[TCP]: Add TCP Westwood congestion control module.

This is the existing 2.6.12 Westwood code moved from tcp_input
to the new congestion framework. A lot of the inline functions
have been eliminated to try and make it clearer.
Signed-off-by: Stephen Hemminger <shemminger@osdl.org>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/ipv4/Kconfig

@@ -452,6 +452,21 @@ config TCP_CONG_BIC
 	increase provides TCP friendliness.
 	See http://www.csc.ncsu.edu/faculty/rhee/export/bitcp/
 
+config TCP_CONG_WESTWOOD
+	tristate "TCP Westwood+"
+	depends on INET
+	default m
+	---help---
+	TCP Westwood+ is a sender-side only modification of the TCP Reno
+	protocol stack that optimizes the performance of TCP congestion
+	control. It is based on end-to-end bandwidth estimation to set
+	congestion window and slow start threshold after a congestion
+	episode. Using this estimation, TCP Westwood+ adaptively sets a
+	slow start threshold and a congestion window which takes into
+	account the bandwidth used  at the time congestion is experienced.
+	TCP Westwood+ significantly increases fairness wrt TCP Reno in
+	wired networks and throughput over wireless links.
+
 endmenu
 
 source "net/ipv4/ipvs/Kconfig"

net/ipv4/Makefile

@@ -32,6 +32,7 @@ obj-$(CONFIG_IP_VS) += ipvs/
 obj-$(CONFIG_IP_TCPDIAG) += tcp_diag.o 
 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_XFRM) += xfrm4_policy.o xfrm4_state.o xfrm4_input.o \
 		      xfrm4_output.o

