Date: Mon, 18 Apr 2011 17:43:16 +0000 (UTC) From: John Baldwin <jhb@FreeBSD.org> To: src-committers@freebsd.org, svn-src-all@freebsd.org, svn-src-head@freebsd.org Subject: svn commit: r220794 - head/sys/netinet Message-ID: <201104181743.p3IHhGBf079436@svn.freebsd.org>
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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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