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