[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>

3 files changed, 275 insertions, 0 deletions

diff --git a/net/ipv4/Kconfig b/net/ipv4/Kconfig
index 712ebacacb6..adbe855d931 100644
--- a/net/ipv4/Kconfig
+++ b/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"
diff --git a/net/ipv4/Makefile b/net/ipv4/Makefile
index 1d1cac5ac06..dedfbe62a10 100644
--- a/net/ipv4/Makefile
+++ b/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
diff --git a/net/ipv4/tcp_westwood.c b/net/ipv4/tcp_westwood.c
new file mode 100644
index 00000000000..ef827242c94
--- /dev/null
+++ b/net/ipv4/tcp_westwood.c
@@ -0,0 +1,259 @@
+/*
+ * 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+");