[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>

net/ipv4/Kconfig

@@ -478,6 +478,16 @@ config TCP_CONG_HSTCP
 	increase the congestion window by when an ACK is received.
  	For more detail	see http://www.icir.org/floyd/hstcp.html
 
+config TCP_CONG_HYBLA
+	tristate "TCP-Hybla congestion control algorithm"
+	depends on INET && EXPERIMENTAL
+	default n
+	---help---
+	TCP-Hybla is a sender-side only change that eliminates penalization of
+	long-RTT, large-bandwidth connections, like when satellite legs are
+	involved, expecially when sharing a common bottleneck with normal
+	terrestrial connections.
+
 endmenu
 
 source "net/ipv4/ipvs/Kconfig"

net/ipv4/Makefile

@@ -34,6 +34,7 @@ obj-$(CONFIG_IP_ROUTE_MULTIPATH_CACHED) += multipath.o
 obj-$(CONFIG_TCP_CONG_BIC) += tcp_bic.o
 obj-$(CONFIG_TCP_CONG_WESTWOOD) += tcp_westwood.o
 obj-$(CONFIG_TCP_CONG_HSTCP) += tcp_highspeed.o
+obj-$(CONFIG_TCP_CONG_HYBLA) += tcp_hybla.o
 
 obj-$(CONFIG_XFRM) += xfrm4_policy.o xfrm4_state.o xfrm4_input.o \
 		      xfrm4_output.o

net/ipv4/tcp_hybla.c

+/*
+ * 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");