[TCP]: Port 2.4.x version of TCP Westwood support to 2.6.x

Original 2.4.x version by Angelo Dell'Aera (buffer@antifork.org)

Here is the 2.4 version with some cleanups converted to 2.6.
- use tcp_ prefix (dave)
- get rid of rwlock not needed (dave)
- do some hand optimization of the inline's
- don't make init inline
- get rid of extra whitespace
- eliminate accessor for mss_cache

include/linux/sysctl.h

@@ -311,6 +311,7 @@ enum
 	NET_TCP_FRTO=92,
 	NET_TCP_LOW_LATENCY=93,
 	NET_IPV4_IPFRAG_SECRET_INTERVAL=94,
+	NET_TCP_WESTWOOD=95,
 };
 
 enum {

include/linux/tcp.h

@@ -374,6 +374,20 @@ struct tcp_opt {
 	__u32                   frto_highmark; /* snd_nxt when RTO occurred */
 
 	unsigned long last_synq_overflow; 
+
+/* TCP Westwood structure */
+        struct {
+                __u32    bw_sample;        /* bandwidth sample */
+                __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 */
+        } westwood;
 };
 
 /* WARNING: don't change the layout of the members in tcp_sock! */

include/net/tcp.h

@@ -579,6 +579,7 @@ extern int sysctl_tcp_adv_win_scale;
 extern int sysctl_tcp_tw_reuse;
 extern int sysctl_tcp_frto;
 extern int sysctl_tcp_low_latency;
+extern int sysctl_tcp_westwood;
 
 extern atomic_t tcp_memory_allocated;
 extern atomic_t tcp_sockets_allocated;
@@ -2019,4 +2020,67 @@ struct tcp_iter_state {
 extern int tcp_proc_register(struct tcp_seq_afinfo *afinfo);
 extern void tcp_proc_unregister(struct tcp_seq_afinfo *afinfo);
 
+/* TCP Westwood functions and constants */
+
+#define TCP_WESTWOOD_INIT_RTT  (20*HZ)           /* maybe too conservative?! */
+#define TCP_WESTWOOD_RTT_MIN   (HZ/20)           /* 50ms */
+
+static inline void tcp_westwood_update_rtt(struct tcp_opt *tp, __u32 rtt_seq)
+{
+        if (sysctl_tcp_westwood)
+                tp->westwood.rtt = rtt_seq;
+}
+
+void __tcp_westwood_fast_bw(struct sock *, struct sk_buff *);
+void __tcp_westwood_slow_bw(struct sock *, struct sk_buff *);
+
+static inline void tcp_westwood_fast_bw(struct sock *sk, struct sk_buff *skb)
+{
+        if (sysctl_tcp_westwood)
+                __tcp_westwood_fast_bw(sk, skb);
+}
+
+static inline void tcp_westwood_slow_bw(struct sock *sk, struct sk_buff *skb)
+{
+        if (sysctl_tcp_westwood)
+                __tcp_westwood_slow_bw(sk, skb);
+}
+
+static inline __u32 __tcp_westwood_bw_rttmin(const struct tcp_opt *tp)
+{
+        return max((tp->westwood.bw_est) * (tp->westwood.rtt_min) /
+		   (__u32) (tp->mss_cache),
+		   2U);
+}
+
+static inline __u32 tcp_westwood_bw_rttmin(const struct tcp_opt *tp)
+{
+	return sysctl_tcp_westwood ? __tcp_westwood_bw_rttmin(tp) : 0;
+}
+
+static inline int tcp_westwood_ssthresh(struct tcp_opt *tp)
+{
+	__u32 ssthresh = 0;
+
+	if (sysctl_tcp_westwood) {
+		ssthresh = __tcp_westwood_bw_rttmin(tp);
+		if (ssthresh)
+			tp->snd_ssthresh = ssthresh;  
+	}
+
+	return (ssthresh != 0);
+}
+
+static inline int tcp_westwood_cwnd(struct tcp_opt *tp)
+{
+	__u32 cwnd = 0;
+
+	if (sysctl_tcp_westwood) {
+		cwnd = __tcp_westwood_bw_rttmin(tp);
+		if (cwnd)
+			tp->snd_cwnd = cwnd;
+	}
+
+	return (cwnd != 0);
+}
 #endif	/* _TCP_H */

net/ipv4/sysctl_net_ipv4.c

@@ -584,6 +584,14 @@ ctl_table ipv4_table[] = {
 		.proc_handler	= &proc_dointvec_jiffies,
 		.strategy	= &sysctl_jiffies
 	},
+	{
+		.ctl_name	= NET_TCP_WESTWOOD, 
+		.procname	= "tcp_westwood",
+		.data		= &sysctl_tcp_westwood,
+		.maxlen		= sizeof(int),
+		.mode		= 0644,
+		.proc_handler	= &proc_dointvec,
+	},
 	{ .ctl_name = 0 }
 };