From owner-freebsd-net@FreeBSD.ORG Tue Jul 17 12:24:50 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 AE14316A400 for ; Tue, 17 Jul 2007 12:24:50 +0000 (UTC) (envelope-from jhealy@groupwise.swin.edu.au) Received: from mailmonitor.cc.swin.edu.au (mailmonitor.cc.swin.edu.au [136.186.1.65]) by mx1.freebsd.org (Postfix) with ESMTP id 2113713C4B8 for ; Tue, 17 Jul 2007 12:24:49 +0000 (UTC) (envelope-from jhealy@groupwise.swin.edu.au) Received: from groupwise.swin.edu.au (Not Verified[136.186.3.218]) by mailmonitor.cc.swin.edu.au with MailMarshal (v6, 1, 4, 441) id ; Tue, 17 Jul 2007 22:04:32 +1000 Received: from INET-DOM-MTA by groupwise.swin.edu.au with Novell_GroupWise; Tue, 17 Jul 2007 22:04:32 +1000 Message-Id: <469D3CE1020000B70000F83B@groupwise.swin.edu.au> X-Mailer: Novell GroupWise Internet Agent 7.0.1 Date: Tue, 17 Jul 2007 22:04:17 +1000 From: "James Healy" To: , Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Content-Disposition: inline Cc: andybrand@swin.edu.au 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: Tue, 17 Jul 2007 12:24:50 -0000 >>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... > > So it's possible that the inital cwnd shouldn't be set by the hostcache > at all? > > If this was the case, does that mean we'd just use the rfc 3390 logic if > enabled, with fallback to the manual sysctl variables as a last resort? I haven't tested it yet, but I just noticed that initial odd behaviour we observed looks like it's been fixed in tcp_input.c revisions 1.315 (MAIN) / 1.281.2.13 (RELENG_6). It ensures that tp->snd_wnd is initialised before being used to calculate the initial cwnd. The follow on question about setting cwnd from the hostcache still stands I guess, but at least with this fix we won't see transmission delays while the connection waits for a delayed ack timer to expire. James Swinburne University of Technology CRICOS Provider Code: 00111D NOTICE This e-mail and any attachments are confidential and intended only for the use of the addressee. They may contain information that is privileged or protected by copyright. If you are not the intended recipient, any dissemination, distribution, printing, copying or use is strictly prohibited. The University does not warrant that this e-mail and any attachments are secure and there is also a risk that it may be corrupted in transmission. It is your responsibility to check any attachments for viruses or defects before opening them. If you have received this transmission in error, please contact us on +61 3 9214 8000 and delete it immediately from your system. We do not accept liability in connection with computer virus, data corruption, delay, interruption, unauthorised access or unauthorised amendment. Please consider the environment before printing this email.