[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>

diff --git a/net/ipv4/Kconfig b/net/ipv4/Kconfig
index 73a25b52bf7d35589ae09de35a4d3fff42c197a3..690e88ba24846296c8c957da52ca5966bf142584 100644 (file)
--- a/net/ipv4/Kconfig
+++ b/net/ipv4/Kconfig
@@ -511,6 +511,15 @@ 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 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
 

diff --git a/net/ipv4/Makefile b/net/ipv4/Makefile
index e96ed17deb9688c4ac25bd7541a938e54b31219a..5718cdb3a61e5e5972a2f634422e14b1bd462a2d 100644 (file)
--- a/net/ipv4/Makefile
+++ b/net/ipv4/Makefile
@@ -37,6 +37,7 @@ obj-$(CONFIG_TCP_CONG_HSTCP) += tcp_highspeed.o
 obj-$(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

diff --git a/net/ipv4/tcp_scalable.c b/net/ipv4/tcp_scalable.c
new file mode 100644 (file)
index 0000000..70e108e
--- /dev/null
+++ b/net/ipv4/tcp_scalable.c
@@ -0,0 +1,68 @@
+/* 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");