Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1422626AbWKHT2Y (ORCPT ); Wed, 8 Nov 2006 14:28:24 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1161721AbWKHT2X (ORCPT ); Wed, 8 Nov 2006 14:28:23 -0500 Received: from mga05.intel.com ([192.55.52.89]:53766 "EHLO fmsmga101.fm.intel.com") by vger.kernel.org with ESMTP id S1161694AbWKHT2V (ORCPT ); Wed, 8 Nov 2006 14:28:21 -0500 X-ExtLoop1: 1 X-IronPort-AV: i="4.09,401,1157353200"; d="scan'208"; a="13405789:sNHT19614699" Subject: Re: 2.6.19-rc1: Volanomark slowdown From: Tim Chen Reply-To: tim.c.chen@linux.intel.com To: Olaf Kirch Cc: Arjan van de Ven , linux-kernel@vger.kernel.org, davem@sunset.davemloft.net, kuznet@ms2.inr.ac.ru, netdev@vger.kernel.org In-Reply-To: <20061108162955.GA4364@suse.de> References: <1162924354.10806.172.camel@localhost.localdomain> <1163001318.3138.346.camel@laptopd505.fenrus.org> <20061108162955.GA4364@suse.de> Content-Type: text/plain Organization: Intel Date: Wed, 08 Nov 2006 10:38:52 -0800 Message-Id: <1163011132.10806.189.camel@localhost.localdomain> Mime-Version: 1.0 X-Mailer: Evolution 2.0.2 (2.0.2-8) Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1385 Lines: 33 On Wed, 2006-11-08 at 17:29 +0100, Olaf Kirch wrote: > Is it proven that the number of ACKs actually cause bandwidth problems? > I found Volanomark to exercise the scheduler more than anything else, > so maybe the slowdown, while triggered by an increased number of ACKs, > is caused by something else entirely. > The patch in question affects purely TCP and not the scheduler. I don't think the scheduler has anything to do with the slowdown seen after the patch is applied. The total number of messages being exchanged around the chatrooms in Volanomark remain unchanged. But ACKS increase by 3.5 times and segments received increase by 38% from netstat. ACK is comparable in size to the actual Volanomark messages as those are pretty small (<100 byte). So I think it is reasonable to conclude that the increase in TCP traffic reduce the bandwidth and throughput in Volanomark. However, Volanomark is just a benchmark to alert us to changes. If in real applications with small segment, this patch is needed to fix congestion window adjustment as Dave pointed out, and impact on bandwidth not as important, so be it. Tim - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/