From mboxrd@z Thu Jan 1 00:00:00 1970 From: Lucas Nussbaum Subject: Re: [PATCH] Make CUBIC Hystart more robust to RTT variations Date: Wed, 9 Mar 2011 19:25:05 +0100 Message-ID: <20110309182505.GA25272@xanadu.blop.info> 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> <20110309095659.1373c296@s6510> Mime-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Transfer-Encoding: QUOTED-PRINTABLE Cc: Injong Rhee , David Miller , xiyou.wangcong@gmail.com, netdev@vger.kernel.org, sangtae.ha@gmail.com To: Stephen Hemminger Return-path: Received: from xanadu.blop.info ([178.79.145.134]:43487 "EHLO xanadu.blop.info" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752244Ab1CIS1i (ORCPT ); Wed, 9 Mar 2011 13:27:38 -0500 Content-Disposition: inline In-Reply-To: <20110309095659.1373c296@s6510> Sender: netdev-owner@vger.kernel.org List-ID: On 09/03/11 at 09:56 -0800, Stephen Hemminger wrote: > On Wed, 9 Mar 2011 07:53:19 +0100 > Lucas Nussbaum wrote: >=20 > > 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 i= s > > > in fact when delays are most reliable. So those tests that say ba= d > > > performance with hystart are in fact, where hystart is supposed t= o > > > perform well. > >=20 > > Hi, > >=20 > > In my setup, there is no congestion at all (except the buffer bloat= ). > > Without Hystart, transferring 8 Gb of data takes 9s, with CUBIC exi= ting > > slow start at ~2000 packets. > > With Hystart, transferring 8 Gb of data takes 19s, with CUBIC exiti= ng > > 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. > >=20 > > While I see the value in Hystart, it's clear that there are some fl= aws > > in the current implementation. It probably makes sense to disable > > hystart by default until those problems are fixed. >=20 > What is the speed and RTT time of your network? > I think you maybe blaming hystart for other issues in the network. What kind of issues? Host1 is connected through a gigabit ethernet LAN to Router1 Host2 is connected through a gigabit ethernet LAN to Router2 Router1 and Router2 are connected through an experimentation network at 10 Gb/s RTT between Host1 and Host2 is 11.3ms. The network is not congested. (I can provide access to the testbed if someone wants to do further testing) --=20 | Lucas Nussbaum MCF Universit=E9 Nancy 2 | | lucas.nussbaum@loria.fr LORIA / AlGorille | | http://www.loria.fr/~lnussbau/ +33 3 54 95 86 19 |