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Apply Revision 220794 from FreeBSD to avoid dup ACKs:

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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.
This commit is contained in:
christos 2015-04-27 16:50:17 +00:00
parent 016c7d8298
commit ffe2b84e28
1 changed files with 10 additions and 2 deletions
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12
sys/netinet/tcp_output.c
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@ -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.