From mboxrd@z Thu Jan 1 00:00:00 1970 From: "Xiaoliang (David) Wei" Subject: Re: TCP congestion graphs (2.6.19-rc4) Date: Tue, 31 Oct 2006 15:25:16 -0800 Message-ID: <7335583a0610311525h10cf4e75x42e421d3eb6f53aa@mail.gmail.com> References: <20061025110207.78d38779@freekitty> <000701c6f885$b57aa390$4a580e98@ncsu2cc0c3fa00> <20061031120016.75dc4c3c@freekitty> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Cc: "Injong Rhee" , "David S. Miller" , "Sangtae Ha" , netdev@vger.kernel.org Return-path: Received: from nz-out-0102.google.com ([64.233.162.198]:8883 "EHLO nz-out-0102.google.com") by vger.kernel.org with ESMTP id S1946155AbWJaXZR (ORCPT ); Tue, 31 Oct 2006 18:25:17 -0500 Received: by nz-out-0102.google.com with SMTP id z3so1601474nzf for ; Tue, 31 Oct 2006 15:25:16 -0800 (PST) To: "Stephen Hemminger" In-Reply-To: <20061031120016.75dc4c3c@freekitty> Content-Disposition: inline Sender: netdev-owner@vger.kernel.org List-Id: netdev.vger.kernel.org On 10/31/06, Stephen Hemminger wrote: > I reran the tests, this time using my DSL line to home (80ms 1Mbit/sec). > http://developer.osdl.org/shemminger/tcp/2.6.19-rc4/dsl > > The only obvious problem is Vegas looks broken. Thanks, Stephen. It seems that the default Vegas alpha parameter in the rc4 is 1... I observed similar situation with the NS2Linux simulator (with 2.6.16 code) and found that if alpha=1, delayed ack will make it broken (keeping cwnd very low without real congestion) See details at http://www.cs.caltech.edu/%7Eweixl/technical/ns2linux/known_linux/index.html#vegas (Basically alpha==1 means Vegas seeks to see a delay of about 1 packet worth. With delayed ack, 1 packet worth of delay is common even with no congestion.) To make Vegas work, I'd suggest to raise alpha to at least 2 or 3. (and beta has to be at least as large as alpha.) -David -- Xiaoliang (David) Wei Graduate Student, CS@Caltech http://davidwei.org ***********************************************