From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S262192AbTD3PSe (ORCPT ); Wed, 30 Apr 2003 11:18:34 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S262277AbTD3PSe (ORCPT ); Wed, 30 Apr 2003 11:18:34 -0400 Received: from fluent2.pyramid.net ([206.100.220.213]:28322 "EHLO fluent2.pyramid.net") by vger.kernel.org with ESMTP id S262192AbTD3PSd (ORCPT ); Wed, 30 Apr 2003 11:18:33 -0400 X-Not-Legal-Opinion: IANAL I am not a lawyer X-For-Entertainment-Purposes-Only: True Message-Id: <5.2.0.9.0.20030430082756.00a73730@fluent2.pyramid.net> X-Mailer: QUALCOMM Windows Eudora Version 5.2.0.9 Date: Wed, 30 Apr 2003 08:30:51 -0700 To: Shesha@asu.edu, linux-kernel@vger.kernel.org, kernelnewbies@nl.linux.org From: Stephen Satchell Subject: Re: Why throughput increases as MTU size is increased In-Reply-To: Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii"; format=flowed Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org At 07:10 AM 4/30/03 -0700, Shesha@asu.edu wrote: > When I measure the performance of iSCSI on XScale with MTU size = 1500 > bytes, >a throughput of 32 Mbps was observed. As the MTU size was increased, the >throughput also increased. >1500 -> 32 Mbps >3000 -> 56 >4500 -> 80 >6000 -> 100 >7500 -> 108 >9000 -> 108 The non-linear increase as you change MTU is the dead give-away: the slow-start algorithm is working just fine. The reason you didn't get double the throughput as you doubled the MTU is that the slow-start algorithm ramps based on packet count, so as you increase the MTU the packet rate slope remains reasonably constant. If you have the source code, you can turn off slow-start using setsocketopt(), and see what happens. Have you considered trying a longer file? -- X -> unknown; Spurt -> drip of water under pressure Expert -> X-Spurt -> Unknown drip under pressure.