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Linux/net/ipv4/tcp_illinois.c

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  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.ifp.illinois.edu/~srikant/Papers/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 */
 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 
 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 
 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. */
 85 static void tcp_illinois_acked(struct sock *sk, const struct ack_sample *sample)
 86 {
 87         struct illinois *ca = inet_csk_ca(sk);
 88         s32 rtt_us = sample->rtt_us;
 89 
 90         ca->acked = sample->pkts_acked;
 91 
 92         /* dup ack, no rtt sample */
 93         if (rtt_us < 0)
 94                 return;
 95 
 96         /* ignore bogus values, this prevents wraparound in alpha math */
 97         if (rtt_us > RTT_MAX)
 98                 rtt_us = RTT_MAX;
 99 
100         /* keep track of minimum RTT seen so far */
101         if (ca->base_rtt > rtt_us)
102                 ca->base_rtt = rtt_us;
103 
104         /* and max */
105         if (ca->max_rtt < rtt_us)
106                 ca->max_rtt = rtt_us;
107 
108         ++ca->cnt_rtt;
109         ca->sum_rtt += rtt_us;
110 }
111 
112 /* Maximum queuing delay */
113 static inline u32 max_delay(const struct illinois *ca)
114 {
115         return ca->max_rtt - ca->base_rtt;
116 }
117 
118 /* Average queuing delay */
119 static inline u32 avg_delay(const struct illinois *ca)
120 {
121         u64 t = ca->sum_rtt;
122 
123         do_div(t, ca->cnt_rtt);
124         return t - ca->base_rtt;
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)
135  *    then use small alpha (0.3)
136  *
137  * The result is a convex window growth curve.
138  */
139 static u32 alpha(struct illinois *ca, u32 da, u32 dm)
140 {
141         u32 d1 = dm / 100;      /* Low threshold */
142 
143         if (da <= d1) {
144                 /* If never got out of low delay zone, then use max */
145                 if (!ca->rtt_above)
146                         return ALPHA_MAX;
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;
157         }
158 
159         ca->rtt_above = 1;
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;
179         return (dm * ALPHA_MAX) /
180                 (dm + (da  * (ALPHA_MAX - ALPHA_MIN)) / ALPHA_MIN);
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  */
191 static u32 beta(u32 da, u32 dm)
192 {
193         u32 d2, d3;
194 
195         d2 = dm / 10;
196         if (da <= d2)
197                 return BETA_MIN;
198 
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 
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  */
259 static void tcp_illinois_cong_avoid(struct sock *sk, u32 ack, u32 acked)
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))
269                 return;
270 
271         /* In slow start */
272         if (tcp_in_slow_start(tp))
273                 tcp_slow_start(tp, acked);
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 
294 static u32 tcp_illinois_ssthresh(struct sock *sk)
295 {
296         struct tcp_sock *tp = tcp_sk(sk);
297         struct illinois *ca = inet_csk_ca(sk);
298 
299         /* Multiplicative decrease */
300         return max(tp->snd_cwnd - ((tp->snd_cwnd * ca->beta) >> BETA_SHIFT), 2U);
301 }
302 
303 /* Extract info for Tcp socket info provided via netlink. */
304 static size_t tcp_illinois_info(struct sock *sk, u32 ext, int *attr,
305                                 union tcp_cc_info *info)
306 {
307         const struct illinois *ca = inet_csk_ca(sk);
308 
309         if (ext & (1 << (INET_DIAG_VEGASINFO - 1))) {
310                 info->vegas.tcpv_enabled = 1;
311                 info->vegas.tcpv_rttcnt = ca->cnt_rtt;
312                 info->vegas.tcpv_minrtt = ca->base_rtt;
313                 info->vegas.tcpv_rtt = 0;
314 
315                 if (info->vegas.tcpv_rttcnt > 0) {
316                         u64 t = ca->sum_rtt;
317 
318                         do_div(t, info->vegas.tcpv_rttcnt);
319                         info->vegas.tcpv_rtt = t;
320                 }
321                 *attr = INET_DIAG_VEGASINFO;
322                 return sizeof(struct tcpvegas_info);
323         }
324         return 0;
325 }
326 
327 static struct tcp_congestion_ops tcp_illinois __read_mostly = {
328         .init           = tcp_illinois_init,
329         .ssthresh       = tcp_illinois_ssthresh,
330         .cong_avoid     = tcp_illinois_cong_avoid,
331         .set_state      = tcp_illinois_state,
332         .get_info       = tcp_illinois_info,
333         .pkts_acked     = tcp_illinois_acked,
334 
335         .owner          = THIS_MODULE,
336         .name           = "illinois",
337 };
338 
339 static int __init tcp_illinois_register(void)
340 {
341         BUILD_BUG_ON(sizeof(struct illinois) > ICSK_CA_PRIV_SIZE);
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");
356 MODULE_VERSION("1.0");
357 

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