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[PATCH 3/5] TCP Westwood+ support

To: Andrew Morton <akpm@xxxxxxxxx>, "David S. Miller" <davem@xxxxxxxxxxxxx>
Subject: [PATCH 3/5] TCP Westwood+ support
From: Stephen Hemminger <shemminger@xxxxxxxx>
Date: Fri, 18 Mar 2005 16:24:12 -0800
Cc: netdev@xxxxxxxxxxx
Organization: Open Source Development Lab
Sender: netdev-bounce@xxxxxxxxxxx
Add TCP Westwood+ support back in as a separate pluggable algorithm.
The mechanism and policy is unchanged from existing code.

Signed-off-by: Stephen Hemminger <shemminger@xxxxxxxx>


diff -Nru a/net/ipv4/Kconfig b/net/ipv4/Kconfig
--- a/net/ipv4/Kconfig  2005-03-18 16:10:43 -08:00
+++ b/net/ipv4/Kconfig  2005-03-18 16:10:43 -08:00
@@ -382,6 +382,20 @@
        increase provides TCP friendliness.
        See http://www.csc.ncsu.edu/faculty/rhee/export/bitcp/
 
+config TCP_CONG_WESTWOOD
+       tristate "TCP Westwood+"
+       default y
+       ---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 -Nru a/net/ipv4/Makefile b/net/ipv4/Makefile
--- a/net/ipv4/Makefile 2005-03-18 16:10:43 -08:00
+++ b/net/ipv4/Makefile 2005-03-18 16:10:43 -08:00
@@ -25,6 +25,7 @@
 obj-$(CONFIG_IP_VS) += ipvs/
 obj-$(CONFIG_IP_TCPDIAG) += tcp_diag.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 -Nru a/net/ipv4/tcp_westwood.c b/net/ipv4/tcp_westwood.c
--- /dev/null   Wed Dec 31 16:00:00 196900
+++ b/net/ipv4/tcp_westwood.c   2005-03-18 16:10:43 -08:00
@@ -0,0 +1,349 @@
+/*
+ * 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_ca {
+       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_INIT_RTT  (20*HZ)           /* maybe too conservative?! */
+#define TCP_WESTWOOD_RTT_MIN   (HZ/20)           /* 50ms */
+
+/*
+ * @tcp_westwood_create
+ * This function initializes fields used in TCP Westwood+. We can't
+ * get 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_start(struct tcp_sock *tp)
+{
+       struct westwood_ca *w = tcp_ca(tp);
+
+        w->bw_ns_est = 0;
+        w->bw_est = 0;
+        w->accounted = 0;
+        w->cumul_ack = 0;
+        w->rtt_win_sx = tcp_time_stamp;
+        w->rtt = TCP_WESTWOOD_INIT_RTT;
+        w->rtt_min = TCP_WESTWOOD_INIT_RTT;
+        w->snd_una = tp->snd_una;
+}
+
+/*
+ * @westwood_do_filter
+ * Low-pass filter. Implemented using constant coefficents.
+ */
+static inline u32 westwood_do_filter(u32 a, u32 b)
+{
+       return (((7 * a) + b) >> 3);
+}
+
+static inline void westwood_filter(struct westwood_ca *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_update_rttmin
+ * It is used to update RTTmin. In this case we MUST NOT use
+ * WESTWOOD_RTT_MIN minimum bound since we could be on a LAN!
+ */
+static inline u32 westwood_update_rttmin(const struct westwood_ca *w)
+{
+       u32 rttmin = w->rtt_min;
+
+       if (w->rtt != 0 &&
+           (w->rtt < w->rtt_min || !rttmin))
+               rttmin = w->rtt;
+
+       return rttmin;
+}
+
+static void tcp_westwood_sample_rtt(struct tcp_sock *tp, u32 rtt)
+{
+       struct westwood_ca *w = tcp_ca(tp);
+       w->rtt = tp->srtt >> 3;
+}
+
+/*
+ * @westwood_acked
+ * Evaluate increases for dk.
+ */
+static inline u32 westwood_acked(struct tcp_sock *tp)
+{
+       struct westwood_ca *w = tcp_ca(tp);
+       return tp->snd_una - w->snd_una;
+}
+
+/*
+ * @westwood_new_window
