LXR linux/net/ipv4/tcp

   1// SPDX-License-Identifier: GPL-2.0-only
   2/*
   3 * TCP HYBLA
   4 *
   5 * TCP-HYBLA Congestion control algorithm, based on:
   6 *   C.Caini, R.Firrincieli, "TCP-Hybla: A TCP Enhancement
   7 *   for Heterogeneous Networks",
   8 *   International Journal on satellite Communications,
   9 *                                     September 2004
  10 *    Daniele Lacamera
  11 *    root at danielinux.net
  12 */
  13
  14#include <linux/module.h>
  15#include <net/tcp.h>
  16
  17/* Tcp Hybla structure. */
  18struct hybla {
  19        bool  hybla_en;
  20        u32   snd_cwnd_cents; /* Keeps increment values when it is <1, <<7 */
  21        u32   rho;            /* Rho parameter, integer part  */
  22        u32   rho2;           /* Rho * Rho, integer part */
  23        u32   rho_3ls;        /* Rho parameter, <<3 */
  24        u32   rho2_7ls;       /* Rho^2, <<7     */
  25        u32   minrtt_us;      /* Minimum smoothed round trip time value seen */
  26};
  27
  28/* Hybla reference round trip time (default= 1/40 sec = 25 ms), in ms */
  29static int rtt0 = 25;
  30module_param(rtt0, int, 0644);
  31MODULE_PARM_DESC(rtt0, "reference rout trip time (ms)");
  32
  33/* This is called to refresh values for hybla parameters */
  34static inline void hybla_recalc_param (struct sock *sk)
  35{
  36        struct hybla *ca = inet_csk_ca(sk);
  37
  38        ca->rho_3ls = max_t(u32,
  39                            tcp_sk(sk)->srtt_us / (rtt0 * USEC_PER_MSEC),
  40                            8U);
  41        ca->rho = ca->rho_3ls >> 3;
  42        ca->rho2_7ls = (ca->rho_3ls * ca->rho_3ls) << 1;
  43        ca->rho2 = ca->rho2_7ls >> 7;
  44}
  45
  46static void hybla_init(struct sock *sk)
  47{
  48        struct tcp_sock *tp = tcp_sk(sk);
  49        struct hybla *ca = inet_csk_ca(sk);
  50
  51        ca->rho = 0;
  52        ca->rho2 = 0;
  53        ca->rho_3ls = 0;
  54        ca->rho2_7ls = 0;
  55        ca->snd_cwnd_cents = 0;
  56        ca->hybla_en = true;
  57        tp->snd_cwnd = 2;
  58        tp->snd_cwnd_clamp = 65535;
  59
  60        /* 1st Rho measurement based on initial srtt */
  61        hybla_recalc_param(sk);
  62
  63        /* set minimum rtt as this is the 1st ever seen */
  64        ca->minrtt_us = tp->srtt_us;
  65        tp->snd_cwnd = ca->rho;
  66}
  67
  68static void hybla_state(struct sock *sk, u8 ca_state)
  69{
  70        struct hybla *ca = inet_csk_ca(sk);
  71
  72        ca->hybla_en = (ca_state == TCP_CA_Open);
  73}
  74
  75static inline u32 hybla_fraction(u32 odds)
  76{
  77        static const u32 fractions[] = {
  78                128, 139, 152, 165, 181, 197, 215, 234,
  79        };
  80
  81        return (odds < ARRAY_SIZE(fractions)) ? fractions[odds] : 128;
  82}
  83
  84/* TCP Hybla main routine.
