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        u8    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;         /* Minimum smoothed round trip time value seen */
  25};
  26
  27/* Hybla reference round trip time (default= 1/40 sec = 25 ms),
  28   expressed in jiffies */
  29static int rtt0 = 25;
  30module_param(rtt0, int, 0644);
  31MODULE_PARM_DESC(rtt0, "reference rout trip time (ms)");
  32
  33
  34/* This is called to refresh values for hybla parameters */
  35static inline void hybla_recalc_param (struct sock *sk)
  36{
  37        struct hybla *ca = inet_csk_ca(sk);
  38
  39        ca->rho_3ls = max_t(u32, tcp_sk(sk)->srtt / msecs_to_jiffies(rtt0), 8);
  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 = 1;
  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 = tp->srtt;
  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        ca->hybla_en = (ca_state == TCP_CA_Open);
  71}
  72
  73static inline u32 hybla_fraction(u32 odds)
  74{
  75        static const u32 fractions[] = {
  76                128, 139, 152, 165, 181, 197, 215, 234,
  77        };
  78
  79        return (odds < ARRAY_SIZE(fractions)) ? fractions[odds] : 128;
  80}
  81
  82/* TCP Hybla main routine.
  83 * This is the algorithm behavior:
  84 *     o Recalc Hybla parameters if min_rtt has changed
  85 *     o Give cwnd a new value based on the model proposed
  86 *     o remember increments <1
  87 */
  88static void hybla_cong_avoid(struct sock *sk, u32 ack,
  89                            u32 in_flight, int flag)
  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 < ca->minrtt){
  98                hybla_recalc_param(sk);
  99                ca->minrtt = tp->srtt;
 100        }
 101
 102        if (!tcp_is_cwnd_limited(sk, in_flight))
 103                return;
 104
 105        if (!ca->hybla_en)
 106                return tcp_reno_cong_avoid(sk, ack, in_flight, flag);
 107
 108        if (ca->rho == 0)
 109                hybla_recalc_param(sk);
 110
 111        rho_fractions = ca->rho_3ls - (ca->rho << 3);
 112
 113        if (tp->snd_cwnd < tp->snd_ssthresh) {
 114                /*
 115                 * slow start
 116                 *      INC = 2^RHO - 1
 117                 * This is done by splitting the rho parameter
 118                 * into 2 parts: an integer part and a fraction part.
 119                 * Inrement<<7 is estimated by doing:
 120                 *             [2^(int+fract)]<<7
 121                 * that is equal to:
 122                 *             (2^int)  *  [(2^fract) <<7]
 123                 * 2^int is straightly computed as 1<<int,
 124                 * while we will use hybla_slowstart_fraction_increment() to
 125                 * calculate 2^fract in a <<7 value.
 126                 */
 127                is_slowstart = 1;
 128                increment = ((1 << ca->rho) * hybla_fraction(rho_fractions))
 129                        - 128;
 130        } else {
 131                /*
 132                 * congestion avoidance
 133                 * INC = RHO^2 / W
 134                 * as long as increment is estimated as (rho<<7)/window
 135                 * it already is <<7 and we can easily count its fractions.
 136                 */
 137                increment = ca->rho2_7ls / tp->snd_cwnd;
 138                if (increment < 128)
 139                        tp->snd_cwnd_cnt++;
 140        }
 141
 142        odd = increment % 128;
 143        tp->snd_cwnd += increment >> 7;
 144        ca->snd_cwnd_cents += odd;
 145
 146        /* check when fractions goes >=128 and increase cwnd by 1. */
 147        while (ca->snd_cwnd_cents >= 128) {
 148                tp->snd_cwnd++;
 149                ca->snd_cwnd_cents -= 128;
 150                tp->snd_cwnd_cnt = 0;
 151        }
 152
 153        /* clamp down slowstart cwnd to ssthresh value. */
 154        if (is_slowstart)
 155                tp->snd_cwnd = min(tp->snd_cwnd, tp->snd_ssthresh);
 156
 157        tp->snd_cwnd = min_t(u32, tp->snd_cwnd, tp->snd_cwnd_clamp);
 158}
 159
 160static struct tcp_congestion_ops tcp_hybla = {
 161        .init           = hybla_init,
 162        .ssthresh       = tcp_reno_ssthresh,
 163        .min_cwnd       = tcp_reno_min_cwnd,
 164        .cong_avoid     = hybla_cong_avoid,
 165        .set_state      = hybla_state,
 166
 167        .owner          = THIS_MODULE,
 168        .name           = "hybla"
 169};
 170
 171static int __init hybla_register(void)
 172{
 173        BUILD_BUG_ON(sizeof(struct hybla) > ICSK_CA_PRIV_SIZE);
 174        return tcp_register_congestion_control(&tcp_hybla);
 175}
 176
 177static void __exit hybla_unregister(void)
 178{
 179        tcp_unregister_congestion_control(&tcp_hybla);
 180}
 181
 182module_init(hybla_register);
 183module_exit(hybla_unregister);
 184
 185MODULE_AUTHOR("Daniele Lacamera");
 186MODULE_LICENSE("GPL");
 187MODULE_DESCRIPTION("TCP Hybla");
 188