From owner-svn-src-head@FreeBSD.ORG Mon Apr 18 17:43:16 2011 Return-Path: Delivered-To: svn-src-head@freebsd.org Received: from mx1.freebsd.org (mx1.freebsd.org [IPv6:2001:4f8:fff6::34]) by hub.freebsd.org (Postfix) with ESMTP id E7C2B106564A; Mon, 18 Apr 2011 17:43:16 +0000 (UTC) (envelope-from jhb@FreeBSD.org) Received: from svn.freebsd.org (svn.freebsd.org [IPv6:2001:4f8:fff6::2c]) by mx1.freebsd.org (Postfix) with ESMTP id D5F488FC12; Mon, 18 Apr 2011 17:43:16 +0000 (UTC) Received: from svn.freebsd.org (localhost [127.0.0.1]) by svn.freebsd.org (8.14.3/8.14.3) with ESMTP id p3IHhGT8079438; Mon, 18 Apr 2011 17:43:16 GMT (envelope-from jhb@svn.freebsd.org) Received: (from jhb@localhost) by svn.freebsd.org (8.14.3/8.14.3/Submit) id p3IHhGBf079436; Mon, 18 Apr 2011 17:43:16 GMT (envelope-from jhb@svn.freebsd.org) Message-Id: <201104181743.p3IHhGBf079436@svn.freebsd.org> From: John Baldwin Date: Mon, 18 Apr 2011 17:43:16 +0000 (UTC) To: src-committers@freebsd.org, svn-src-all@freebsd.org, svn-src-head@freebsd.org X-SVN-Group: head MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Cc: Subject: svn commit: r220794 - head/sys/netinet X-BeenThere: svn-src-head@freebsd.org X-Mailman-Version: 2.1.5 Precedence: list List-Id: SVN commit messages for the src tree for head/-current List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Mon, 18 Apr 2011 17:43:17 -0000 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