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