Scalable TCP

This patch implements Tom Kelly's Scalable TCP congestion control algorithm for the modular framework.

The algorithm has some nice scaling properties, and has been used a fair bit in research, though is known to have significant fairness issues, so it's not really suitable for general purpose use.

Index: net/ipv4/Kconfig
===================================================================
@@ -481,6 +481,15 @@

        window. TCP Vegas should provide less packet loss, but it is not as aggressive as TCP Reno.

+config TCP_CONG_SCALABLE
+       tristate "Scalable TCP"
+       depends on EXPERIMENTAL
+       default n
+       ---help---
+       Scalable TCP is a sender-side only change to TCP which uses a +       MIMD congestion control algorithm which has some nice scaling +       properties, though is known to have fairness issues. +       See http://www-lce.eng.cam.ac.uk/~ctk21/scalable/

 endmenu

Index: net/ipv4/Makefile
===================================================================
@@ -35,6 +35,7 @@

 obj-$(CONFIG_TCP_CONG_HYBLA) += tcp_hybla.o obj-$(CONFIG_TCP_CONG_HTCP) += tcp_htcp.o obj-$(CONFIG_TCP_CONG_VEGAS) += tcp_vegas.o +obj-$(CONFIG_TCP_CONG_SCALABLE) += tcp_scalable.o

 obj-$(CONFIG_XFRM) += xfrm4_policy.o xfrm4_state.o xfrm4_input.o \
                      xfrm4_output.o

Index: net/ipv4/tcp_scalable.c
===================================================================

4130df8533b79d0ccfd0195e707f4aa60a527e41/net/ipv4/tcp_scalable.c  (mode:100644) @@ -0,0 +1,71 @@
+/* Tom Kelly's Scalable TCP
+ *
+ * See http://www-lce.eng.cam.ac.uk/~ctk21/scalable/
+ *
+ * John Heffner <[email protected]>
+ */
+
+#include <linux/config.h>
+#include <linux/module.h>
+#include <net/tcp.h>
+
+/* These factors derived from the recommended values in the paper:
+ * .01 and and 7/8.  We use 50 instead of 100 to account for
+ * delayed ack. */
+#define TCP_SCALABLE_AI_CNT    50U
+#define TCP_SCALABLE_MD_SCALE  3
+
+static void tcp_scalable_cong_avoid(struct tcp_sock *tp, u32 ack, u32 rtt,
+                                   u32 in_flight, int flag)
+{
+       if (in_flight < tp->snd_cwnd)
+               return;
+
+       if (tp->snd_cwnd <= tp->snd_ssthresh) {
+               tp->snd_cwnd++;
+       } else {
+               tp->snd_cwnd_cnt++;
+               if (tp->snd_cwnd_cnt > min(tp->snd_cwnd, TCP_SCALABLE_AI_CNT)) {
+                       tp->snd_cwnd++;
+                       tp->snd_cwnd_cnt = 0;
+               }
+       }
+       tp->snd_cwnd = min(tp->snd_cwnd, (__u32)tp->snd_cwnd_clamp); +       tp->snd_cwnd_stamp = tcp_time_stamp;
+}
+
+static u32 tcp_scalable_ssthresh(struct tcp_sock *tp)
+{
+       return max(tp->snd_cwnd - (tp->snd_cwnd>>TCP_SCALABLE_MD_SCALE), 2U); +}
+
+static u32 tcp_scalable_min_cwnd(struct tcp_sock *tp)
+{
+       return tp->snd_ssthresh / 2;
+}
+
+static struct tcp_congestion_ops tcp_scalable = {
+       .ssthresh       = tcp_scalable_ssthresh,
+       .cong_avoid     = tcp_scalable_cong_avoid,
+       .min_cwnd       = tcp_scalable_min_cwnd,
+
+       .owner          = THIS_MODULE,
+       .name           = "scalable"
+};
+
+static int __init tcp_scalable_register(void)
+{
+       return tcp_register_congestion_control(&tcp_scalable);
+}
+
+static void __exit tcp_scalable_unregister(void)
+{
+       tcp_unregister_congestion_control(&tcp_scalable);
+}
+
+module_init(tcp_scalable_register); +module_exit(tcp_scalable_unregister);
+
+MODULE_AUTHOR("John Heffner");
+MODULE_LICENSE("GPL");
+MODULE_DESCRIPTION("Scalable TCP");

Okay, integrated it but there were some funky whitespace issues probably because of mailer stuff.

Here is a whitespace cleaned up version of John's scaleable TCP patch to go with the other TCP congestion algorithms, to put in -mm.
--------
This patch implements Tom Kelly's Scalable TCP congestion control algorithm for the modular framework.

The algorithm has some nice scaling properties, and has been used a fair bit in research, though is known to have significant fairness issues, so it's not really suitable for general purpose use.

Index: 2.6.12-rc5-tcp3/net/ipv4/Makefile
===================================================================
@@ -35,6 +35,7 @@ obj-$(CONFIG_TCP_CONG_HSTCP) += tcp_high
 obj-$(CONFIG_TCP_CONG_HYBLA) += tcp_hybla.o
 obj-$(CONFIG_TCP_CONG_HTCP) += tcp_htcp.o
 obj-$(CONFIG_TCP_CONG_VEGAS) += tcp_vegas.o
+obj-$(CONFIG_TCP_CONG_SCALABLE) += tcp_scalable.o
 
 obj-$(CONFIG_XFRM) += xfrm4_policy.o xfrm4_state.o xfrm4_input.o \
 		      xfrm4_output.o

Index: 2.6.12-rc5-tcp3/net/ipv4/Kconfig
===================================================================
@@ -481,6 +481,15 @@ config TCP_CONG_VEGAS
 	window. TCP Vegas should provide less packet loss, but it is
 	not as aggressive as TCP Reno.
 
+config TCP_CONG_SCALABLE
+	tristate "Scalable TCP"
+	depends on EXPERIMENTAL
+	default n
+	---help---
+	Scalable TCP is a sender-side only change to TCP which uses a
+	MIMD congestion control algorithm which has some nice scaling
+	properties, though is known to have fairness issues.
+	See http://www-lce.eng.cam.ac.uk/~ctk21/scalable/
 
 endmenu