From mboxrd@z Thu Jan 1 00:00:00 1970 From: Lucas Nussbaum Subject: Re: [PATCH] tcp_cubic: enable TCP timestamps Date: Tue, 8 Mar 2011 20:36:02 +0100 Message-ID: <20110308193602.GA14526@xanadu.blop.info> References: <20110308080926.GA22641@xanadu.blop.info> <20110308104211.3567526f@nehalam> <20110308.105503.104060436.davem@davemloft.net> Mime-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Transfer-Encoding: QUOTED-PRINTABLE Cc: David Miller , shemminger@vyatta.com, netdev@vger.kernel.org To: Sangtae Ha Return-path: Received: from xanadu.blop.info ([178.79.145.134]:48679 "EHLO xanadu.blop.info" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754669Ab1CHTfM (ORCPT ); Tue, 8 Mar 2011 14:35:12 -0500 Content-Disposition: inline In-Reply-To: Sender: netdev-owner@vger.kernel.org List-ID: On 08/03/11 at 14:15 -0500, Sangtae Ha wrote: > Yes. I remember that CONFIG_HZ was 1000 at that time and the value of > CONFIG_HZ could affect the algorithm. > I don't think HyStart needs this extra RTT_STAMP since we only need a > rough delay estimate. > Let me check HyStart with the latest git and with different CONFIG_HZ= values. One of the problems I discovered was that ca->delay_min was completely off if RTT_STAMP is disabled. For example, on a link with a 11ms RTT, I could get delay_min =3D 4ms. But even with RTT_STAMP, there's the probl= em that the code rounds the computed RTT value to a jiffie (in bictcp_acked()). My other patch mitigates the performance problem by making it harder fo= r Hystart to abort slow start. But after a few days working on this issue= , I'm wondering whether Hystart shouldn't be completely rewritten to work on the usec values, or disabled by default. --=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 |