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 07:53:19 +0100 Message-ID: <20110309065319.GA23740@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> Mime-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Transfer-Encoding: QUOTED-PRINTABLE Cc: Stephen Hemminger , David Miller , xiyou.wangcong@gmail.com, netdev@vger.kernel.org, sangtae.ha@gmail.com To: Injong Rhee Return-path: Received: from xanadu.blop.info ([178.79.145.134]:38962 "EHLO xanadu.blop.info" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751514Ab1CIGwb (ORCPT ); Wed, 9 Mar 2011 01:52:31 -0500 Content-Disposition: inline In-Reply-To: <4D76D851.4050600@ncsu.edu> Sender: netdev-owner@vger.kernel.org List-ID: 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. --=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 |