Module Name: src
Committed By: christos
Date: Mon Apr 27 16:50:17 UTC 2015
Modified Files:
src/sys/netinet: tcp_output.c
Log Message:
Apply Revision 220794 from FreeBSD to avoid dup ACKs:
When checking to see if a window update should be sent to the remote peer,
don't force a window update if the window would not actually grow due to
window scaling. Specifically, if the window scaling factor is larger than
2 * MSS, then after the local reader has drained 2 * MSS bytes from the
socket, a window update can end up advertising the same window. If this
happens, the supposed window update actually ends up being a duplicate ACK.
This can result in an excessive number of duplicate ACKs when using a
higher maximum socket buffer size.
Pointed out by Ricky Charlet, in tech-net.
To generate a diff of this commit:
cvs rdiff -u -r1.181 -r1.182 src/sys/netinet/tcp_output.c
Please note that diffs are not public domain; they are subject to the
copyright notices on the relevant files.
Modified files:
Index: src/sys/netinet/tcp_output.c
diff -u src/sys/netinet/tcp_output.c:1.181 src/sys/netinet/tcp_output.c:1.182
--- src/sys/netinet/tcp_output.c:1.181 Sun Apr 26 22:59:44 2015
+++ src/sys/netinet/tcp_output.c Mon Apr 27 12:50:17 2015
@@ -1,4 +1,4 @@
-/* $NetBSD: tcp_output.c,v 1.181 2015/04/27 02:59:44 ozaki-r Exp $ */
+/* $NetBSD: tcp_output.c,v 1.182 2015/04/27 16:50:17 christos Exp $ */
/*
* Copyright (C) 1995, 1996, 1997, and 1998 WIDE Project.
@@ -135,7 +135,7 @@
*/
#include <sys/cdefs.h>
-__KERNEL_RCSID(0, "$NetBSD: tcp_output.c,v 1.181 2015/04/27 02:59:44 ozaki-r Exp $");
+__KERNEL_RCSID(0, "$NetBSD: tcp_output.c,v 1.182 2015/04/27 16:50:17 christos Exp $");
#include "opt_inet.h"
#include "opt_ipsec.h"
@@ -1020,11 +1020,19 @@ again:
long adv = min(win, (long)TCP_MAXWIN << tp->rcv_scale) -
(tp->rcv_adv - tp->rcv_nxt);
+ /*
+ * If the new window size ends up being the same as the old
+ * size when it is scaled, then don't force a window update.
+ */
+ if ((tp->rcv_adv - tp->rcv_nxt) >> tp->rcv_scale ==
+ (adv + tp->rcv_adv - tp->rcv_nxt) >> tp->rcv_scale)
+ goto dontupdate;
if (adv >= (long) (2 * rxsegsize))
goto send;
if (2 * adv >= (long) so->so_rcv.sb_hiwat)
goto send;
}
+dontupdate:
/*
* Send if we owe peer an ACK.
