Commit | Line | Data |
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c462238d SH |
1 | /* |
2 | * TCP Illinois congestion control. | |
3 | * Home page: | |
4 | * http://www.ews.uiuc.edu/~shaoliu/tcpillinois/index.html | |
5 | * | |
6 | * The algorithm is described in: | |
7 | * "TCP-Illinois: A Loss and Delay-Based Congestion Control Algorithm | |
8 | * for High-Speed Networks" | |
9 | * http://www.ews.uiuc.edu/~shaoliu/papersandslides/liubassri06perf.pdf | |
10 | * | |
11 | * Implemented from description in paper and ns-2 simulation. | |
12 | * Copyright (C) 2007 Stephen Hemminger <shemminger@linux-foundation.org> | |
13 | */ | |
14 | ||
15 | #include <linux/module.h> | |
16 | #include <linux/skbuff.h> | |
17 | #include <linux/inet_diag.h> | |
18 | #include <asm/div64.h> | |
19 | #include <net/tcp.h> | |
20 | ||
21 | #define ALPHA_SHIFT 7 | |
22 | #define ALPHA_SCALE (1u<<ALPHA_SHIFT) | |
23 | #define ALPHA_MIN ((3*ALPHA_SCALE)/10) /* ~0.3 */ | |
24 | #define ALPHA_MAX (10*ALPHA_SCALE) /* 10.0 */ | |
25 | #define ALPHA_BASE ALPHA_SCALE /* 1.0 */ | |
65d1b4a7 SH |
26 | #define U32_MAX ((u32)~0U) |
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. */ |
30cfd0ba | 86 | static void tcp_illinois_acked(struct sock *sk, u32 pkts_acked, s32 rtt) |
c462238d | 87 | { |
65d1b4a7 | 88 | struct illinois *ca = inet_csk_ca(sk); |
164891aa SH |
89 | |
90 | ca->acked = pkts_acked; | |
91 | ||
30cfd0ba SH |
92 | /* dup ack, no rtt sample */ |
93 | if (rtt < 0) | |
b9ce204f IJ |
94 | return; |
95 | ||
65d1b4a7 SH |
96 | /* ignore bogus values, this prevents wraparound in alpha math */ |
97 | if (rtt > RTT_MAX) | |
98 | rtt = RTT_MAX; | |
c462238d | 99 | |
65d1b4a7 SH |
100 | /* keep track of minimum RTT seen so far */ |
101 | if (ca->base_rtt > rtt) | |
102 | ca->base_rtt = rtt; | |
103 | ||
104 | /* and max */ | |
105 | if (ca->max_rtt < rtt) | |
c462238d SH |
106 | ca->max_rtt = rtt; |
107 | ||
65d1b4a7 SH |
108 | ++ca->cnt_rtt; |
109 | ca->sum_rtt += rtt; | |
c462238d SH |
110 | } |
111 | ||
65d1b4a7 SH |
112 | /* Maximum queuing delay */ |
113 | static inline u32 max_delay(const struct illinois *ca) | |
c462238d | 114 | { |
65d1b4a7 SH |
115 | return ca->max_rtt - ca->base_rtt; |
116 | } | |
c462238d | 117 | |
65d1b4a7 SH |
118 | /* Average queuing delay */ |
119 | static inline u32 avg_delay(const struct illinois *ca) | |
120 | { | |
121 | u64 t = ca->sum_rtt; | |
c462238d | 122 | |
65d1b4a7 SH |
123 | do_div(t, ca->cnt_rtt); |
124 | return t - ca->base_rtt; | |
c462238d SH |
125 | } |
126 | ||
127 | /* | |
128 | * Compute value of alpha used for additive increase. | |
129 | * If small window then use 1.0, equivalent to Reno. | |
130 | * | |
131 | * For larger windows, adjust based on average delay. | |
132 | * A. If average delay is at minimum (we are uncongested), | |
133 | * then use large alpha (10.0) to increase faster. | |
134 | * B. If average delay is at maximum (getting congested) | |
65d1b4a7 | 135 | * then use small alpha (0.3) |
c462238d SH |
136 | * |
137 | * The result is a convex window growth curve. | |
138 | */ | |
65d1b4a7 | 139 | static u32 alpha(struct illinois *ca, u32 da, u32 dm) |
c462238d | 140 | { |
65d1b4a7 | 141 | u32 d1 = dm / 100; /* Low threshold */ |
c462238d | 142 | |
c462238d | 143 | if (da <= d1) { |
65d1b4a7 SH |
144 | /* If never got out of low delay zone, then use max */ |