net/ipv4/tcp_westwood.c

+/*
+ * TCP Westwood+
+ *
+ *	Angelo Dell'Aera:	TCP Westwood+ support
+ */
+
+#include <linux/config.h>
+#include <linux/mm.h>
+#include <linux/module.h>
+#include <linux/skbuff.h>
+#include <linux/tcp_diag.h>
+#include <net/tcp.h>
+
+/* TCP Westwood structure */
+struct westwood {
+	u32    bw_ns_est;        /* first bandwidth estimation..not too smoothed 8) */
+	u32    bw_est;           /* bandwidth estimate */
+	u32    rtt_win_sx;       /* here starts a new evaluation... */
+	u32    bk;
+	u32    snd_una;          /* used for evaluating the number of acked bytes */
+	u32    cumul_ack;
+	u32    accounted;
+	u32    rtt;
+	u32    rtt_min;          /* minimum observed RTT */
+};
+
+
+/* TCP Westwood functions and constants */
+#define TCP_WESTWOOD_RTT_MIN   (HZ/20)	/* 50ms */
+#define TCP_WESTWOOD_INIT_RTT  (20*HZ)	/* maybe too conservative?! */
+
+/*
+ * @tcp_westwood_create
+ * This function initializes fields used in TCP Westwood+,
+ * it is called after the initial SYN, so the sequence numbers
+ * are correct but new passive connections we have no
+ * information about RTTmin at this time so we simply set it to
+ * TCP_WESTWOOD_INIT_RTT. This value was chosen to be too conservative
+ * since in this way we're sure it will be updated in a consistent
+ * way as soon as possible. It will reasonably happen within the first
+ * RTT period of the connection lifetime.
+ */
+static void tcp_westwood_init(struct tcp_sock *tp)
+{
+	struct westwood *w = tcp_ca(tp);
+
+	w->bk = 0;
+        w->bw_ns_est = 0;
+        w->bw_est = 0;
+        w->accounted = 0;
+        w->cumul_ack = 0;
+	w->rtt_min = w->rtt = TCP_WESTWOOD_INIT_RTT;
+	w->rtt_win_sx = tcp_time_stamp;
+	w->snd_una = tp->snd_una;
+}
+
+/*
+ * @westwood_do_filter
+ * Low-pass filter. Implemented using constant coefficients.
+ */
+static inline u32 westwood_do_filter(u32 a, u32 b)
+{
+	return (((7 * a) + b) >> 3);
+}
+
+static inline void westwood_filter(struct westwood *w, u32 delta)
+{
+	w->bw_ns_est = westwood_do_filter(w->bw_ns_est, w->bk / delta);
+	w->bw_est = westwood_do_filter(w->bw_est, w->bw_ns_est);
+}
+
+/*
+ * @westwood_pkts_acked
+ * Called after processing group of packets.
+ * but all westwood needs is the last sample of srtt.
+ */
+static void tcp_westwood_pkts_acked(struct tcp_sock *tp, u32 cnt)
+{
+	struct westwood *w = tcp_ca(tp);
+	if (cnt > 0)
+		w->rtt = tp->srtt >> 3;
+}
+
+/*
+ * @westwood_update_window
+ * It updates RTT evaluation window if it is the right moment to do
+ * it. If so it calls filter for evaluating bandwidth.
+ */
+static void westwood_update_window(struct tcp_sock *tp)
+{
+	struct westwood *w = tcp_ca(tp);
+	s32 delta = tcp_time_stamp - w->rtt_win_sx;
+
+	/*
+	 * See if a RTT-window has passed.
+	 * Be careful since if RTT is less than
+	 * 50ms we don't filter but we continue 'building the sample'.
+	 * This minimum limit was chosen since an estimation on small
+	 * time intervals is better to avoid...
+	 * Obviously on a LAN we reasonably will always have
+	 * right_bound = left_bound + WESTWOOD_RTT_MIN
+	 */
+	if (w->rtt && delta > max_t(u32, w->rtt, TCP_WESTWOOD_RTT_MIN)) {
+		westwood_filter(w, delta);
+
+		w->bk = 0;
+		w->rtt_win_sx = tcp_time_stamp;
+	}
+}
+
+/*
+ * @westwood_fast_bw
+ * It is called when we are in fast path. In particular it is called when
+ * header prediction is successful. In such case in fact update is
+ * straight forward and doesn't need any particular care.
+ */
+static inline void westwood_fast_bw(struct tcp_sock *tp)
+{
+	struct westwood *w = tcp_ca(tp);
+
+	westwood_update_window(tp);
+
+	w->bk += tp->snd_una - w->snd_una;
+	w->snd_una = tp->snd_una;
+	w->rtt_min = min(w->rtt, w->rtt_min);
+}
+
+/*
+ * @westwood_acked_count
+ * This function evaluates cumul_ack for evaluating bk in case of
+ * delayed or partial acks.
+ */
+static inline u32 westwood_acked_count(struct tcp_sock *tp)
+{
+	struct westwood *w = tcp_ca(tp);
+
+	w->cumul_ack = tp->snd_una - w->snd_una;
+
+        /* If cumul_ack is 0 this is a dupack since it's not moving
+         * tp->snd_una.
+         */
+        if (!w->cumul_ack) {
+		w->accounted += tp->mss_cache;
+		w->cumul_ack = tp->mss_cache;
+	}
+
+        if (w->cumul_ack > tp->mss_cache) {
+		/* Partial or delayed ack */
+		if (w->accounted >= w->cumul_ack) {
+			w->accounted -= w->cumul_ack;
+			w->cumul_ack = tp->mss_cache;
+		} else {
+			w->cumul_ack -= w->accounted;
+			w->accounted = 0;
+		}
+	}
+
+	w->snd_una = tp->snd_una;
+
+	return w->cumul_ack;
+}
+
+static inline u32 westwood_bw_rttmin(const struct tcp_sock *tp)
+{
+	struct westwood *w = tcp_ca(tp);
+	return max_t(u32, (w->bw_est * w->rtt_min) / tp->mss_cache, 2);
+}
+
+/*
+ * TCP Westwood
+ * Here limit is evaluated as Bw estimation*RTTmin (for obtaining it
+ * in packets we use mss_cache). Rttmin is guaranteed to be >= 2
+ * so avoids ever returning 0.
+ */
+static u32 tcp_westwood_cwnd_min(struct tcp_sock *tp)
+{
+	return westwood_bw_rttmin(tp);
+}
+
+static void tcp_westwood_event(struct tcp_sock *tp, enum tcp_ca_event event)
+{
+	struct westwood *w = tcp_ca(tp);
+
+	switch(event) {
+	case CA_EVENT_FAST_ACK:
+		westwood_fast_bw(tp);
+		break;
+
+	case CA_EVENT_COMPLETE_CWR:
+		tp->snd_cwnd = tp->snd_ssthresh = westwood_bw_rttmin(tp);
+		break;
+
+	case CA_EVENT_FRTO:
+		tp->snd_ssthresh = westwood_bw_rttmin(tp);
+		break;
+
+	case CA_EVENT_SLOW_ACK:
+		westwood_update_window(tp);
+		w->bk += westwood_acked_count(tp);
+		w->rtt_min = min(w->rtt, w->rtt_min);
+		break;
+
+	default:
+		/* don't care */
+		break;
+	}
+}
+
+
+/* Extract info for Tcp socket info provided via netlink. */
+static void tcp_westwood_info(struct tcp_sock *tp, u32 ext,
+			      struct sk_buff *skb)
+{
+	const struct westwood *ca = tcp_ca(tp);
+	if (ext & (1<<(TCPDIAG_VEGASINFO-1))) {
+		struct rtattr *rta;
+		struct tcpvegas_info *info;
+
+		rta = __RTA_PUT(skb, TCPDIAG_VEGASINFO, sizeof(*info));
+		info = RTA_DATA(rta);
+		info->tcpv_enabled = 1;
+		info->tcpv_rttcnt = 0;
+		info->tcpv_rtt = jiffies_to_usecs(ca->rtt);
+		info->tcpv_minrtt = jiffies_to_usecs(ca->rtt_min);
+	rtattr_failure:	;
+	}
+}
+
+
+static struct tcp_congestion_ops tcp_westwood = {
+	.init		= tcp_westwood_init,
+	.ssthresh	= tcp_reno_ssthresh,
+	.cong_avoid	= tcp_reno_cong_avoid,
+	.min_cwnd	= tcp_westwood_cwnd_min,
+	.cwnd_event	= tcp_westwood_event,
+	.get_info	= tcp_westwood_info,
+	.pkts_acked	= tcp_westwood_pkts_acked,
+
+	.owner		= THIS_MODULE,
+	.name		= "westwood"
+};
+
+static int __init tcp_westwood_register(void)
+{
+	BUG_ON(sizeof(struct westwood) > TCP_CA_PRIV_SIZE);
+	return tcp_register_congestion_control(&tcp_westwood);
+}
+
+static void __exit tcp_westwood_unregister(void)
+{
+	tcp_unregister_congestion_control(&tcp_westwood);
+}
+
+module_init(tcp_westwood_register);
+module_exit(tcp_westwood_unregister);
+
+MODULE_AUTHOR("Stephen Hemminger, Angelo Dell'Aera");
+MODULE_LICENSE("GPL");
+MODULE_DESCRIPTION("TCP Westwood+");