From mboxrd@z Thu Jan 1 00:00:00 1970 From: Ben Greear Subject: Re: Question on TSO maximum segment sizes. Date: Thu, 11 Oct 2007 17:17:48 -0700 Message-ID: <470EBD2C.8020704@candelatech.com> References: <20071011.163737.36654032.davem@davemloft.net><470EB6D6.9020704@hp.com> <20071011.170244.32082446.davem@davemloft.net> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Cc: David Miller , rick.jones2@hp.com, netdev@vger.kernel.org To: "Waskiewicz Jr, Peter P" Return-path: Received: from ns2.lanforge.com ([66.165.47.211]:35864 "EHLO ns2.lanforge.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753292AbXJLAR5 (ORCPT ); Thu, 11 Oct 2007 20:17:57 -0400 In-Reply-To: Sender: netdev-owner@vger.kernel.org List-Id: netdev.vger.kernel.org Waskiewicz Jr, Peter P wrote: >> From: Rick Jones >> Date: Thu, 11 Oct 2007 16:50:46 -0700 >> >>> For just messing about, might it be possible to tweak the socket >>> buffer sizes and tcp_tso_win_divisor to kludge things for a short >>> while? Couldn't ship that way certainly, but assuming >> Peter's going >>> to get his broken hardware fixed it might let him limp >> along until then. >> >> TCP dynamically grows the socket buffer sizes unless the >> application explicitly sets them via setsockopt() and the >> limits imposed in those cases are controlled by >> tcp_{,r,w}mem[] sysctls. Decreasing those will kill >> performance exactly for the cases this person cares about. I just tried turning off my explicit SO_SNDBUF/SO_RCVBUG settings in my app, and the connection ran very poorly through a link with even a small bit of latency (~2-4ms I believe). It ran near gige line speed through a cross-over cable. I have the sysctl max values set very generous, though the min and default are fairly small. This was with kernel 2.6.20. Was the auto-tuning put in after 2.6.20? If not, has this been tested through a higher latency link? Or, am I confused and you are talking about some other setsockopt? Thanks, Ben -- Ben Greear Candela Technologies Inc http://www.candelatech.com