145 | if (!ca->rtt_above) | |
c462238d | 146 | return ALPHA_MAX; |
65d1b4a7 SH |
147 | |
148 | /* Wait for 5 good RTT's before allowing alpha to go alpha max. | |
149 | * This prevents one good RTT from causing sudden window increase. | |
150 | */ | |
151 | if (++ca->rtt_low < theta) | |
152 | return ca->alpha; | |
153 | ||
154 | ca->rtt_low = 0; | |
155 | ca->rtt_above = 0; | |
156 | return ALPHA_MAX; | |
c462238d SH |
157 | } |
158 | ||
65d1b4a7 | 159 | ca->rtt_above = 1; |
c462238d SH |
160 | |
161 | /* | |
162 | * Based on: | |
163 | * | |
164 | * (dm - d1) amin amax | |
165 | * k1 = ------------------- | |
166 | * amax - amin | |
167 | * | |
168 | * (dm - d1) amin | |
169 | * k2 = ---------------- - d1 | |
170 | * amax - amin | |
171 | * | |
172 | * k1 | |
173 | * alpha = ---------- | |
174 | * k2 + da | |
175 | */ | |
176 | ||
177 | dm -= d1; | |
178 | da -= d1; | |
65d1b4a7 SH |
179 | return (dm * ALPHA_MAX) / |
180 | (dm + (da * (ALPHA_MAX - ALPHA_MIN)) / ALPHA_MIN); | |
c462238d SH |
181 | } |
182 | ||
183 | /* | |
184 | * Beta used for multiplicative decrease. | |
185 | * For small window sizes returns same value as Reno (0.5) | |
186 | * | |
187 | * If delay is small (10% of max) then beta = 1/8 | |
188 | * If delay is up to 80% of max then beta = 1/2 | |
189 | * In between is a linear function | |
190 | */ | |
65d1b4a7 | 191 | static u32 beta(u32 da, u32 dm) |
c462238d | 192 | { |
c462238d SH |
193 | u32 d2, d3; |
194 | ||
c462238d SH |
195 | d2 = dm / 10; |
196 | if (da <= d2) | |
197 | return BETA_MIN; | |
65d1b4a7 | 198 | |
c462238d SH |
199 | d3 = (8 * dm) / 10; |
200 | if (da >= d3 || d3 <= d2) | |
201 | return BETA_MAX; | |
202 | ||
203 | /* | |
204 | * Based on: | |
205 | * | |
206 | * bmin d3 - bmax d2 | |
207 | * k3 = ------------------- | |
208 | * d3 - d2 | |
209 | * | |
210 | * bmax - bmin | |
211 | * k4 = ------------- | |
212 | * d3 - d2 | |
213 | * | |
214 | * b = k3 + k4 da | |
215 | */ | |
216 | return (BETA_MIN * d3 - BETA_MAX * d2 + (BETA_MAX - BETA_MIN) * da) | |
217 | / (d3 - d2); | |
218 | } | |
219 | ||
65d1b4a7 SH |
220 | /* Update alpha and beta values once per RTT */ |
221 | static void update_params(struct sock *sk) | |
222 | { | |
223 | struct tcp_sock *tp = tcp_sk(sk); | |
224 | struct illinois *ca = inet_csk_ca(sk); | |
225 | ||
226 | if (tp->snd_cwnd < win_thresh) { | |
227 | ca->alpha = ALPHA_BASE; | |
228 | ca->beta = BETA_BASE; | |
229 | } else if (ca->cnt_rtt > 0) { | |
230 | u32 dm = max_delay(ca); | |
231 | u32 da = avg_delay(ca); | |
232 | ||
233 | ca->alpha = alpha(ca, da, dm); | |
234 | ca->beta = beta(da, dm); | |
235 | } | |
236 | ||
237 | rtt_reset(sk); | |
238 | } | |
239 | ||
240 | /* | |
241 | * In case of loss, reset to default values | |
242 | */ | |
243 | static void tcp_illinois_state(struct sock *sk, u8 new_state) | |
244 | { | |
245 | struct illinois *ca = inet_csk_ca(sk); | |
246 | ||
247 | if (new_state == TCP_CA_Loss) { | |
248 | ca->alpha = ALPHA_BASE; | |
249 | ca->beta = BETA_BASE; | |
250 | ca->rtt_low = 0; | |
251 | ca->rtt_above = 0; | |
252 | rtt_reset(sk); | |
253 | } | |
254 | } | |
255 | ||
256 | /* | |
257 | * Increase window in response to successful acknowledgment. | |
258 | */ | |
c3a05c60 | 259 | static void tcp_illinois_cong_avoid(struct sock *sk, u32 ack, u32 in_flight) |
65d1b4a7 SH |
260 | { |