+ * It evaluates if we are receiving data inside the same RTT window as
+ * when we started.
+ * Return value:
+ * It returns 0 if we are still evaluating samples in the same RTT
+ * window, 1 if the sample has to be considered in the next window.
+ */
+static inline int westwood_new_window(const struct tcp_sock *tp)
+{
+       struct westwood_ca *w = tcp_ca(tp);
+       u32 left_bound;
+       u32 rtt;
+       int ret = 0;
+
+       left_bound = w->rtt_win_sx;
+       rtt = max(w->rtt, (u32) TCP_WESTWOOD_RTT_MIN);
+
+       /*
+        * 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 choosen since an estimation on small
+        * time intervals is better to avoid...
+        * Obvioulsy on a LAN we reasonably will always have
+        * right_bound = left_bound + WESTWOOD_RTT_MIN
+         */
+
+       if ((left_bound + rtt) < tcp_time_stamp)
+               ret = 1;
+
+       return ret;
+}
+
+/*
+ * @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, u32 now)
+{
+       struct westwood_ca *w = tcp_ca(tp);
+       if (westwood_new_window(tp)) {
+               u32 delta = now - w->rtt_win_sx;
+
+               if (delta) {
+                       if (w->rtt)
+                               westwood_filter(w, delta);
+
+                       w->bk = 0;
+                       w->rtt_win_sx = tcp_time_stamp;
+               }
+       }
+}
+
+/*
+ * @tcp_westwood_fast_bw
+ * It is called when we are in fast path. In particular it is called when
+ * header prediction is successfull. In such case infact update is
+ * straight forward and doesn't need any particular care.
+ */
+static void tcp_westwood_fast_bw(struct tcp_sock *tp)
+{
+       struct westwood_ca *w = tcp_ca(tp);
+       westwood_update_window(tp, tcp_time_stamp);
+
+       w->bk += westwood_acked(tp);
+       w->snd_una = tp->snd_una;
+       w->rtt_min = westwood_update_rttmin(w);
+}
+
+/*
+ * @westwood_acked_count
+ * This function evaluates cumul_ack for evaluating dk in case of
+ * delayed or partial acks.
+ */
+static u32 westwood_acked_count(struct tcp_sock *tp)
+{
+       struct westwood_ca *w = tcp_ca(tp);
+
+       w->cumul_ack = westwood_acked(tp);
+
+        /* 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_std;
+               w->cumul_ack = tp->mss_cache_std;
+       }
+
+        if (w->cumul_ack > tp->mss_cache_std) {
+               /* Partial or delayed ack */
+               if (w->accounted >= w->cumul_ack) {
+                       w->accounted -= w->cumul_ack;
+                       w->cumul_ack = tp->mss_cache_std;
+               } else {
+                       w->cumul_ack -= w->accounted;
+                       w->accounted = 0;
+               }
+       }
+
+       w->snd_una = tp->snd_una;
+
+       return w->cumul_ack;
+}
+
+
+/*
+ * @tcp_westwood_slow_bw
+ * It is called when something is going wrong..even if there could
+ * be no problems! Infact a simple delayed packet may trigger a
+ * dupack. But we need to be careful in such case.
+ */
+static void tcp_westwood_slow_bw(struct tcp_sock *tp)
+{
+       struct westwood_ca *w = tcp_ca(tp);
+
+       westwood_update_window(tp, tcp_time_stamp);
+
+       w->bk += westwood_acked_count(tp);
+       w->rtt_min = westwood_update_rttmin(w);
+}
+
+static inline u32 tcp_westwood_bw_rttmin(const struct tcp_sock *tp)
