linux/net/ipv4/tcp_highspeed.c
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   1/*
   2 * Sally Floyd's High Speed TCP (RFC 3649) congestion control
   3 *
   4 * See http://www.icir.org/floyd/hstcp.html
   5 *
   6 * John Heffner <jheffner@psc.edu>
   7 */
   8
   9#include <linux/module.h>
  10#include <net/tcp.h>
  11
  12
  13/* From AIMD tables from RFC 3649 appendix B,
  14 * with fixed-point MD scaled <<8.
  15 */
  16static const struct hstcp_aimd_val {
  17        unsigned int cwnd;
  18        unsigned int md;
  19} hstcp_aimd_vals[] = {
  20 {     38,  128, /*  0.50 */ },
  21 {    118,  112, /*  0.44 */ },
  22 {    221,  104, /*  0.41 */ },
  23 {    347,   98, /*  0.38 */ },
  24 {    495,   93, /*  0.37 */ },
  25 {    663,   89, /*  0.35 */ },
  26 {    851,   86, /*  0.34 */ },
  27 {   1058,   83, /*  0.33 */ },
  28 {   1284,   81, /*  0.32 */ },
  29 {   1529,   78, /*  0.31 */ },
  30 {   1793,   76, /*  0.30 */ },
  31 {   2076,   74, /*  0.29 */ },
  32 {   2378,   72, /*  0.28 */ },
  33 {   2699,   71, /*  0.28 */ },
  34 {   3039,   69, /*  0.27 */ },
  35 {   3399,   68, /*  0.27 */ },
  36 {   3778,   66, /*  0.26 */ },
  37 {   4177,   65, /*  0.26 */ },
  38 {   4596,   64, /*  0.25 */ },
  39 {   5036,   62, /*  0.25 */ },
  40 {   5497,   61, /*  0.24 */ },
  41 {   5979,   60, /*  0.24 */ },
  42 {   6483,   59, /*  0.23 */ },
  43 {   7009,   58, /*  0.23 */ },
  44 {   7558,   57, /*  0.22 */ },
  45 {   8130,   56, /*  0.22 */ },
  46 {   8726,   55, /*  0.22 */ },
  47 {   9346,   54, /*  0.21 */ },
  48 {   9991,   53, /*  0.21 */ },
  49 {  10661,   52, /*  0.21 */ },
  50 {  11358,   52, /*  0.20 */ },
  51 {  12082,   51, /*  0.20 */ },
  52 {  12834,   50, /*  0.20 */ },
  53 {  13614,   49, /*  0.19 */ },
  54 {  14424,   48, /*  0.19 */ },
  55 {  15265,   48, /*  0.19 */ },
  56 {  16137,   47, /*  0.19 */ },
  57 {  17042,   46, /*  0.18 */ },
  58 {  17981,   45, /*  0.18 */ },
  59 {  18955,   45, /*  0.18 */ },
  60 {  19965,   44, /*  0.17 */ },
  61 {  21013,   43, /*  0.17 */ },
  62 {  22101,   43, /*  0.17 */ },
  63 {  23230,   42, /*  0.17 */ },
  64 {  24402,   41, /*  0.16 */ },
  65 {  25618,   41, /*  0.16 */ },
  66 {  26881,   40, /*  0.16 */ },
  67 {  28193,   39, /*  0.16 */ },
  68 {  29557,   39, /*  0.15 */ },
  69 {  30975,   38, /*  0.15 */ },
  70 {  32450,   38, /*  0.15 */ },
  71 {  33986,   37, /*  0.15 */ },
  72 {  35586,   36, /*  0.14 */ },
  73 {  37253,   36, /*  0.14 */ },
  74 {  38992,   35, /*  0.14 */ },
  75 {  40808,   35, /*  0.14 */ },
  76 {  42707,   34, /*  0.13 */ },
  77 {  44694,   33, /*  0.13 */ },
  78 {  46776,   33, /*  0.13 */ },
  79 {  48961,   32, /*  0.13 */ },
  80 {  51258,   32, /*  0.13 */ },
  81 {  53677,   31, /*  0.12 */ },
  82 {  56230,   30, /*  0.12 */ },
  83 {  58932,   30, /*  0.12 */ },
  84 {  61799,   29, /*  0.12 */ },
  85 {  64851,   28, /*  0.11 */ },
  86 {  68113,   28, /*  0.11 */ },
  87 {  71617,   27, /*  0.11 */ },
  88 {  75401,   26, /*  0.10 */ },
  89 {  79517,   26, /*  0.10 */ },
  90 {  84035,   25, /*  0.10 */ },
  91 {  89053,   24, /*  0.10 */ },
  92};
  93
  94#define HSTCP_AIMD_MAX  ARRAY_SIZE(hstcp_aimd_vals)
  95
  96struct hstcp {
  97        u32     ai;
  98};
  99
 100static void hstcp_init(struct sock *sk)
