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/config.h>
  14 #include <linux/module.h>
  15 #include <net/tcp.h>
  16
  17 /* Tcp Hybla structure. */
  18 struct hybla {
  19         u8    hybla_en;
  20         u32   snd_cwnd_cents; /* Keeps increment values when it is <1, <<7 */
  21         u32   rho;            /* Rho parameter, integer part  */
  22         u32   rho2;           /* Rho * Rho, integer part */
  23         u32   rho_3ls;        /* Rho parameter, <<3 */
  24         u32   rho2_7ls;       /* Rho^2, <<7     */
  25         u32   minrtt;         /* Minimum smoothed round trip time value seen */
  26 };
  27
  28 /* Hybla reference round trip time (default= 1/40 sec = 25 ms),
  29    expressed in jiffies */
  30 static int rtt0 = 25;
  31 module_param(rtt0, int, 0644);
  32 MODULE_PARM_DESC(rtt0, "reference rout trip time (ms)");
  33
  34
  35 /* This is called to refresh values for hybla parameters */
  36 static inline void hybla_recalc_param (struct sock *sk)
  37 {
  38         struct hybla *ca = inet_csk_ca(sk);
  39
  40         ca->rho_3ls = max_t(u32, tcp_sk(sk)->srtt / msecs_to_jiffies(rtt0), 8);
  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 = 1;
  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 = tp->srtt;
  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         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 rtt,
  90                             u32 in_flight, int flag)
  91 {
  92         struct tcp_sock *tp = tcp_sk(sk);
  93         struct hybla *ca = inet_csk_ca(sk);
  94         u32 increment, odd, rho_fractions;
  95         int is_slowstart = 0;
  96
  97         /*  Recalculate rho only if this srtt is the lowest */
  98         if (tp->srtt < ca->minrtt){
  99                 hybla_recalc_param(sk);
 100                 ca->minrtt = tp->srtt;
 101         }
 102
 103         if (!tcp_is_cwnd_limited(sk, in_flight))
 104                 return;
 105
 106         if (!ca->hybla_en)
 107                 return tcp_reno_cong_avoid(sk, ack, rtt, in_flight, flag);
 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 << ca->rho) * hybla_fraction(rho_fractions))
 130                         - 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
 154         /* clamp down slowstart cwnd to ssthresh value. */
 155         if (is_slowstart)
 156                 tp->snd_cwnd = min(tp->snd_cwnd, tp->snd_ssthresh);
 157
 158         tp->snd_cwnd = min_t(u32, tp->snd_cwnd, tp->snd_cwnd_clamp);
 159 }
 160
 161 static struct tcp_congestion_ops tcp_hybla = {
 162         .init           = hybla_init,
 163         .ssthresh       = tcp_reno_ssthresh,
 164         .min_cwnd       = tcp_reno_min_cwnd,
 165         .cong_avoid     = hybla_cong_avoid,
 166         .set_state      = hybla_state,
 167
 168         .owner          = THIS_MODULE,
 169         .name           = "hybla"
 170 };
 171
 172 static int __init hybla_register(void)
 173 {
 174         BUG_ON(sizeof(struct hybla) > ICSK_CA_PRIV_SIZE);
 175         return tcp_register_congestion_control(&tcp_hybla);
 176 }
 177
 178 static void __exit hybla_unregister(void)
 179 {
 180         tcp_unregister_congestion_control(&tcp_hybla);
 181 }
 182
 183 module_init(hybla_register);
 184 module_exit(hybla_unregister);
 185
 186 MODULE_AUTHOR("Daniele Lacamera");
 187 MODULE_LICENSE("GPL");
 188 MODULE_DESCRIPTION("TCP Hybla");