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.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 */
  26 #define U32_MAX         ((u32)~0U)
  27 #define RTT_MAX         (U32_MAX / ALPHA_MAX)   /* 3.3 secs */
  28
  29 #define BETA_SHIFT      6
  30 #define BETA_SCALE      (1u<<BETA_SHIFT)
  31 #define BETA_MIN        (BETA_SCALE/8)          /* 0.125 */
  32 #define BETA_MAX        (BETA_SCALE/2)          /* 0.5 */
  33 #define BETA_BASE       BETA_MAX
  34
  35 static int win_thresh __read_mostly = 15;
  36 module_param(win_thresh, int, 0);
  37 MODULE_PARM_DESC(win_thresh, "Window threshold for starting adaptive sizing");
  38
  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");
  42
  43 /* TCP Illinois Parameters */
  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 */
  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, u32 pkts_acked, s32 rtt)
  87 {
  88         struct illinois *ca = inet_csk_ca(sk);
  89
  90         ca->acked = pkts_acked;
  91
  92         /* dup ack, no rtt sample */
  93         if (rtt < 0)
  94                 return;
  95
  96         /* ignore bogus values, this prevents wraparound in alpha math */
  97         if (rtt > RTT_MAX)
  98                 rtt = RTT_MAX;
  99
 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)
 106                 ca->max_rtt = rtt;
 107
 108         ++ca->cnt_rtt;
 109         ca->sum_rtt += rtt;
 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 in_flight)
 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
 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
 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)
 307 {
 308         const struct illinois *ca = inet_csk_ca(sk);
 309
 310         if (ext & (1 << (INET_DIAG_VEGASINFO - 1))) {
 311                 struct tcpvegas_info info = {
 312                         .tcpv_enabled = 1,
 313                         .tcpv_rttcnt = ca->cnt_rtt,
 314                         .tcpv_minrtt = ca->base_rtt,
 315                 };
 316                 u64 t = ca->sum_rtt;
 317
 318                 do_div(t, ca->cnt_rtt);
 319                 info.tcpv_rtt = t;
 320
 321                 nla_put(skb, INET_DIAG_VEGASINFO, sizeof(info), &info);
 322         }
 323 }
 324
 325 static struct tcp_congestion_ops tcp_illinois = {
 326         .flags          = TCP_CONG_RTT_STAMP,
 327         .init           = tcp_illinois_init,
 328         .ssthresh       = tcp_illinois_ssthresh,
 329         .min_cwnd       = tcp_reno_min_cwnd,
 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");