  85 * This is the algorithm behavior:
  86 *     o Recalc Hybla parameters if min_rtt has changed
  87 *     o Give cwnd a new value based on the model proposed
  88 *     o remember increments <1
  89 */
  90static void hybla_cong_avoid(struct sock *sk, u32 ack, u32 acked)
  91{
  92        struct tcp_sock *tp = tcp_sk(sk);
  93        struct hybla *ca = inet_csk_ca(sk);
  94        u32 increment, odd, rho_fractions;
  95        int is_slowstart = 0;
  96
  97        /*  Recalculate rho only if this srtt is the lowest */
  98        if (tp->srtt_us < ca->minrtt_us) {
  99                hybla_recalc_param(sk);
 100                ca->minrtt_us = tp->srtt_us;
 101        }
 102
 103        if (!tcp_is_cwnd_limited(sk))
 104                return;
 105
 106        if (!ca->hybla_en) {
 107                tcp_reno_cong_avoid(sk, ack, acked);
 108                return;
 109        }
 110
 111        if (ca->rho == 0)
 112                hybla_recalc_param(sk);
 113
 114        rho_fractions = ca->rho_3ls - (ca->rho << 3);
 115
 116        if (tcp_in_slow_start(tp)) {
 117                /*
 118                 * slow start
 119                 *      INC = 2^RHO - 1
 120                 * This is done by splitting the rho parameter
 121                 * into 2 parts: an integer part and a fraction part.
 122                 * Inrement<<7 is estimated by doing:
 123                 *             [2^(int+fract)]<<7
 124                 * that is equal to:
 125                 *             (2^int)  *  [(2^fract) <<7]
 126                 * 2^int is straightly computed as 1<<int,
 127                 * while we will use hybla_slowstart_fraction_increment() to
 128                 * calculate 2^fract in a <<7 value.
 129                 */
 130                is_slowstart = 1;
 131                increment = ((1 << min(ca->rho, 16U)) *
 132                        hybla_fraction(rho_fractions)) - 128;
 133        } else {
 134                /*
 135                 * congestion avoidance
 136                 * INC = RHO^2 / W
 137                 * as long as increment is estimated as (rho<<7)/window
 138                 * it already is <<7 and we can easily count its fractions.
 139                 */
 140                increment = ca->rho2_7ls / tp->snd_cwnd;
 141                if (increment < 128)
 142                        tp->snd_cwnd_cnt++;
 143        }
 144
 145        odd = increment % 128;
 146        tp->snd_cwnd += increment >> 7;
 147        ca->snd_cwnd_cents += odd;
 148
 149        /* check when fractions goes >=128 and increase cwnd by 1. */
 150        while (ca->snd_cwnd_cents >= 128) {
 151                tp->snd_cwnd++;
 152                ca->snd_cwnd_cents -= 128;
 153                tp->snd_cwnd_cnt = 0;
 154        }
 155        /* check when cwnd has not been incremented for a while */
 156        if (increment == 0 && odd == 0 && tp->snd_cwnd_cnt >= tp->snd_cwnd) {
 157                tp->snd_cwnd++;
 158                tp->snd_cwnd_cnt = 0;
 159        }
 160        /* clamp down slowstart cwnd to ssthresh value. */
 161        if (is_slowstart)
 162                tp->snd_cwnd = min(tp->snd_cwnd, tp->snd_ssthresh);
 163
 164        tp->snd_cwnd = min_t(u32, tp->snd_cwnd, tp->snd_cwnd_clamp);
 165}
 166
 167static struct tcp_congestion_ops tcp_hybla __read_mostly = {
 168        .init           = hybla_init,
 169        .ssthresh       = tcp_reno_ssthresh,
 170        .undo_cwnd      = tcp_reno_undo_cwnd,
 171        .cong_avoid     = hybla_cong_avoid,
 172        .set_state      = hybla_state,
 173
 174        .owner          = THIS_MODULE,
 175        .name           = "hybla"
 176};
 177
 178static int __init hybla_register(void)
 179{
 180        BUILD_BUG_ON(sizeof(struct hybla) > ICSK_CA_PRIV_SIZE);
 181        return tcp_register_congestion_control(&tcp_hybla);
 182}
 183
 184static void __exit hybla_unregister(void)
 185{
 186        tcp_unregister_congestion_control(&tcp_hybla);
 187}
 188
 189module_init(hybla_register);
 190module_exit(hybla_unregister);
 191
 192MODULE_AUTHOR("Daniele Lacamera");
 193MODULE_LICENSE("GPL");
 194MODULE_DESCRIPTION("TCP Hybla");
 195