From owner-freebsd-net@FreeBSD.ORG Wed Feb 6 13:16:52 2013 Return-Path: Delivered-To: net@freebsd.org Received: from mx1.freebsd.org (mx1.freebsd.org [IPv6:2001:1900:2254:206a::19:1]) by hub.freebsd.org (Postfix) with ESMTP id E7721DF9 for ; Wed, 6 Feb 2013 13:16:52 +0000 (UTC) (envelope-from jhb@freebsd.org) Received: from bigwig.baldwin.cx (bigknife-pt.tunnel.tserv9.chi1.ipv6.he.net [IPv6:2001:470:1f10:75::2]) by mx1.freebsd.org (Postfix) with ESMTP id 3940C943 for ; Wed, 6 Feb 2013 13:16:52 +0000 (UTC) Received: from pakbsde14.localnet (unknown [38.105.238.108]) by bigwig.baldwin.cx (Postfix) with ESMTPSA id 73BD1B911; Wed, 6 Feb 2013 08:16:51 -0500 (EST) From: John Baldwin To: Randall Stewart Subject: Re: [PATCH] Add a new TCP_IGNOREIDLE socket option Date: Wed, 6 Feb 2013 07:46:43 -0500 User-Agent: KMail/1.13.5 (FreeBSD/8.2-CBSD-20110714-p22; KDE/4.5.5; amd64; ; ) References: <201301221511.02496.jhb@freebsd.org> <50FF06AD.402@networx.ch> <061B4EA5-6A93-48A0-A269-C2C3A3C7E77C@lakerest.net> In-Reply-To: <061B4EA5-6A93-48A0-A269-C2C3A3C7E77C@lakerest.net> MIME-Version: 1.0 Content-Type: Text/Plain; charset="iso-8859-1" Content-Transfer-Encoding: 7bit Message-Id: <201302060746.43736.jhb@freebsd.org> X-Greylist: Sender succeeded SMTP AUTH, not delayed by milter-greylist-4.2.7 (bigwig.baldwin.cx); Wed, 06 Feb 2013 08:16:51 -0500 (EST) Cc: Alfred Perlstein , 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, 06 Feb 2013 13:16:53 -0000 On Wednesday, February 06, 2013 6:27:04 am Randall Stewart wrote: > John: > > A burst at line rate will *often* cause drops. This is because > router queues are at a finite size. Also such a burst (especially > on a long delay bandwidth network) cause your RTT to increase even > if there is no drop which is going to hurt you as well. > > A SHOULD in an RFC says you really really really really need to do it > unless there is some thing that makes you willing to override it. It is > slight wiggle room. > > In this I agree with Andre, we should not be *not* doing it. Otherwise > folks will be turning this on and it is plain wrong. It may be fine > for your network but I would not want to see it in FreeBSD. > > In my testing here at home I have put back into our stack max-burst. This > uses Mark Allman's version (not Kacheong Poon's) where you clamp the cwnd at > no more than 4 packets larger than your flight. All of my testing > high-bw-delay or lan has shown this to improve TCP performance. This > is because it helps you avoid bursting out so many packets that you overflow > a queue. > > In your long-delay bw link if you do burst out too many (and you never > know how many that is since you can not predict how full all those > MPLS queues are or how big they are) you will really hurt yourself even worse. > Note that generally in Cisco routers the default queue size is somewhere between > 100-300 packets depending on the router. Due to the way our application works this never happens, but I am fine with just keeping this patch private. If there are other shops that need this they can always dig the patch up from the archives. -- John Baldwin