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
  33 /* This is called to refresh values for hybla parameters */
  34 static 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
  46 static 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
  68 static 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
  75 static 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  */
  90 static void hybla_cong_avoid(struct sock *sk, u32 ack, u32 acked,
  91                              u32 in_flight)
  92 {
  93         struct tcp_sock *tp = tcp_sk(sk);
  94         struct hybla *ca = inet_csk_ca(sk);
  95         u32 increment, odd, rho_fractions;
  96         int is_slowstart = 0;
  97
  98         /*  Recalculate rho only if this srtt is the lowest */
  99         if (tp->srtt_us < ca->minrtt_us) {
 100                 hybla_recalc_param(sk);
 101                 ca->minrtt_us = tp->srtt_us;
 102         }
 103
 104         if (!tcp_is_cwnd_limited(sk, in_flight))
 105                 return;
 106
 107         if (!ca->hybla_en) {
 108                 tcp_reno_cong_avoid(sk, ack, acked, in_flight);
 109                 return;
 110         }
 111
 112         if (ca->rho == 0)
 113                 hybla_recalc_param(sk);
 114
 115         rho_fractions = ca->rho_3ls - (ca->rho << 3);
 116
 117         if (tp->snd_cwnd < tp->snd_ssthresh) {
 118                 /*
 119                  * slow start
 120                  *      INC = 2^RHO - 1
 121                  * This is done by splitting the rho parameter
 122                  * into 2 parts: an integer part and a fraction part.
 123                  * Inrement<<7 is estimated by doing:
 124                  *             [2^(int+fract)]<<7
 125                  * that is equal to:
 126                  *             (2^int)  *  [(2^fract) <<7]
 127                  * 2^int is straightly computed as 1<<int,
 128                  * while we will use hybla_slowstart_fraction_increment() to
 129                  * calculate 2^fract in a <<7 value.
 130                  */
 131                 is_slowstart = 1;
 132                 increment = ((1 << min(ca->rho, 16U)) *
 133                         hybla_fraction(rho_fractions)) - 128;
 134         } else {
 135                 /*
 136                  * congestion avoidance
 137                  * INC = RHO^2 / W
 138                  * as long as increment is estimated as (rho<<7)/window
 139                  * it already is <<7 and we can easily count its fractions.
 140                  */
 141                 increment = ca->rho2_7ls / tp->snd_cwnd;
 142                 if (increment < 128)
 143                         tp->snd_cwnd_cnt++;
 144         }
 145
 146         odd = increment % 128;
 147         tp->snd_cwnd += increment >> 7;
 148         ca->snd_cwnd_cents += odd;
 149
 150         /* check when fractions goes >=128 and increase cwnd by 1. */
 151         while (ca->snd_cwnd_cents >= 128) {
 152                 tp->snd_cwnd++;
 153                 ca->snd_cwnd_cents -= 128;
 154                 tp->snd_cwnd_cnt = 0;
 155         }
 156         /* check when cwnd has not been incremented for a while */
 157         if (increment == 0 && odd == 0 && tp->snd_cwnd_cnt >= tp->snd_cwnd) {
 158                 tp->snd_cwnd++;
 159                 tp->snd_cwnd_cnt = 0;
 160         }
 161         /* clamp down slowstart cwnd to ssthresh value. */
 162         if (is_slowstart)
 163                 tp->snd_cwnd = min(tp->snd_cwnd, tp->snd_ssthresh);
 164
 165         tp->snd_cwnd = min_t(u32, tp->snd_cwnd, tp->snd_cwnd_clamp);
 166 }
 167
 168 static struct tcp_congestion_ops tcp_hybla __read_mostly = {
 169         .init           = hybla_init,
 170         .ssthresh       = tcp_reno_ssthresh,
 171         .cong_avoid     = hybla_cong_avoid,
 172         .set_state      = hybla_state,
 173
 174         .owner          = THIS_MODULE,
 175         .name           = "hybla"
 176 };
 177
 178 static 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
 184 static void __exit hybla_unregister(void)
 185 {
 186         tcp_unregister_congestion_control(&tcp_hybla);
 187 }
 188
 189 module_init(hybla_register);
 190 module_exit(hybla_unregister);
 191
 192 MODULE_AUTHOR("Daniele Lacamera");
 193 MODULE_LICENSE("GPL");
 194 MODULE_DESCRIPTION("TCP Hybla");