From mboxrd@z Thu Jan 1 00:00:00 1970 From: Stephen Hemminger Subject: Re: [PATCH] Make CUBIC Hystart more robust to RTT variations Date: Wed, 9 Mar 2011 09:56:59 -0800 Message-ID: <20110309095659.1373c296@s6510> References: <20110308111011.GA27967@xanadu.blop.info> <4D764AAC.30302@ncsu.edu> <20110308.114346.48506864.davem@davemloft.net> <20110308152103.714f5f05@nehalam> <4D76D851.4050600@ncsu.edu> <20110309065319.GA23740@xanadu.blop.info> Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Cc: Injong Rhee , David Miller , xiyou.wangcong@gmail.com, netdev@vger.kernel.org, sangtae.ha@gmail.com To: Lucas Nussbaum Return-path: Received: from mail.vyatta.com ([76.74.103.46]:35182 "EHLO mail.vyatta.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1757128Ab1CIR5D (ORCPT ); Wed, 9 Mar 2011 12:57:03 -0500 In-Reply-To: <20110309065319.GA23740@xanadu.blop.info> Sender: netdev-owner@vger.kernel.org List-ID: On Wed, 9 Mar 2011 07:53:19 +0100 Lucas Nussbaum wrote: > On 08/03/11 at 20:30 -0500, Injong Rhee wrote: > > Now, both tools can be wrong. But that is not catastrophic since > > congestion avoidance can kick in to save the day. In a pipe where no > > other flows are competing, then exiting slow start too early can > > slow things down as the window can be still too small. But that is > > in fact when delays are most reliable. So those tests that say bad > > performance with hystart are in fact, where hystart is supposed to > > perform well. > > Hi, > > In my setup, there is no congestion at all (except the buffer bloat). > Without Hystart, transferring 8 Gb of data takes 9s, with CUBIC exiting > slow start at ~2000 packets. > With Hystart, transferring 8 Gb of data takes 19s, with CUBIC exiting > slow start at ~20 packets. > I don't think that this is "hystart performing well". We could just as > well remove slow start completely, and only do congestion avoidance, > then. > > While I see the value in Hystart, it's clear that there are some flaws > in the current implementation. It probably makes sense to disable > hystart by default until those problems are fixed. What is the speed and RTT time of your network? I think you maybe blaming hystart for other issues in the network.