linux/net/ipv4/tcp_highspeed.c
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   1// SPDX-License-Identifier: GPL-2.0-only
   2/*
   3 * Sally Floyd's High Speed TCP (RFC 3649) congestion control
   4 *
   5 * See http://www.icir.org/floyd/hstcp.html
   6 *
   7 * John Heffner <jheffner@psc.edu>
   8 */
   9
  10#include <linux/module.h>
  11#include <net/tcp.h>
  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 ack, u32 acked)
 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))
 118                return;
 119
 120        if (tcp_in_slow_start(tp))
 121                tcp_slow_start(tp, acked);
 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        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
 160static struct tcp_congestion_ops tcp_highspeed __read_mostly = {
 161        .init           = hstcp_init,
 162        .ssthresh       = hstcp_ssthresh,
 163        .undo_cwnd      = tcp_reno_undo_cwnd,
 164        .cong_avoid     = hstcp_cong_avoid,
 165
 166        .owner          = THIS_MODULE,
 167        .name           = "highspeed"
 168};
 169
 170static int __init hstcp_register(void)
 171{
 172        BUILD_BUG_ON(sizeof(struct hstcp) > ICSK_CA_PRIV_SIZE);
 173        return tcp_register_congestion_control(&tcp_highspeed);
 174}
 175
 176static void __exit hstcp_unregister(void)
 177{
 178        tcp_unregister_congestion_control(&tcp_highspeed);
 179}
 180
 181module_init(hstcp_register);
 182module_exit(hstcp_unregister);
 183
 184MODULE_AUTHOR("John Heffner");
 185MODULE_LICENSE("GPL");
 186MODULE_DESCRIPTION("High Speed TCP");
 187