261 | struct tcp_sock *tp = tcp_sk(sk); | |
262 | struct illinois *ca = inet_csk_ca(sk); | |
263 | ||
264 | if (after(ack, ca->end_seq)) | |
265 | update_params(sk); | |
266 | ||
267 | /* RFC2861 only increase cwnd if fully utilized */ | |
268 | if (!tcp_is_cwnd_limited(sk, in_flight)) | |
269 | return; | |
270 | ||
271 | /* In slow start */ | |
272 | if (tp->snd_cwnd <= tp->snd_ssthresh) | |
273 | tcp_slow_start(tp); | |
274 | ||
275 | else { | |
276 | u32 delta; | |
277 | ||
278 | /* snd_cwnd_cnt is # of packets since last cwnd increment */ | |
279 | tp->snd_cwnd_cnt += ca->acked; | |
280 | ca->acked = 1; | |
281 | ||
282 | /* This is close approximation of: | |
283 | * tp->snd_cwnd += alpha/tp->snd_cwnd | |
284 | */ | |
285 | delta = (tp->snd_cwnd_cnt * ca->alpha) >> ALPHA_SHIFT; | |
286 | if (delta >= tp->snd_cwnd) { | |
287 | tp->snd_cwnd = min(tp->snd_cwnd + delta / tp->snd_cwnd, | |
288 | (u32) tp->snd_cwnd_clamp); | |
289 | tp->snd_cwnd_cnt = 0; | |
290 | } | |
291 | } | |
292 | } | |
293 | ||
c462238d SH |
294 | static u32 tcp_illinois_ssthresh(struct sock *sk) |
295 | { | |
296 | struct tcp_sock *tp = tcp_sk(sk); | |
65d1b4a7 | 297 | struct illinois *ca = inet_csk_ca(sk); |
c462238d SH |
298 | |
299 | /* Multiplicative decrease */ | |
a357dde9 | 300 | return max(tp->snd_cwnd - ((tp->snd_cwnd * ca->beta) >> BETA_SHIFT), 2U); |
c462238d SH |
301 | } |
302 | ||
65d1b4a7 SH |
303 | |
304 | /* Extract info for Tcp socket info provided via netlink. */ | |
305 | static void tcp_illinois_info(struct sock *sk, u32 ext, | |
306 | struct sk_buff *skb) | |
c462238d | 307 | { |
65d1b4a7 | 308 | const struct illinois *ca = inet_csk_ca(sk); |
c462238d SH |
309 | |
310 | if (ext & (1 << (INET_DIAG_VEGASINFO - 1))) { | |
311 | struct tcpvegas_info info = { | |
312 | .tcpv_enabled = 1, | |
65d1b4a7 SH |
313 | .tcpv_rttcnt = ca->cnt_rtt, |
314 | .tcpv_minrtt = ca->base_rtt, | |
c462238d | 315 | }; |
65d1b4a7 SH |
316 | u64 t = ca->sum_rtt; |
317 | ||
318 | do_div(t, ca->cnt_rtt); | |
319 | info.tcpv_rtt = t; | |
c462238d SH |
320 | |
321 | nla_put(skb, INET_DIAG_VEGASINFO, sizeof(info), &info); | |
322 | } | |
323 | } | |
324 | ||
325 | static struct tcp_congestion_ops tcp_illinois = { | |
164891aa | 326 | .flags = TCP_CONG_RTT_STAMP, |
c462238d SH |
327 | .init = tcp_illinois_init, |
328 | .ssthresh = tcp_illinois_ssthresh, | |
329 | .min_cwnd = tcp_reno_min_cwnd, | |
330 | .cong_avoid = tcp_illinois_cong_avoid, | |
65d1b4a7 | 331 | .set_state = tcp_illinois_state, |
65d1b4a7 SH |
332 | .get_info = tcp_illinois_info, |
333 | .pkts_acked = tcp_illinois_acked, | |
c462238d SH |
334 | |
335 | .owner = THIS_MODULE, | |
336 | .name = "illinois", | |
337 | }; | |
338 | ||
339 | static int __init tcp_illinois_register(void) | |
340 | { | |
65d1b4a7 | 341 | BUILD_BUG_ON(sizeof(struct illinois) > ICSK_CA_PRIV_SIZE); |
c462238d SH |
342 | return tcp_register_congestion_control(&tcp_illinois); |
343 | } | |
344 | ||
345 | static void __exit tcp_illinois_unregister(void) | |
346 | { | |
347 | tcp_unregister_congestion_control(&tcp_illinois); | |
348 | } | |
349 | ||
350 | module_init(tcp_illinois_register); | |
351 | module_exit(tcp_illinois_unregister); | |
352 | ||
353 | MODULE_AUTHOR("Stephen Hemminger, Shao Liu"); | |
354 | MODULE_LICENSE("GPL"); | |
355 | MODULE_DESCRIPTION("TCP Illinois"); | |
65d1b4a7 | 356 | MODULE_VERSION("1.0"); |