net/ipv4/tcp_illinois.c

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This source file includes following definitions.
rtt_reset
tcp_illinois_init
tcp_illinois_acked
max_delay
avg_delay
alpha
beta
update_params
tcp_illinois_state
tcp_illinois_cong_avoid
tcp_illinois_ssthresh
tcp_illinois_info
tcp_illinois_register
tcp_illinois_unregister
   1 // SPDX-License-Identifier: GPL-2.0-only
   2 /*
   3  * TCP Illinois congestion control.
   4  * Home page:
   5  *      http://www.ews.uiuc.edu/~shaoliu/tcpillinois/index.html
   6  *
   7  * The algorithm is described in:
   8  * "TCP-Illinois: A Loss and Delay-Based Congestion Control Algorithm
   9  *  for High-Speed Networks"
  10  * http://tamerbasar.csl.illinois.edu/LiuBasarSrikantPerfEvalArtJun2008.pdf
  11  *
  12  * Implemented from description in paper and ns-2 simulation.
  13  * Copyright (C) 2007 Stephen Hemminger <shemminger@linux-foundation.org>
  14  */
  15 
  16 #include <linux/module.h>
  17 #include <linux/skbuff.h>
  18 #include <linux/inet_diag.h>
  19 #include <asm/div64.h>
  20 #include <net/tcp.h>
  21 
  22 #define ALPHA_SHIFT     7
  23 #define ALPHA_SCALE     (1u<<ALPHA_SHIFT)
  24 #define ALPHA_MIN       ((3*ALPHA_SCALE)/10)    /* ~0.3 */
  25 #define ALPHA_MAX       (10*ALPHA_SCALE)        /* 10.0 */
  26 #define ALPHA_BASE      ALPHA_SCALE             /* 1.0 */
  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, 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         /* Multiplicative decrease */
 301         return max(tp->snd_cwnd - ((tp->snd_cwnd * ca->beta) >> BETA_SHIFT), 2U);
 302 }
 303 
 304 /* Extract info for Tcp socket info provided via netlink. */
 305 static size_t tcp_illinois_info(struct sock *sk, u32 ext, int *attr,
 306                                 union tcp_cc_info *info)
 307 {
 308         const struct illinois *ca = inet_csk_ca(sk);
 309 
 310         if (ext & (1 << (INET_DIAG_VEGASINFO - 1))) {
 311                 info->vegas.tcpv_enabled = 1;
 312                 info->vegas.tcpv_rttcnt = ca->cnt_rtt;
 313                 info->vegas.tcpv_minrtt = ca->base_rtt;
 314                 info->vegas.tcpv_rtt = 0;
 315 
 316                 if (info->vegas.tcpv_rttcnt > 0) {
 317                         u64 t = ca->sum_rtt;
 318 
 319                         do_div(t, info->vegas.tcpv_rttcnt);
 320                         info->vegas.tcpv_rtt = t;
 321                 }
 322                 *attr = INET_DIAG_VEGASINFO;
 323                 return sizeof(struct tcpvegas_info);
 324         }
 325         return 0;
 326 }
 327 
 328 static struct tcp_congestion_ops tcp_illinois __read_mostly = {
 329         .init           = tcp_illinois_init,
 330         .ssthresh       = tcp_illinois_ssthresh,
 331         .undo_cwnd      = tcp_reno_undo_cwnd,
 332         .cong_avoid     = tcp_illinois_cong_avoid,
 333         .set_state      = tcp_illinois_state,
 334         .get_info       = tcp_illinois_info,
 335         .pkts_acked     = tcp_illinois_acked,
 336 
 337         .owner          = THIS_MODULE,
 338         .name           = "illinois",
 339 };
 340 
 341 static int __init tcp_illinois_register(void)
 342 {
 343         BUILD_BUG_ON(sizeof(struct illinois) > ICSK_CA_PRIV_SIZE);
 344         return tcp_register_congestion_control(&tcp_illinois);
 345 }
 346 
 347 static void __exit tcp_illinois_unregister(void)
 348 {
 349         tcp_unregister_congestion_control(&tcp_illinois);
 350 }
 351 
 352 module_init(tcp_illinois_register);
 353 module_exit(tcp_illinois_unregister);
 354 
 355 MODULE_AUTHOR("Stephen Hemminger, Shao Liu");
 356 MODULE_LICENSE("GPL");
 357 MODULE_DESCRIPTION("TCP Illinois");
 358 MODULE_VERSION("1.0");
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root/net/ipv4/tcp_illinois.c

DEFINITIONS
