Author: jhb
Date: Mon Apr 18 17:43:16 2011
New Revision: 220794
URL: http://svn.freebsd.org/changeset/base/220794
Log:
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.
Reviewed by: bz
MFC after: 1 month
Modified:
head/sys/netinet/tcp_output.c
Modified: head/sys/netinet/tcp_output.c
==============================================================================
--- head/sys/netinet/tcp_output.c Mon Apr 18 16:40:47 2011
(r220793)
+++ head/sys/netinet/tcp_output.c Mon Apr 18 17:43:16 2011
(r220794)
@@ -564,11 +564,19 @@ after_sack_rexmit:
long adv = min(recwin, (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 * tp->t_maxseg))
goto send;
if (2 * adv >= (long) so->so_rcv.sb_hiwat)
goto send;
}
+dontupdate:
/*
* Send if we owe the peer an ACK, RST, SYN, or urgent data. ACKNOW
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