net/ipv4/tcp_hybla.c

   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. */
  17 struct 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 */
  28 static int rtt0 = 25;
  29 module_param(rtt0, int, 0644);
  30 MODULE_PARM_DESC(rtt0, "reference rout trip time (ms)");
  31
  32 /* This is called to refresh values for hybla parameters */
  33 static 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
  45 static 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
  67 static 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
  74 static 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  */
  89 static 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
 166 static 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
 177 static 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
 183 static void __exit hybla_unregister(void)
 184 {
 185         tcp_unregister_congestion_control(&tcp_hybla);
 186 }
 187
 188 module_init(hybla_register);
 189 module_exit(hybla_unregister);
 190
 191 MODULE_AUTHOR("Daniele Lacamera");
 192 MODULE_LICENSE("GPL");
 193 MODULE_DESCRIPTION("TCP Hybla");