svn commit: r249809 - head/sys/netinet

Andre Oppermann andre at FreeBSD.org
Tue Apr 23 14:06:33 UTC 2013


Author: andre
Date: Tue Apr 23 14:06:32 2013
New Revision: 249809
URL: http://svnweb.freebsd.org/changeset/base/249809

Log:
  When doing RFC3042 limited transmit on the first on second
  duplicate ACK make sure we actually have new data to send.
  This prevents us from sending unneccessary pure ACKs.
  
  Reported by:	Matt Miller <matt at matthewjmiller.net>
  Tested by:	Matt Miller <matt at matthewjmiller.net>
  MFC after:	2 weeks

Modified:
  head/sys/netinet/tcp_input.c

Modified: head/sys/netinet/tcp_input.c
==============================================================================
--- head/sys/netinet/tcp_input.c	Tue Apr 23 13:33:13 2013	(r249808)
+++ head/sys/netinet/tcp_input.c	Tue Apr 23 14:06:32 2013	(r249809)
@@ -2564,6 +2564,7 @@ tcp_do_segment(struct mbuf *m, struct tc
 					u_long oldcwnd = tp->snd_cwnd;
 					tcp_seq oldsndmax = tp->snd_max;
 					u_int sent;
+					int avail;
 
 					KASSERT(tp->t_dupacks == 1 ||
 					    tp->t_dupacks == 2,
@@ -2585,7 +2586,17 @@ tcp_do_segment(struct mbuf *m, struct tc
 						 */
 						break;
 					}
-					(void) tcp_output(tp);
+					/*
+					 * Only call tcp_output when there
+					 * is new data available to be sent.
+					 * Otherwise we would send pure ACKs.
+					 */
+					SOCKBUF_LOCK(&so->so_snd);
+					avail = so->so_snd.sb_cc -
+					    (tp->snd_nxt - tp->snd_una);
+					SOCKBUF_UNLOCK(&so->so_snd);
+					if (avail > 0)
+						(void) tcp_output(tp);
 					sent = tp->snd_max - oldsndmax;
 					if (sent > tp->t_maxseg) {
 						KASSERT((tp->t_dupacks == 2 &&


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