If the incomplete listen queue for a given socket is full,

drop the oldest entry in the queue.

There was a fair bit of discussion as to whether or not the
proper action is to drop a random entry in the queue.  It's
my conclusion that a random drop is better than a head drop,
however profiling this section of code (done by John Capo)
shows that a head-drop results in a significant performance
increase.

There are scenarios where a random drop is more appropriate.
If I find one in reality, I'll add the random drop code under
a conditional.

Obtained from: discussions and code done by Vernon Schryver (vjs@sgi.com).

1 files changed, 18 insertions, 5 deletions

diff --git a/sys/netinet/tcp_reass.c b/sys/netinet/tcp_reass.c
index 75a33e6..d861efe 100644
--- a/sys/netinet/tcp_reass.c
+++ b/sys/netinet/tcp_reass.c
@@ -31,7 +31,7 @@
  * SUCH DAMAGE.
  *
  *	@(#)tcp_input.c	8.12 (Berkeley) 5/24/95
- *	$Id: tcp_input.c,v 1.47 1996/09/13 18:47:03 pst Exp $
+ *	$Id: tcp_input.c,v 1.48 1996/09/13 23:51:41 pst Exp $
  */
 
 #ifndef TUBA_INCLUDE
@@ -410,11 +410,24 @@ findpcb:
 #endif
 		if (so->so_options & SO_ACCEPTCONN) {
 			register struct tcpcb *tp0 = tp;
-			so = sonewconn(so, 0);
-			if (so == 0) {
-				tcpstat.tcps_listendrop++;
-				goto drop;
+			struct socket *so2;
+			/*
+			 * If the attempt to get onto the socket queue failed,
+			 * drop the oldest queue entry and try again.
+			 */
+			so2 = sonewconn(so, 0);
+			if (!so2) {
+				so2 = TAILQ_FIRST(&so->so_incom);
+				if (so2) {
+					tcp_drop(sototcpcb(so2), ETIMEDOUT);
+					so2 = sonewconn(so, 0);
+				}
+				if (!so2) {
+					tcpstat.tcps_listendrop++;
+					goto drop;
+				}
 			}
+			so = so2;
 			/*
 			 * This is ugly, but ....
 			 *