp_illinois_state(struct sock *sk, u8 new_state) | |
245 | { | |
246 | struct illinois *ca = inet_csk_ca(sk); | |
247 | ||
248 | if (new_state == TCP_CA_Loss) { | |
249 | ca->alpha = ALPHA_BASE; | |
250 | ca->beta = BETA_BASE; | |
251 | ca->rtt_low = 0; | |
252 | ca->rtt_above = 0; | |
253 | rtt_reset(sk); | |
254 | } | |
255 | } | |
256 | ||
257 | /* | |
258 | * Increase window in response to successful acknowledgment. | |
259 | */ | |
24901551 | 260 | static void tcp_illinois_cong_avoid(struct sock *sk, u32 ack, u32 acked) |
65d1b4a7 SH |
261 | { |
262 | struct tcp_sock *tp = tcp_sk(sk); | |
263 | struct illinois *ca = inet_csk_ca(sk); | |
264 | ||
265 | if (after(ack, ca->end_seq)) | |
266 | update_params(sk); | |
267 | ||
268 | /* RFC2861 only increase cwnd if fully utilized */ | |
24901551 | 269 | if (!tcp_is_cwnd_limited(sk)) |
65d1b4a7 SH |
270 | return; |
271 | ||
272 | /* In slow start */ | |
071d5080 | 273 | if (tcp_in_slow_start(tp)) |
9f9843a7 | 274 | tcp_slow_start(tp, acked); |
65d1b4a7 SH |
275 | |
276 | else { | |
277 | u32 delta; | |
278 | ||
279 | /* snd_cwnd_cnt is # of packets since last cwnd increment */ | |
280 | tp->snd_cwnd_cnt += ca->acked; | |
281 | ca->acked = 1; | |
282 | ||
283 | /* This is close approximation of: | |
284 | * tp->snd_cwnd += alpha/tp->snd_cwnd | |
285 | */ | |
286 | delta = (tp->snd_cwnd_cnt * ca->alpha) >> ALPHA_SHIFT; | |
40570375 ED |
287 | if (delta >= tcp_snd_cwnd(tp)) { |
288 | tcp_snd_cwnd_set(tp, min(tcp_snd_cwnd(tp) + delta / tcp_snd_cwnd(tp), | |
289 | (u32)tp->snd_cwnd_clamp)); | |
65d1b4a7 SH |
290 | tp->snd_cwnd_cnt = 0; |
291 | } | |
292 | } | |
293 | } | |
294 | ||
c462238d SH |
295 | static u32 tcp_illinois_ssthresh(struct sock *sk) |
296 | { | |
297 | struct tcp_sock *tp = tcp_sk(sk); | |
65d1b4a7 | 298 | struct illinois *ca = inet_csk_ca(sk); |
40570375 | 299 | u32 decr; |
c462238d SH |
300 | |
301 | /* Multiplicative decrease */ | |
40570375 ED |
302 | decr = (tcp_snd_cwnd(tp) * ca->beta) >> BETA_SHIFT; |
303 | return max(tcp_snd_cwnd(tp) - decr, 2U); | |
c462238d SH |
304 | } |
305 | ||
65d1b4a7 | 306 | /* Extract info for Tcp socket info provided via netlink. */ |
64f40ff5 ED |
307 | static size_t tcp_illinois_info(struct sock *sk, u32 ext, int *attr, |
308 | union tcp_cc_info *info) | |
c462238d | 309 | { |
65d1b4a7 | 310 | const struct illinois *ca = inet_csk_ca(sk); |
c462238d SH |
311 | |
312 | if (ext & (1 << (INET_DIAG_VEGASINFO - 1))) { | |
64f40ff5 ED |
313 | info->vegas.tcpv_enabled = 1; |
314 | info->vegas.tcpv_rttcnt = ca->cnt_rtt; | |
315 | info->vegas.tcpv_minrtt = ca->base_rtt; | |
316 | info->vegas.tcpv_rtt = 0; | |
65d1b4a7 | 317 | |
64f40ff5 | 318 | if (info->vegas.tcpv_rttcnt > 0) { |
8f363b77 | 319 | u64 t = ca->sum_rtt; |
c462238d | 320 | |
64f40ff5 ED |
321 | do_div(t, info->vegas.tcpv_rttcnt); |
322 | info->vegas.tcpv_rtt = t; | |
8f363b77 | 323 | } |
64f40ff5 ED |
324 | *attr = INET_DIAG_VEGASINFO; |
325 | return sizeof(struct tcpvegas_info); | |
c462238d | 326 | } |
521f1cf1 | 327 | return 0; |
c462238d SH |
328 | } |
329 | ||
a252bebe | 330 | static struct tcp_congestion_ops tcp_illinois __read_mostly = { |
c462238d SH |
331 | .init = tcp_illinois_init, |
332 | .ssthresh = tcp_illinois_ssthresh, | |
f1722a1b | 333 | .undo_cwnd = tcp_reno_undo_cwnd, |
c462238d | 334 | .cong_avoid = tcp_illinois_cong_avoid, |
65d1b4a7 | 335 | .set_state = tcp_illinois_state, |
65d1b4a7 SH |
336 | .get_info = tcp_illinois_info, |
337 | .pkts_acked = tcp_illinois_acked, | |
c462238d SH |
338 | |
339 | .owner = THIS_MODULE, | |
340 | .name = "illinois", | |
341 | }; | |
342 | ||
343 | static int __init tcp_illinois_register(void) | |
344 | { | |
65d1b4a7 | 345 | BUILD_BUG_ON(sizeof(struct illinois) > ICSK_CA_PRIV_SIZE); |
c462238d SH |
346 | return tcp_register_congestion_control(&tcp_illinois); |
347 | } | |
348 | ||
349 | static void __exit tcp_illinois_unregister(void) | |
350 | { | |
351 | tcp_unregister_congestion_control(&tcp_illinois); | |
352 | } | |
353 | ||
354 | module_init(tcp_illinois_register); | |
355 | module_exit(tcp_illinois_unregister); | |
356 | ||
357 | MODULE_AUTHOR("Stephen Hemminger, Shao Liu"); | |
358 | MODULE_LICENSE("GPL"); | |
359 | MODULE_DESCRIPTION("TCP Illinois"); | |
65d1b4a7 | 360 | MODULE_VERSION("1.0"); |