net/ipv4/tcp_illinois.c

   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         u32     loss_cwnd;      /* cwnd on loss */
  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 */
  55 };
  56
  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
  69 static void tcp_illinois_init(struct sock *sk)
  70 {
  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;
  81
  82         rtt_reset(sk);
  83 }
  84
  85 /* Measure RTT for each ack. */
  86 static void tcp_illinois_acked(struct sock *sk, const struct ack_sample *sample)
  87 {
  88         struct illinois *ca = inet_csk_ca(sk);
  89         s32 rtt_us = sample->rtt_us;
  90
  91         ca->acked = sample->pkts_acked;
  92
  93         /* dup ack, no rtt sample */
  94         if (rtt_us < 0)
  95                 return;
  96
  97         /* ignore bogus values, this prevents wraparound in alpha math */
  98         if (rtt_us > RTT_MAX)
  99                 rtt_us = RTT_MAX;
 100
 101         /* keep track of minimum RTT seen so far */
 102         if (ca->base_rtt > rtt_us)
 103                 ca->base_rtt = rtt_us;
 104
 105         /* and max */
 106         if (ca->max_rtt < rtt_us)
 107                 ca->max_rtt = rtt_us;
 108
 109         ++ca->cnt_rtt;
 110         ca->sum_rtt += rtt_us;
 111 }
 112
 113 /* Maximum queuing delay */
 114 static inline u32 max_delay(const struct illinois *ca)
 115 {
 116         return ca->max_rtt - ca->base_rtt;
 117 }
 118
 119 /* Average queuing delay */
 120 static inline u32 avg_delay(const struct illinois *ca)
 121 {
 122         u64 t = ca->sum_rtt;
 123
 124         do_div(t, ca->cnt_rtt);
 125         return t - ca->base_rtt;
 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)
 136  *    then use small alpha (0.3)
 137  *
 138  * The result is a convex window growth curve.
 139  */
 140 static u32 alpha(struct illinois *ca, u32 da, u32 dm)
 141 {
 142         u32 d1 = dm / 100;      /* Low threshold */
 143
 144         if (da <= d1) {
 145                 /* If never got out of low delay zone, then use max */
 146                 if (!ca->rtt_above)
 147                         return ALPHA_MAX;
 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;
 158         }
 159
 160         ca->rtt_above = 1;
 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;
 180         return (dm * ALPHA_MAX) /
 181                 (dm + (da  * (ALPHA_MAX - ALPHA_MIN)) / ALPHA_MIN);
 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  */
 192 static u32 beta(u32 da, u32 dm)
 193 {
 194         u32 d2, d3;
 195
 196         d2 = dm / 10;
 197         if (da <= d2)
 198                 return BETA_MIN;
 199
 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
 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
 227         if (tp->snd_cwnd < win_thresh) {
 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  */
 260 static void tcp_illinois_cong_avoid(struct sock *sk, u32 ack, u32 acked)
 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 */
 269         if (!tcp_is_cwnd_limited(sk))
 270                 return;
 271
 272         /* In slow start */
 273         if (tcp_in_slow_start(tp))
 274                 tcp_slow_start(tp, acked);
 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;
 287                 if (delta >= tp->snd_cwnd) {
 288                         tp->snd_cwnd = min(tp->snd_cwnd + delta / tp->snd_cwnd,
 289                                            (u32)tp->snd_cwnd_clamp);
 290                         tp->snd_cwnd_cnt = 0;
 291                 }
 292         }
 293 }
 294
 295 static u32 tcp_illinois_ssthresh(struct sock *sk)
 296 {
 297         struct tcp_sock *tp = tcp_sk(sk);
 298         struct illinois *ca = inet_csk_ca(sk);
 299
 300         ca->loss_cwnd = tp->snd_cwnd;
 301         /* Multiplicative decrease */
 302         return max(tp->snd_cwnd - ((tp->snd_cwnd * ca->beta) >> BETA_SHIFT), 2U);
 303 }
 304
 305 static u32 tcp_illinois_cwnd_undo(struct sock *sk)
 306 {
 307         const struct illinois *ca = inet_csk_ca(sk);
 308
 309         return max(tcp_sk(sk)->snd_cwnd, ca->loss_cwnd);
 310 }
 311
 312 /* Extract info for Tcp socket info provided via netlink. */
 313 static size_t tcp_illinois_info(struct sock *sk, u32 ext, int *attr,
 314                                 union tcp_cc_info *info)
 315 {
 316         const struct illinois *ca = inet_csk_ca(sk);
 317
 318         if (ext & (1 << (INET_DIAG_VEGASINFO - 1))) {
 319                 info->vegas.tcpv_enabled = 1;
 320                 info->vegas.tcpv_rttcnt = ca->cnt_rtt;
 321                 info->vegas.tcpv_minrtt = ca->base_rtt;
 322                 info->vegas.tcpv_rtt = 0;
 323
 324                 if (info->vegas.tcpv_rttcnt > 0) {
 325                         u64 t = ca->sum_rtt;
 326
 327                         do_div(t, info->vegas.tcpv_rttcnt);
 328                         info->vegas.tcpv_rtt = t;
 329                 }
 330                 *attr = INET_DIAG_VEGASINFO;
 331                 return sizeof(struct tcpvegas_info);
 332         }
 333         return 0;
 334 }
 335
 336 static struct tcp_congestion_ops tcp_illinois __read_mostly = {
 337         .init           = tcp_illinois_init,
 338         .ssthresh       = tcp_illinois_ssthresh,
 339         .undo_cwnd      = tcp_illinois_cwnd_undo,
 340         .cong_avoid     = tcp_illinois_cong_avoid,
 341         .set_state      = tcp_illinois_state,
 342         .get_info       = tcp_illinois_info,
 343         .pkts_acked     = tcp_illinois_acked,
 344
 345         .owner          = THIS_MODULE,
 346         .name           = "illinois",
 347 };
 348
 349 static int __init tcp_illinois_register(void)
 350 {
 351         BUILD_BUG_ON(sizeof(struct illinois) > ICSK_CA_PRIV_SIZE);
 352         return tcp_register_congestion_control(&tcp_illinois);
 353 }
 354
 355 static void __exit tcp_illinois_unregister(void)
 356 {
 357         tcp_unregister_congestion_control(&tcp_illinois);
 358 }
 359
 360 module_init(tcp_illinois_register);
 361 module_exit(tcp_illinois_unregister);
 362
 363 MODULE_AUTHOR("Stephen Hemminger, Shao Liu");
 364 MODULE_LICENSE("GPL");
 365 MODULE_DESCRIPTION("TCP Illinois");
 366 MODULE_VERSION("1.0");