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         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, 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 */
 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 */
 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  */
 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  */
 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 */
 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  */
 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  */
 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 (tp->snd_cwnd <= tp->snd_ssthresh)
 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
 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
 303 /* Extract info for Tcp socket info provided via netlink. */
 304 static void tcp_illinois_info(struct sock *sk, u32 ext,
 305                               struct sk_buff *skb)
 306 {
 307         const struct illinois *ca = inet_csk_ca(sk);
 308
 309         if (ext & (1 << (INET_DIAG_VEGASINFO - 1))) {
 310                 struct tcpvegas_info info = {
 311                         .tcpv_enabled = 1,
 312                         .tcpv_rttcnt = ca->cnt_rtt,
 313                         .tcpv_minrtt = ca->base_rtt,
 314                 };
 315
 316                 if (info.tcpv_rttcnt > 0) {
 317                         u64 t = ca->sum_rtt;
 318
 319                         do_div(t, info.tcpv_rttcnt);
 320                         info.tcpv_rtt = t;
 321                 }
 322                 nla_put(skb, INET_DIAG_VEGASINFO, sizeof(info), &info);
 323         }
 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
 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
 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");