From mboxrd@z Thu Jan 1 00:00:00 1970 From: Stephen Hemminger Subject: Re: TCP congestion graphs (2.6.19-rc4) Date: Tue, 31 Oct 2006 16:10:07 -0800 Message-ID: <20061031161007.0fdf5c63@freekitty> References: <20061025110207.78d38779@freekitty> <000701c6f885$b57aa390$4a580e98@ncsu2cc0c3fa00> <20061031120016.75dc4c3c@freekitty> <7335583a0610311525h10cf4e75x42e421d3eb6f53aa@mail.gmail.com> Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Cc: "Injong Rhee" , "David S. Miller" , "Sangtae Ha" , netdev@vger.kernel.org Return-path: Received: from smtp.osdl.org ([65.172.181.4]:65483 "EHLO smtp.osdl.org") by vger.kernel.org with ESMTP id S1946215AbWKAAKS (ORCPT ); Tue, 31 Oct 2006 19:10:18 -0500 To: "Xiaoliang (David) Wei" In-Reply-To: <7335583a0610311525h10cf4e75x42e421d3eb6f53aa@mail.gmail.com> Sender: netdev-owner@vger.kernel.org List-Id: netdev.vger.kernel.org On Tue, 31 Oct 2006 15:25:16 -0800 "Xiaoliang (David) Wei" wrote: > 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 > I ran with the current default: alpha = 1 (scaled 2) beta = 3 (scaled 6) gamma = 1 (scaled 2) -- Stephen Hemminger