linux/net/ipv4/tcp_hybla.c
<<
>>
Prefs
   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;         /* 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
  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, tcp_sk(sk)->srtt / msecs_to_jiffies(rtt0), 8);
  39        ca->rho = ca->rho_3ls >> 3;
  40        ca->rho2_7ls = (ca->rho_3ls * ca->rho_3ls) << 1;
  41        ca->rho2 = ca->rho2_7ls >> 7;
  42}
  43
  44static void hybla_init(struct sock *sk)
  45{
  46        struct tcp_sock *tp = tcp_sk(sk);
  47        struct hybla *ca = inet_csk_ca(sk);
  48
  49        ca->rho = 0;
  50        ca->rho2 = 0;
  51        ca->rho_3ls = 0;
  52        ca->rho2_7ls = 0;
  53        ca->snd_cwnd_cents = 0;
  54        ca->hybla_en = true;
  55        tp->snd_cwnd = 2;
  56        tp->snd_cwnd_clamp = 65535;
  57
  58        /* 1st Rho measurement based on initial srtt */
  59        hybla_recalc_param(sk);
  60
  61        /* set minimum rtt as this is the 1st ever seen */
  62        ca->minrtt = tp->srtt;
  63        tp->snd_cwnd = ca->rho;
  64}
  65
  66static void hybla_state(struct sock *sk, u8 ca_state)
  67{
  68        struct hybla *ca = inet_csk_ca(sk);
  69
  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, u32 in_flight)
  89{
  90        struct tcp_sock *tp = tcp_sk(sk);
  91        struct hybla *ca = inet_csk_ca(sk);
  92        u32 increment, odd, rho_fractions;
  93        int is_slowstart = 0;
  94
  95        /*  Recalculate rho only if this srtt is the lowest */
  96        if (tp->srtt < ca->minrtt){
  97                hybla_recalc_param(sk);
  98                ca->minrtt = tp->srtt;
  99        }
 100
 101        if (!tcp_is_cwnd_limited(sk, in_flight))
 102                return;
 103
 104        if (!ca->hybla_en) {
 105                tcp_reno_cong_avoid(sk, ack, in_flight);
 106                return;
 107        }
 108
 109        if (ca->rho == 0)
 110                hybla_recalc_param(sk);
 111
 112        rho_fractions = ca->rho_3ls - (ca->rho << 3);
 113
 114        if (tp->snd_cwnd < tp->snd_ssthresh) {
 115                /*
 116                 * slow start
 117                 *      INC = 2^RHO - 1
 118                 * This is done by splitting the rho parameter
 119                 * into 2 parts: an integer part and a fraction part.
 120                 * Inrement<<7 is estimated by doing:
 121                 *             [2^(int+fract)]<<7
 122                 * that is equal to:
 123                 *             (2^int)  *  [(2^fract) <<7]
 124                 * 2^int is straightly computed as 1<<int,
 125                 * while we will use hybla_slowstart_fraction_increment() to
 126                 * calculate 2^fract in a <<7 value.
 127                 */
 128                is_slowstart = 1;
 129                increment = ((1 << min(ca->rho, 16U)) *
 130                        hybla_fraction(rho_fractions)) - 128;
 131        } else {
 132                /*
 133                 * congestion avoidance
 134                 * INC = RHO^2 / W
 135                 * as long as increment is estimated as (rho<<7)/window
 136                 * it already is <<7 and we can easily count its fractions.
 137                 */
 138                increment = ca->rho2_7ls / tp->snd_cwnd;
 139                if (increment < 128)
 140                        tp->snd_cwnd_cnt++;
 141        }
 142
 143        odd = increment % 128;
 144        tp->snd_cwnd += increment >> 7;
 145        ca->snd_cwnd_cents += odd;
 146
 147        /* check when fractions goes >=128 and increase cwnd by 1. */
 148        while (ca->snd_cwnd_cents >= 128) {
 149                tp->snd_cwnd++;
 150                ca->snd_cwnd_cents -= 128;
 151                tp->snd_cwnd_cnt = 0;
 152        }
 153        /* check when cwnd has not been incremented for a while */
 154        if (increment == 0 && odd == 0 && tp->snd_cwnd_cnt >= tp->snd_cwnd) {
 155                tp->snd_cwnd++;
 156                tp->snd_cwnd_cnt = 0;
 157        }
 158        /* clamp down slowstart cwnd to ssthresh value. */
 159        if (is_slowstart)
 160                tp->snd_cwnd = min(tp->snd_cwnd, tp->snd_ssthresh);
 161
 162        tp->snd_cwnd = min_t(u32, tp->snd_cwnd, tp->snd_cwnd_clamp);
 163}
 164
 165static struct tcp_congestion_ops tcp_hybla __read_mostly = {
 166        .init           = hybla_init,
 167        .ssthresh       = tcp_reno_ssthresh,
 168        .min_cwnd       = tcp_reno_min_cwnd,
 169        .cong_avoid     = hybla_cong_avoid,
 170        .set_state      = hybla_state,
 171
 172        .owner          = THIS_MODULE,
 173        .name           = "hybla"
 174};
 175
 176static int __init hybla_register(void)
 177{
 178        BUILD_BUG_ON(sizeof(struct hybla) > ICSK_CA_PRIV_SIZE);
 179        return tcp_register_congestion_control(&tcp_hybla);
 180}
 181
 182static void __exit hybla_unregister(void)
 183{
 184        tcp_unregister_congestion_control(&tcp_hybla);
 185}
 186
 187module_init(hybla_register);
 188module_exit(hybla_unregister);
 189
 190MODULE_AUTHOR("Daniele Lacamera");
 191MODULE_LICENSE("GPL");
 192MODULE_DESCRIPTION("TCP Hybla");
 193
lxr.linux.no kindly hosted by Redpill Linpro AS, provider of Linux consulting and operations services since 1995.