[TCP]: Add Scalable TCP congestion control module.

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. Signed-off-by: John Heffner <jheffner@psc.edu> Signed-off-by: David S. Miller <davem@davemloft.net>

[TCP]: Add Scalable TCP congestion control module.
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. Signed-off-by: John Heffner <jheffner@psc.edu> Signed-off-by: David S. Miller <davem@davemloft.net>
John Heffner · David S. Miller
1 parent a7868ea68d
Showing 3 changed files with 78 additions and 0 deletions Side-by-side Diff
net/ipv4/Kconfig
net/ipv4/Makefile
net/ipv4/tcp_scalable.c
@@ -511,6 +511,15 @@
 	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 INET && 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
  
@@ -37,6 +37,7 @@
 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
+/* Tom Kelly's Scalable TCP
+ *
+ * See htt://www-lce.eng.cam.ac.uk/~ctk21/scalable/
+ *
+ * John Heffner <jheffner@sc.edu>
+ */
+
+#include <linux/config.h>
+#include <linux/module.h>
+#include <net/tcp.h>
+
+/* These factors derived from the recommended values in the aer:
+ * .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_t(u32, tp->snd_cwnd, 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 struct tcp_congestion_ops tcp_scalable = {
+	.ssthresh	= tcp_scalable_ssthresh,
+	.cong_avoid	= tcp_scalable_cong_avoid,
+	.min_cwnd	= tcp_reno_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");
...	...	@@ -511,6 +511,15 @@
511	511	window. TCP Vegas should provide less packet loss, but it is
512	512	not as aggressive as TCP Reno.
513	513
	514	+config TCP_CONG_SCALABLE
	515	+ tristate "Scalable TCP"
	516	+ depends on INET && EXPERIMENTAL
	517	+ default n
	518	+ ---help---
	519	+ Scalable TCP is a sender-side only change to TCP which uses a
	520	+ MIMD congestion control algorithm which has some nice scaling
	521	+ properties, though is known to have fairness issues.
	522	+ See http://www-lce.eng.cam.ac.uk/~ctk21/scalable/
514	523
515	524	endmenu
516	525
...	...	@@ -37,6 +37,7 @@
37	37	obj-$(CONFIG_TCP_CONG_HYBLA) += tcp_hybla.o
38	38	obj-$(CONFIG_TCP_CONG_HTCP) += tcp_htcp.o
39	39	obj-$(CONFIG_TCP_CONG_VEGAS) += tcp_vegas.o
	40	+obj-$(CONFIG_TCP_CONG_SCALABLE) += tcp_scalable.o
40	41
41	42	obj-$(CONFIG_XFRM) += xfrm4_policy.o xfrm4_state.o xfrm4_input.o \
42	43	xfrm4_output.o
	1	+/* Tom Kelly's Scalable TCP
	2	+ *
	3	+ * See htt://www-lce.eng.cam.ac.uk/~ctk21/scalable/
	4	+ *
	5	+ * John Heffner <jheffner@sc.edu>
	6	+ */
	7	+
	8	+#include <linux/config.h>
	9	+#include <linux/module.h>
	10	+#include <net/tcp.h>
	11	+
	12	+/* These factors derived from the recommended values in the aer:
	13	+ * .01 and and 7/8. We use 50 instead of 100 to account for
	14	+ * delayed ack.
	15	+ */
	16	+#define TCP_SCALABLE_AI_CNT 50U
	17	+#define TCP_SCALABLE_MD_SCALE 3
	18	+
	19	+static void tcp_scalable_cong_avoid(struct tcp_sock *tp, u32 ack, u32 rtt,
	20	+ u32 in_flight, int flag)
	21	+{
	22	+ if (in_flight < tp->snd_cwnd)
	23	+ return;
	24	+
	25	+ if (tp->snd_cwnd <= tp->snd_ssthresh) {
	26	+ tp->snd_cwnd++;
	27	+ } else {
	28	+ tp->snd_cwnd_cnt++;
	29	+ if (tp->snd_cwnd_cnt > min(tp->snd_cwnd, TCP_SCALABLE_AI_CNT)){
	30	+ tp->snd_cwnd++;
	31	+ tp->snd_cwnd_cnt = 0;
	32	+ }
	33	+ }
	34	+ tp->snd_cwnd = min_t(u32, tp->snd_cwnd, tp->snd_cwnd_clamp);
	35	+ tp->snd_cwnd_stamp = tcp_time_stamp;
	36	+}
	37	+
	38	+static u32 tcp_scalable_ssthresh(struct tcp_sock *tp)
	39	+{
	40	+ return max(tp->snd_cwnd - (tp->snd_cwnd>>TCP_SCALABLE_MD_SCALE), 2U);
	41	+}
	42	+
	43	+
	44	+static struct tcp_congestion_ops tcp_scalable = {
	45	+ .ssthresh = tcp_scalable_ssthresh,
	46	+ .cong_avoid = tcp_scalable_cong_avoid,
	47	+ .min_cwnd = tcp_reno_min_cwnd,
	48	+
	49	+ .owner = THIS_MODULE,
	50	+ .name = "scalable",
	51	+};
	52	+
	53	+static int __init tcp_scalable_register(void)
	54	+{
	55	+ return tcp_register_congestion_control(&tcp_scalable);
	56	+}
	57	+
	58	+static void __exit tcp_scalable_unregister(void)
	59	+{
	60	+ tcp_unregister_congestion_control(&tcp_scalable);
	61	+}
	62	+
	63	+module_init(tcp_scalable_register);
	64	+module_exit(tcp_scalable_unregister);
	65	+
	66	+MODULE_AUTHOR("John Heffner");
	67	+MODULE_LICENSE("GPL");
	68	+MODULE_DESCRIPTION("Scalable TCP");