Make the initial congestion window configurable via sysctl.

MFC after: 2 weeks.

3 files changed, 29 insertions, 7 deletions

diff --git a/sys/netinet/sctp_cc_functions.c b/sys/netinet/sctp_cc_functions.c
index 8d2afc6..e40639b 100644
--- a/sys/netinet/sctp_cc_functions.c
+++ b/sys/netinet/sctp_cc_functions.c
@@ -44,18 +44,27 @@
 #include <netinet/sctp_cc_functions.h>
 #include <sys/cdefs.h>
 __FBSDID("$FreeBSD$");
+
 void
 sctp_set_initial_cc_param(struct sctp_tcb *stcb, struct sctp_nets *net)
 {
+	struct sctp_association *assoc;
+	uint32_t cwnd_in_mtu;
+
+	assoc = &stcb->asoc;
 	/*
-	 * We take the max of the burst limit times a MTU or the
-	 * INITIAL_CWND. We then limit this to 4 MTU's of sending. cwnd must
-	 * be at least 2 MTU.
+	 * We take the minimum of the burst limit and the initial congestion
+	 * window. The initial congestion window is at least two times the
+	 * MTU.
 	 */
-	net->cwnd = min((net->mtu * 4), max((2 * net->mtu), SCTP_INITIAL_CWND));
-	net->ssthresh = stcb->asoc.peers_rwnd;
-
-	if (SCTP_BASE_SYSCTL(sctp_logging_level) & (SCTP_CWND_MONITOR_ENABLE | SCTP_CWND_LOGGING_ENABLE)) {
+	cwnd_in_mtu = SCTP_BASE_SYSCTL(sctp_initial_cwnd);
+	if ((assoc->max_burst > 0) && (cwnd_in_mtu > assoc->max_burst))
+		cwnd_in_mtu = assoc->max_burst;
+	net->cwnd = (net->mtu - sizeof(struct sctphdr)) * cwnd_in_mtu;
+	net->ssthresh = assoc->peers_rwnd;
+
+	if (SCTP_BASE_SYSCTL(sctp_logging_level) &
+	    (SCTP_CWND_MONITOR_ENABLE | SCTP_CWND_LOGGING_ENABLE)) {
 		sctp_log_cwnd(stcb, net, 0, SCTP_CWND_INITIALIZATION);
 	}
 }
diff --git a/sys/netinet/sctp_sysctl.c b/sys/netinet/sctp_sysctl.c
index ef1356c..9e0c56e 100644
--- a/sys/netinet/sctp_sysctl.c
+++ b/sys/netinet/sctp_sysctl.c
@@ -110,6 +110,7 @@ sctp_init_sysctls()
 	SCTP_BASE_SYSCTL(sctp_mobility_fasthandoff) = SCTPCTL_MOBILITY_FASTHANDOFF_DEFAULT;
 	SCTP_BASE_SYSCTL(sctp_vtag_time_wait) = SCTPCTL_TIME_WAIT_DEFAULT;
 	SCTP_BASE_SYSCTL(sctp_buffer_splitting) = SCTPCTL_BUFFER_SPLITTING_DEFAULT;
+	SCTP_BASE_SYSCTL(sctp_initial_cwnd) = SCTPCTL_INITIAL_CWND_DEFAULT;
 #if defined(SCTP_LOCAL_TRACE_BUF)
 	memset(&SCTP_BASE_SYSCTL(sctp_log), 0, sizeof(struct sctp_log));
 #endif
@@ -622,6 +623,7 @@ sysctl_sctp_check(SYSCTL_HANDLER_ARGS)
 		RANGECHK(SCTP_BASE_SYSCTL(sctp_default_frag_interleave), SCTPCTL_DEFAULT_FRAG_INTERLEAVE_MIN, SCTPCTL_DEFAULT_FRAG_INTERLEAVE_MAX);
 		RANGECHK(SCTP_BASE_SYSCTL(sctp_vtag_time_wait), SCTPCTL_TIME_WAIT_MIN, SCTPCTL_TIME_WAIT_MAX);
 		RANGECHK(SCTP_BASE_SYSCTL(sctp_buffer_splitting), SCTPCTL_BUFFER_SPLITTING_MIN, SCTPCTL_BUFFER_SPLITTING_MAX);
+		RANGECHK(SCTP_BASE_SYSCTL(sctp_initial_cwnd), SCTPCTL_INITIAL_CWND_MIN, SCTPCTL_INITIAL_CWND_MAX);
 		RANGECHK(SCTP_BASE_SYSCTL(sctp_mobility_base), SCTPCTL_MOBILITY_BASE_MIN, SCTPCTL_MOBILITY_BASE_MAX);
 		RANGECHK(SCTP_BASE_SYSCTL(sctp_mobility_fasthandoff), SCTPCTL_MOBILITY_FASTHANDOFF_MIN, SCTPCTL_MOBILITY_FASTHANDOFF_MAX);
 		RANGECHK(SCTP_BASE_SYSCTL(sctp_udp_tunneling_for_client_enable), SCTPCTL_UDP_TUNNELING_FOR_CLIENT_ENABLE_MIN, SCTPCTL_UDP_TUNNELING_FOR_CLIENT_ENABLE_MAX);
@@ -1072,6 +1074,10 @@ SYSCTL_PROC(_net_inet_sctp, OID_AUTO, buffer_splitting, CTLTYPE_INT | CTLFLAG_RW
     &SCTP_BASE_SYSCTL(sctp_buffer_splitting), 0, sysctl_sctp_check, "IU",
     SCTPCTL_BUFFER_SPLITTING_DESC);
 
+SYSCTL_PROC(_net_inet_sctp, OID_AUTO, initial_cwnd, CTLTYPE_INT | CTLFLAG_RW,
+    &SCTP_BASE_SYSCTL(sctp_initial_cwnd), 0, sysctl_sctp_check, "IU",
+    SCTPCTL_INITIAL_CWND_DESC);
+
 #ifdef SCTP_DEBUG
 SYSCTL_PROC(_net_inet_sctp, OID_AUTO, debug, CTLTYPE_INT | CTLFLAG_RW,
     &SCTP_BASE_SYSCTL(sctp_debug_on), 0, sysctl_sctp_check, "IU",
diff --git a/sys/netinet/sctp_sysctl.h b/sys/netinet/sctp_sysctl.h
index e52f40d..99ecd03 100644
--- a/sys/netinet/sctp_sysctl.h
+++ b/sys/netinet/sctp_sysctl.h
@@ -108,6 +108,7 @@ struct sctp_sysctl {
 	uint32_t sctp_enable_sack_immediately;
 	uint32_t sctp_vtag_time_wait;
 	uint32_t sctp_buffer_splitting;
+	uint32_t sctp_initial_cwnd;
 #if defined(SCTP_DEBUG)
 	uint32_t sctp_debug_on;
 #endif
@@ -497,6 +498,12 @@ struct sctp_sysctl {
 #define SCTPCTL_BUFFER_SPLITTING_MAX		0x3
 #define SCTPCTL_BUFFER_SPLITTING_DEFAULT	SCTPCTL_BUFFER_SPLITTING_MIN
 
+/* Initial congestion window in MTU */
+#define SCTPCTL_INITIAL_CWND_DESC	"Initial congestion window in MTU"
+#define SCTPCTL_INITIAL_CWND_MIN	2
+#define SCTPCTL_INITIAL_CWND_MAX	0xffffffff
+#define SCTPCTL_INITIAL_CWND_DEFAULT	3
+
 #if defined(SCTP_DEBUG)
 /* debug: Configure debug output */
 #define SCTPCTL_DEBUG_DESC	"Configure debug output"