Date: Fri, 10 Jun 2011 18:51:33 +0000 (UTC) From: John Baldwin <jhb@FreeBSD.org> To: src-committers@freebsd.org, svn-src-all@freebsd.org, svn-src-stable@freebsd.org, svn-src-stable-7@freebsd.org Subject: svn commit: r222937 - stable/7/sys/netinet Message-ID: <201106101851.p5AIpXmx038553@svn.freebsd.org>
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Author: jhb Date: Fri Jun 10 18:51:33 2011 New Revision: 222937 URL: http://svn.freebsd.org/changeset/base/222937 Log: MFC 220794: 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. Modified: stable/7/sys/netinet/tcp_output.c Directory Properties: stable/7/sys/ (props changed) stable/7/sys/cddl/contrib/opensolaris/ (props changed) stable/7/sys/contrib/dev/acpica/ (props changed) stable/7/sys/contrib/pf/ (props changed) Modified: stable/7/sys/netinet/tcp_output.c ============================================================================== --- stable/7/sys/netinet/tcp_output.c Fri Jun 10 18:51:22 2011 (r222936) +++ stable/7/sys/netinet/tcp_output.c Fri Jun 10 18:51:33 2011 (r222937) @@ -560,11 +560,19 @@ 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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