From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S262179AbTD3N5s (ORCPT ); Wed, 30 Apr 2003 09:57:48 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S262182AbTD3N5r (ORCPT ); Wed, 30 Apr 2003 09:57:47 -0400 Received: from post2.inre.asu.edu ([129.219.110.73]:54256 "EHLO post2.inre.asu.edu") by vger.kernel.org with ESMTP id S262179AbTD3N5q (ORCPT ); Wed, 30 Apr 2003 09:57:46 -0400 Date: Wed, 30 Apr 2003 07:10:04 -0700 (MST) From: Shesha@asu.edu Subject: Why throughput increases as MTU size is increased To: linux-kernel@vger.kernel.org, kernelnewbies@nl.linux.org Message-id: MIME-version: 1.0 Content-type: TEXT/PLAIN; charset=US-ASCII Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Hi All, I have a question which I am not able to answer myself.I request you all to give me some input. 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 Actually the throughput saturates. I thought, the per-packet overhead decreases as the MTU size increases. This contributes to the performance improvement. And the saturation is achieved because, the iSCSI max PDU size is 8k. Even if we increase the MTU size beyond 8k, we will not see any change because, iSCSI devivers a max of 8K PDU to TCP. Therefore a saturation in throughput is observed. But the question is, Am I thinking correctly? secondly, if yes,does the per-packet over head decrease the performance so much. we are observing, somewhere like 4 times improvement in throughput. Can there be any other reason for this observation. Thanking you Shesha