 101{
 102        struct tcp_sock *tp = tcp_sk(sk);
 103        struct hstcp *ca = inet_csk_ca(sk);
 104
 105        ca->ai = 0;
 106
 107        /* Ensure the MD arithmetic works.  This is somewhat pedantic,
 108         * since I don't think we will see a cwnd this large. :) */
 109        tp->snd_cwnd_clamp = min_t(u32, tp->snd_cwnd_clamp, 0xffffffff/128);
 110}
 111
 112static void hstcp_cong_avoid(struct sock *sk, u32 adk, u32 in_flight)
 113{
 114        struct tcp_sock *tp = tcp_sk(sk);
 115        struct hstcp *ca = inet_csk_ca(sk);
 116
 117        if (!tcp_is_cwnd_limited(sk, in_flight))
 118                return;
 119
 120        if (tp->snd_cwnd <= tp->snd_ssthresh)
 121                tcp_slow_start(tp);
 122        else {
 123                /* Update AIMD parameters.
 124                 *
 125                 * We want to guarantee that:
 126                 *     hstcp_aimd_vals[ca->ai-1].cwnd <
 127                 *     snd_cwnd <=
 128                 *     hstcp_aimd_vals[ca->ai].cwnd
 129                 */
 130                if (tp->snd_cwnd > hstcp_aimd_vals[ca->ai].cwnd) {
 131                        while (tp->snd_cwnd > hstcp_aimd_vals[ca->ai].cwnd &&
 132                               ca->ai < HSTCP_AIMD_MAX - 1)
 133                                ca->ai++;
 134                } else if (ca->ai && tp->snd_cwnd <= hstcp_aimd_vals[ca->ai-1].cwnd) {
 135                        while (ca->ai && tp->snd_cwnd <= hstcp_aimd_vals[ca->ai-1].cwnd)
 136                                ca->ai--;
 137                }
 138
 139                /* Do additive increase */
 140                if (tp->snd_cwnd < tp->snd_cwnd_clamp) {
 141                        /* cwnd = cwnd + a(w) / cwnd */
 142                        tp->snd_cwnd_cnt += ca->ai + 1;
 143                        if (tp->snd_cwnd_cnt >= tp->snd_cwnd) {
 144                                tp->snd_cwnd_cnt -= tp->snd_cwnd;
 145                                tp->snd_cwnd++;
 146                        }
 147                }
 148        }
 149}
 150
 151static u32 hstcp_ssthresh(struct sock *sk)
 152{
 153        const struct tcp_sock *tp = tcp_sk(sk);
 154        const struct hstcp *ca = inet_csk_ca(sk);
 155
 156        /* Do multiplicative decrease */
 157        return max(tp->snd_cwnd - ((tp->snd_cwnd * hstcp_aimd_vals[ca->ai].md) >> 8), 2U);
 158}
 159
 160
 161static struct tcp_congestion_ops tcp_highspeed __read_mostly = {
 162        .init           = hstcp_init,
 163        .ssthresh       = hstcp_ssthresh,
 164        .cong_avoid     = hstcp_cong_avoid,
 165        .min_cwnd       = tcp_reno_min_cwnd,
 166
 167        .owner          = THIS_MODULE,
 168        .name           = "highspeed"
 169};
 170
 171static int __init hstcp_register(void)
 172{
 173        BUILD_BUG_ON(sizeof(struct hstcp) > ICSK_CA_PRIV_SIZE);
 174        return tcp_register_congestion_control(&tcp_highspeed);
 175}
 176
 177static void __exit hstcp_unregister(void)
 178{
 179        tcp_unregister_congestion_control(&tcp_highspeed);
 180}
 181
 182module_init(hstcp_register);
 183module_exit(hstcp_unregister);
 184
 185MODULE_AUTHOR("John Heffner");
 186MODULE_LICENSE("GPL");
 187MODULE_DESCRIPTION("High Speed TCP");
 188
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