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         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 */
  29 static int rtt0 = 25;
  30 module_param(rtt0, int, 0644);
  31 MODULE_PARM_DESC(rtt0, "reference rout trip time (ms)");
  32
  33
  34 /* This is called to refresh values for hybla parameters */
  35 static 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
  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 = 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
  67 static 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
  73 static 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  */
  88 static 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
 165 static struct tcp_congestion_ops tcp_hybla = {
 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
 176 static 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
 182 static void __exit hybla_unregister(void)
 183 {
 184         tcp_unregister_congestion_control(&tcp_hybla);
 185 }
 186
 187 module_init(hybla_register);
 188 module_exit(hybla_unregister);
 189
 190 MODULE_AUTHOR("Daniele Lacamera");
 191 MODULE_LICENSE("GPL");
 192 MODULE_DESCRIPTION("TCP Hybla");