[TCP]: Add TCP Hybla congestion control module.

TCP Hybla congestion avoidance.

- "In heterogeneous networks, TCP connections that incorporate a
terrestrial or satellite radio link are greatly disadvantaged with
respect to entirely wired connections, because of their longer round
trip times (RTTs). To cope with this problem, a new TCP proposal, the
TCP Hybla, is presented and discussed in the paper[1]. It stems from an
analytical evaluation of the congestion window dynamics in the TCP
standard versions (Tahoe, Reno, NewReno), which suggests the necessary
modifications to remove the performance dependence on RTT.[...]"[1]

[1]: Carlo Caini, Rosario Firrincieli, "TCP Hybla: a TCP enhancement for
heterogeneous networks",
International Journal of Satellite Communications and Networking
Volume 22, Issue 5 , Pages 547 - 566. September 2004.

Signed-off-by: Daniele Lacamera (root at danielinux.net)net
Signed-off-by: Stephen Hemminger <shemminger@osdl.org>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 187 insertions, 0 deletions

diff --git a/net/ipv4/tcp_hybla.c b/net/ipv4/tcp_hybla.c
new file mode 100644
index 000000000000..13a66342c304
--- /dev/null
+++ b/net/ipv4/tcp_hybla.c
@@ -0,0 +1,187 @@
+/*
+ * 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");