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+/*
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+ * TCP HYBLA
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+ *
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+ * TCP-HYBLA Congestion control algorithm, based on:
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+ * C.Caini, R.Firrincieli, "TCP-Hybla: A TCP Enhancement
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+ * for Heterogeneous Networks",
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+ * International Journal on satellite Communications,
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+ * September 2004
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+ * Daniele Lacamera
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+ * root at danielinux.net
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+ */
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+
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+#include <linux/config.h>
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+#include <linux/module.h>
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+#include <net/tcp.h>
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+
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+/* Tcp Hybla structure. */
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+struct hybla {
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+ u8 hybla_en;
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+ u32 snd_cwnd_cents; /* Keeps increment values when it is <1, <<7 */
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+ u32 rho; /* Rho parameter, integer part */
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+ u32 rho2; /* Rho * Rho, integer part */
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+ u32 rho_3ls; /* Rho parameter, <<3 */
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+ u32 rho2_7ls; /* Rho^2, <<7 */
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+ u32 minrtt; /* Minimum smoothed round trip time value seen */
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+};
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+
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+/* Hybla reference round trip time (default= 1/40 sec = 25 ms),
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+ expressed in jiffies */
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+static int rtt0 = 25;
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+module_param(rtt0, int, 0644);
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+MODULE_PARM_DESC(rtt0, "reference rout trip time (ms)");
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+
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+
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+/* This is called to refresh values for hybla parameters */
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+static inline void hybla_recalc_param (struct tcp_sock *tp)
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+{
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+ struct hybla *ca = tcp_ca(tp);
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+
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+ ca->rho_3ls = max_t(u32, tp->srtt / msecs_to_jiffies(rtt0), 8);
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+ ca->rho = ca->rho_3ls >> 3;
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+ ca->rho2_7ls = (ca->rho_3ls * ca->rho_3ls) << 1;
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+ ca->rho2 = ca->rho2_7ls >>7;
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+}
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+
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+static void hybla_init(struct tcp_sock *tp)
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+{
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+ struct hybla *ca = tcp_ca(tp);
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+
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+ ca->rho = 0;
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+ ca->rho2 = 0;
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+ ca->rho_3ls = 0;
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+ ca->rho2_7ls = 0;
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+ ca->snd_cwnd_cents = 0;
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+ ca->hybla_en = 1;
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+ tp->snd_cwnd = 2;
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+ tp->snd_cwnd_clamp = 65535;
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+
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+ /* 1st Rho measurement based on initial srtt */
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+ hybla_recalc_param(tp);
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+
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+ /* set minimum rtt as this is the 1st ever seen */
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+ ca->minrtt = tp->srtt;
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+ tp->snd_cwnd = ca->rho;
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+}
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+
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+static void hybla_state(struct tcp_sock *tp, u8 ca_state)
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+{
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+ struct hybla *ca = tcp_ca(tp);
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+
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+ ca->hybla_en = (ca_state == TCP_CA_Open);
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+}
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+
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+static inline u32 hybla_fraction(u32 odds)
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+{
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+ static const u32 fractions[] = {
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+ 128, 139, 152, 165, 181, 197, 215, 234,
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+ };
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+
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+ return (odds < ARRAY_SIZE(fractions)) ? fractions[odds] : 128;
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+}
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+
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+/* TCP Hybla main routine.
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+ * This is the algorithm behavior:
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+ * o Recalc Hybla parameters if min_rtt has changed
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+ * o Give cwnd a new value based on the model proposed
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+ * o remember increments <1
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+ */
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+static void hybla_cong_avoid(struct tcp_sock *tp, u32 ack, u32 rtt,
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+ u32 in_flight, int flag)
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+{
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+ struct hybla *ca = tcp_ca(tp);
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+ u32 increment, odd, rho_fractions;
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+ int is_slowstart = 0;
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+
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+ /* Recalculate rho only if this srtt is the lowest */
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+ if (tp->srtt < ca->minrtt){
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+ hybla_recalc_param(tp);
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+ ca->minrtt = tp->srtt;
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+ }
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+
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+ if (!ca->hybla_en)
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+ return tcp_reno_cong_avoid(tp, ack, rtt, in_flight, flag);
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+
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+ if (in_flight < tp->snd_cwnd)
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+ return;
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+
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+ if (ca->rho == 0)
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+ hybla_recalc_param(tp);
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+
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+ rho_fractions = ca->rho_3ls - (ca->rho << 3);
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+
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+ if (tp->snd_cwnd < tp->snd_ssthresh) {
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+ /*
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+ * slow start
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+ * INC = 2^RHO - 1
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+ * This is done by splitting the rho parameter
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+ * into 2 parts: an integer part and a fraction part.
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+ * Inrement<<7 is estimated by doing:
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+ * [2^(int+fract)]<<7
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+ * that is equal to:
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+ * (2^int) * [(2^fract) <<7]
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+ * 2^int is straightly computed as 1<<int,
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+ * while we will use hybla_slowstart_fraction_increment() to
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+ * calculate 2^fract in a <<7 value.
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+ */
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+ is_slowstart = 1;
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+ increment = ((1 << ca->rho) * hybla_fraction(rho_fractions))
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+ - 128;
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+ } else {
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+ /*
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+ * congestion avoidance
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+ * INC = RHO^2 / W
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+ * as long as increment is estimated as (rho<<7)/window
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+ * it already is <<7 and we can easily count its fractions.
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+ */
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+ increment = ca->rho2_7ls / tp->snd_cwnd;
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+ if (increment < 128)
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+ tp->snd_cwnd_cnt++;
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+ }
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+
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+ odd = increment % 128;
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+ tp->snd_cwnd += increment >> 7;
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+ ca->snd_cwnd_cents += odd;
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+
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+ /* check when fractions goes >=128 and increase cwnd by 1. */
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+ while(ca->snd_cwnd_cents >= 128) {
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+ tp->snd_cwnd++;
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+ ca->snd_cwnd_cents -= 128;
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+ tp->snd_cwnd_cnt = 0;
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+ }
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+
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+ /* clamp down slowstart cwnd to ssthresh value. */
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+ if (is_slowstart)
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+ tp->snd_cwnd = min(tp->snd_cwnd, tp->snd_ssthresh);
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+
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+ tp->snd_cwnd = min_t(u32, tp->snd_cwnd, tp->snd_cwnd_clamp);
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+}
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+
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+static struct tcp_congestion_ops tcp_hybla = {
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+ .init = hybla_init,
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+ .ssthresh = tcp_reno_ssthresh,
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+ .min_cwnd = tcp_reno_min_cwnd,
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+ .cong_avoid = hybla_cong_avoid,
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+ .set_state = hybla_state,
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+
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+ .owner = THIS_MODULE,
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+ .name = "hybla"
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+};
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+
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+static int __init hybla_register(void)
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+{
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+ BUG_ON(sizeof(struct hybla) > TCP_CA_PRIV_SIZE);
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+ return tcp_register_congestion_control(&tcp_hybla);
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+}
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+
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+static void __exit hybla_unregister(void)
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+{
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+ tcp_unregister_congestion_control(&tcp_hybla);
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+}
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+
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+module_init(hybla_register);
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+module_exit(hybla_unregister);
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+
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+MODULE_AUTHOR("Daniele Lacamera");
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+MODULE_LICENSE("GPL");
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+MODULE_DESCRIPTION("TCP Hybla");
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