From owner-freebsd-net@FreeBSD.ORG Sat Nov 29 17:46:36 2008 Return-Path: Delivered-To: freebsd-net@freebsd.org Received: from mx1.freebsd.org (mx1.freebsd.org [IPv6:2001:4f8:fff6::34]) by hub.freebsd.org (Postfix) with ESMTP id 9680B1065678 for ; Sat, 29 Nov 2008 17:46:36 +0000 (UTC) (envelope-from dwmalone@maths.tcd.ie) Received: from salmon.maths.tcd.ie (salmon.maths.tcd.ie [IPv6:2001:770:10:300::86e2:510b]) by mx1.freebsd.org (Postfix) with SMTP id C0D508FC1E for ; Sat, 29 Nov 2008 17:46:35 +0000 (UTC) (envelope-from dwmalone@maths.tcd.ie) Received: from walton.maths.tcd.ie ([134.226.81.10] helo=walton.maths.tcd.ie) by salmon.maths.tcd.ie with SMTP id ; 29 Nov 2008 17:46:34 +0000 (GMT) Received: from localhost ([127.0.0.1] helo=maths.tcd.ie) by walton.maths.tcd.ie with SMTP id ; 29 Nov 2008 17:46:31 +0000 (GMT) To: Venkat Venkatsubra In-reply-to: Your message of "Sat, 29 Nov 2008 07:59:54 PST." <88524.13498.qm@web58307.mail.re3.yahoo.com> Date: Sat, 29 Nov 2008 17:46:30 +0000 From: David Malone Message-ID: <200811291746.aa88825@walton.maths.tcd.ie> Cc: Rui Paulo , freebsd-net@freebsd.org, Kevin Oberman Subject: Re: FreeBSD Window updates 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: Sat, 29 Nov 2008 17:46:36 -0000 I've got an example extract tcpdump of this at the end of the mail - here 6 ACKs are sent, 5 of which are pure window updates and several are 2us apart! I think the easy option is to delete the code that generates explicit window updates if the window moves by 2*MSS. We then should be doing something similar to Linux. The other easy alternative would be to add a sysclt that lets us generate an window update every N*MSS and by default set it to something big, like 10 or 100. That should effectively eliminate the updates during bulk data transfer, but may still generate some window updates after a loss. Normal ACKing for driving congestion control shouldn't be impacted by either of these suggested changes. David. 1227622713.276609 172.16.2.2.5002 > 172.16.1.51.39077: . ack 144097745 win 40798 (DF) 1227622713.276611 172.16.2.2.5002 > 172.16.1.51.39077: . ack 144097745 win 40830 (DF) 1227622713.276613 172.16.2.2.5002 > 172.16.1.51.39077: . ack 144097745 win 40862 (DF) 1227622713.276615 172.16.2.2.5002 > 172.16.1.51.39077: . ack 144097745 win 40894 (DF) 1227622713.276852 172.16.2.2.5002 > 172.16.1.51.39077: . ack 144097745 win 40926 (DF) 1227622713.276855 172.16.2.2.5002 > 172.16.1.51.39077: . ack 144097745 win 40958 (DF) 1227622713.296585 172.16.2.2.5002 > 172.16.1.51.39077: . ack 144100641 win 40956 (DF)