From owner-freebsd-net@FreeBSD.ORG Mon Jul 16 11:02:17 2007 Return-Path: X-Original-To: freebsd-net@freebsd.org Delivered-To: freebsd-net@freebsd.org Received: from mx1.freebsd.org (mx1.freebsd.org [69.147.83.52]) by hub.freebsd.org (Postfix) with ESMTP id A265916A404 for ; Mon, 16 Jul 2007 11:02:17 +0000 (UTC) (envelope-from rrs@cisco.com) Received: from sj-iport-5.cisco.com (sj-iport-5.cisco.com [171.68.10.87]) by mx1.freebsd.org (Postfix) with ESMTP id 7B67313C4AA for ; Mon, 16 Jul 2007 11:02:17 +0000 (UTC) (envelope-from rrs@cisco.com) Received: from sj-dkim-3.cisco.com ([171.71.179.195]) by sj-iport-5.cisco.com with ESMTP; 16 Jul 2007 04:02:17 -0700 X-IronPort-Anti-Spam-Filtered: true X-IronPort-Anti-Spam-Result: Ao8CAI7smkarR7PD/2dsb2JhbAA X-IronPort-AV: i="4.16,541,1175497200"; d="scan'208"; a="166761018:sNHT26814114" Received: from sj-core-1.cisco.com (sj-core-1.cisco.com [171.71.177.237]) by sj-dkim-3.cisco.com (8.12.11/8.12.11) with ESMTP id l6GB2GpY004548; Mon, 16 Jul 2007 04:02:16 -0700 Received: from xbh-sjc-211.amer.cisco.com (xbh-sjc-211.cisco.com [171.70.151.144]) by sj-core-1.cisco.com (8.12.10/8.12.6) with ESMTP id l6GB2GA0023338; Mon, 16 Jul 2007 11:02:16 GMT Received: from xfe-sjc-212.amer.cisco.com ([171.70.151.187]) by xbh-sjc-211.amer.cisco.com with Microsoft SMTPSVC(6.0.3790.1830); Mon, 16 Jul 2007 04:02:16 -0700 Received: from [127.0.0.1] ([171.68.225.134]) by xfe-sjc-212.amer.cisco.com with Microsoft SMTPSVC(6.0.3790.1830); Mon, 16 Jul 2007 04:02:15 -0700 Message-ID: <469B5069.6080706@cisco.com> Date: Mon, 16 Jul 2007 07:03:05 -0400 From: Randall Stewart User-Agent: Mozilla/5.0 (X11; U; FreeBSD i386; en-US; rv:1.7.13) Gecko/20070601 X-Accept-Language: en-us, en MIME-Version: 1.0 To: James Healy References: <469AF916.6090901@swin.edu.au> <469AFE80.2090304@swin.edu.au> In-Reply-To: <469AFE80.2090304@swin.edu.au> Content-Type: text/plain; charset=us-ascii; format=flowed Content-Transfer-Encoding: 7bit X-OriginalArrivalTime: 16 Jul 2007 11:02:15.0901 (UTC) FILETIME=[C51850D0:01C7C798] DKIM-Signature: v=0.5; a=rsa-sha256; q=dns/txt; l=1183; t=1184583736; x=1185447736; c=relaxed/simple; s=sjdkim3002; h=Content-Type:From:Subject:Content-Transfer-Encoding:MIME-Version; d=cisco.com; i=rrs@cisco.com; z=From:=20Randall=20Stewart=20 |Subject:=20Re=3A=20Odd=20congestion=20window=20behaviour=20[=20was=3A=20 Draft=20email=20to=20freebsd-net=0A=20] |Sender:=20; bh=dMvzzWh4XbuU22scbtqdY36V3ZsV0BnwYLcduPltK+4=; b=dt90a36XV4NApPPOWVRWLxi95K+frLMorkUx5LotlNaq72TrX3qirENe7COV+NClSAtuFn2x d+XEXm+BWXMHaeoECnbHMd3ScjSkpx+NPgmVCH2vm9uAEdlawbtjWmLI; Authentication-Results: sj-dkim-3; header.From=rrs@cisco.com; dkim=pass (sig from cisco.com/sjdkim3002 verified; ); Cc: freebsd-net@freebsd.org, Andrew , Lawrence Stewart Subject: Re: Odd congestion window behaviour [ was: Draft email to freebsd-net ] X-BeenThere: freebsd-net@freebsd.org X-Mailman-Version: 2.1.5 Precedence: list List-Id: Networking and TCP/IP with FreeBSD List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Mon, 16 Jul 2007 11:02:17 -0000 James Healy wrote: >>This behaviour seems a little odd to us - can anyone shed some light on >>it? Our assumption is that the use of the hostcache is designed to >>increase performance where appropriate by seeding the initial cwnd based >>on past experience. >> >>For this section of code to return a cwnd that is successfully >>influenced by the hostcache, it would seem that the use of tp->snd_wnd >>should be avoided when the connection is still being initialised: >> Oh, one other comment I have on this.. This is the code that used to be buried with comments about Alman et.al. says this is ok to do... if I am remembering right... I.e. where we keep past connection state and use that as a reference for the initial cwnd. I asked Mark about this in the past.. and he said that his paper was mis-interpreted and this is incorrect behavior. If you have no connections up to a peer you should not use any past value for the cwnd... Thats why we don't do it in SCTP. I know a lot of O/S's do this.. but it is not sanctified IMO from the CC experts :-D R -- Randall Stewart NSSTG - Cisco Systems Inc. 803-345-0369 803-317-4952 (cell)