From owner-freebsd-net@FreeBSD.ORG Wed Aug 14 02:45:46 2013 Return-Path: Delivered-To: net@freebsd.org Received: from mx1.freebsd.org (mx1.freebsd.org [IPv6:2001:1900:2254:206a::19:1]) (using TLSv1 with cipher ADH-AES256-SHA (256/256 bits)) (No client certificate requested) by hub.freebsd.org (Postfix) with ESMTP id 768E86D3; Wed, 14 Aug 2013 02:45:46 +0000 (UTC) (envelope-from lstewart@freebsd.org) Received: from lauren.room52.net (lauren.room52.net [210.50.193.198]) by mx1.freebsd.org (Postfix) with ESMTP id 39D3C27D1; Wed, 14 Aug 2013 02:45:46 +0000 (UTC) Received: from lstewart.caia.swin.edu.au (lstewart.caia.swin.edu.au [136.186.229.95]) by lauren.room52.net (Postfix) with ESMTPSA id 90A2E7E88D; Wed, 14 Aug 2013 12:36:31 +1000 (EST) Message-ID: <520AED2F.4050001@freebsd.org> Date: Wed, 14 Aug 2013 12:36:31 +1000 From: Lawrence Stewart User-Agent: Mozilla/5.0 (X11; FreeBSD amd64; rv:17.0) Gecko/20130801 Thunderbird/17.0.7 MIME-Version: 1.0 To: Andre Oppermann Subject: TCP Initial Window 10 MFC (was: Re: svn commit: r252789 - stable/9/sys/netinet) References: <201307051458.r65EwObo066269@svn.freebsd.org> In-Reply-To: <201307051458.r65EwObo066269@svn.freebsd.org> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-Spam-Status: No, score=0.0 required=5.0 tests=UNPARSEABLE_RELAY autolearn=unavailable version=3.3.2 X-Spam-Checker-Version: SpamAssassin 3.3.2 (2011-06-06) on lauren.room52.net Cc: "freebsd-net@freebsd.org" X-BeenThere: freebsd-net@freebsd.org X-Mailman-Version: 2.1.14 Precedence: list List-Id: Networking and TCP/IP with FreeBSD List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Wed, 14 Aug 2013 02:45:46 -0000 Hi Andre, [RE team is BCCed so they're aware of this discussion] On 07/06/13 00:58, Andre Oppermann wrote: > Author: andre > Date: Fri Jul 5 14:58:24 2013 > New Revision: 252789 > URL: http://svnweb.freebsd.org/changeset/base/252789 > > Log: > MFC r242266: > > Increase the initial CWND to 10 segments as defined in IETF TCPM > draft-ietf-tcpm-initcwnd-05. It explains why the increased initial > window improves the overall performance of many web services without > risking congestion collapse. > > As long as it remains a draft it is placed under a sysctl marking it > as experimental: > net.inet.tcp.experimental.initcwnd10 = 1 > When it becomes an official RFC soon the sysctl will be changed to > the RFC number and moved to net.inet.tcp. > > This implementation differs from the RFC draft in that it is a bit > more conservative in the case of packet loss on SYN or SYN|ACK because > we haven't reduced the default RTO to 1 second yet. Also the restart > window isn't yet increased as allowed. Both will be adjusted with > upcoming changes. > > Is is enabled by default. In Linux it is enabled since kernel 3.0. I haven't been fully alert to FreeBSD happenings this year so apologies for bringing this up so long after the MFC. I don't think this change should have been MFCed, at least not in its current form. Enabling the switch to IW=10 on a stable branch is inappropriate IMO. I also think the "net.inet.tcp.experimental" sysctl branch is poorly named as per the important discussion we had back in February [1]. I would really prefer we didn't get stuck having to keep it around by making a stable release with it being present. I think this commit should be backed out of stable/9 and more importantly, 9.2-RELEASE. As an aside, I am intending to follow up to the Feb discussion with a patch that implements the basic infrastructure I proposed so that we can continue that discussion. Thoughts? Cheers, Lawrence [1] http://lists.freebsd.org/pipermail/freebsd-net/2013-February/034698.html