+{
+       struct westwood_ca *w = tcp_ca(tp);
+
+        return max((w->bw_est) * (w->rtt_min) / (u32) (tp->mss_cache_std),
+                  2U);
+}
+
+static inline u32 tcp_westwood_ssthresh(struct tcp_sock *tp)
+{
+       u32 ssthresh = tcp_westwood_bw_rttmin(tp);
+       if (ssthresh)
+               tp->snd_ssthresh = ssthresh;
+
+       return (ssthresh != 0);
+}
+
+static inline int tcp_westwood_cwnd(struct tcp_sock *tp)
+{
+       u32 cwnd = 0;
+
+       cwnd = tcp_westwood_bw_rttmin(tp);
+       if (cwnd)
+               tp->snd_cwnd = cwnd;
+
+       return (cwnd != 0);
+}
+
+/*
+ * TCP Westwood
+ * Here limit is evaluated as BWestimation*RTTmin (for obtaining it
+ * in packets we use mss_cache). If sysctl_tcp_westwood is off
+ * tcp_westwood_bw_rttmin() returns 0. In such case snd_ssthresh is
+ * still used as usual. It prevents other strange cases in which
+ * BWE*RTTmin could assume value 0. It should not happen but...
+ */
+static u32 tcp_westwood_cwnd_min(struct tcp_sock *tp)
+{
+       u32 limit;
+
+       limit = tcp_westwood_bw_rttmin(tp);
+       if (limit == 0)
+               limit = tp->snd_ssthresh/2;
+       return limit;
+}
+
+static void tcp_westwood_event(struct tcp_sock *tp, enum tcp_ca_event event)
+{
+       switch(event) {
+       case CA_EVENT_CWND_RESTART:
+               break;
+
+       case CA_EVENT_COMPLETE_CWR:
+               if (tcp_westwood_cwnd(tp))
+                       tp->snd_ssthresh = tp->snd_cwnd;
+               break;
+
+       case CA_EVENT_FRTO:
+               if (!tcp_westwood_ssthresh(tp))
+                       tp->snd_ssthresh = tcp_westwood_ssthresh(tp);
+               break;
+
+       case CA_EVENT_FAST_ACK:
+               tcp_westwood_fast_bw(tp);
+               break;
+
+       case CA_EVENT_SLOW_ACK:
+               tcp_westwood_slow_bw(tp);
+               break;
+
+       default:
+               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)
+{
+
+       if (ext & (1<<(TCPDIAG_VEGASINFO-1))) {
+               struct tcpvegas_info *info
+                       = tcpdiag_put(skb, TCPDIAG_VEGASINFO, sizeof(*info));
+               if (info) {
+                       struct westwood_ca *ca = tcp_ca(tp);
+                       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);
+               }
+       }
+}
+
+
+static struct tcp_ca_type tcp_westwood = {
+       .start          = tcp_westwood_start,
+       .ssthresh       = tcp_reno_ssthresh,
+       .rtt_sample     = tcp_westwood_sample_rtt,
+       .cong_avoid     = tcp_reno_cong_avoid,
+       .min_cwnd       = tcp_westwood_cwnd_min,
+       .cwnd_event     = tcp_westwood_event,
+       .get_info       = tcp_westwood_info,
+
+       .owner          = THIS_MODULE,
+       .name           = "westwood"
+};
+
+static int __init tcp_westwood_init(void)
+{
+       BUG_ON(sizeof(struct westwood_ca) > TCP_CA_PRIV_SIZE);
+       tcp_ca_register(&tcp_westwood);
+       return 0;
+}
+
+static void __exit tcp_westwood_exit(void)
+{
+       tcp_ca_unregister(&tcp_westwood);
+}
+
+module_init(tcp_westwood_init);
+module_exit(tcp_westwood_exit);
+
+MODULE_AUTHOR("Stephen Hemminger, Angelo Del'Aera");
+MODULE_LICENSE("GPL");
+MODULE_DESCRIPTION("TCP Westwood+");

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