LXR linux/net/ipv4/tcp

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