From owner-freebsd-current@FreeBSD.ORG Tue Feb 20 06:30:30 2007 Return-Path: X-Original-To: current@freebsd.org Delivered-To: freebsd-current@FreeBSD.ORG Received: from mx1.freebsd.org (mx1.freebsd.org [69.147.83.52]) by hub.freebsd.org (Postfix) with ESMTP id 7900A17366E for ; Tue, 20 Feb 2007 06:30:30 +0000 (UTC) (envelope-from andy@siliconlandmark.com) Received: from lexi.siliconlandmark.com (lexi.siliconlandmark.com [209.69.98.4]) by mx1.freebsd.org (Postfix) with ESMTP id 1A9FD13C428 for ; Tue, 20 Feb 2007 06:30:30 +0000 (UTC) (envelope-from andy@siliconlandmark.com) Received: from [10.0.1.5] (cpe-24-33-245-212.twmi.res.rr.com [24.33.245.212]) by lexi.siliconlandmark.com (8.13.8/8.13.3) with ESMTP id l1K6I8iU097496; Tue, 20 Feb 2007 01:18:09 -0500 (EST) (envelope-from andy@siliconlandmark.com) In-Reply-To: <17850.13146.266196.499166@grasshopper.cs.duke.edu> References: <17850.13146.266196.499166@grasshopper.cs.duke.edu> Mime-Version: 1.0 (Apple Message framework v752.3) Content-Type: text/plain; charset=US-ASCII; delsp=yes; format=flowed Message-Id: <2FE2BC67-A829-4BF9-B606-65DE1393E8DE@siliconlandmark.com> Content-Transfer-Encoding: 7bit From: Andre Guibert de Bruet Date: Tue, 20 Feb 2007 01:18:07 -0500 To: Andrew Gallatin X-Mailer: Apple Mail (2.752.3) X-Virus-Scanned: ClamAV 0.88.7/2609/Mon Feb 19 19:28:07 2007 on lexi.siliconlandmark.com X-Virus-Status: Clean X-Information: Please contact the ISP for more information X-SL-MailScanner: Not scanned: please contact your Internet E-Mail Service Provider for details X-SL-SpamCheck: not spam, SpamAssassin (not cached, score=0.061, required 6, AWL 0.61, BAYES_00 -2.60, RCVD_IN_SORBS_DUL 2.05, SPF_PASS -0.00) X-MailScanner-From: andy@siliconlandmark.com Cc: current@freebsd.org Subject: Re: excessive TCP duplicate acks? X-BeenThere: freebsd-current@freebsd.org X-Mailman-Version: 2.1.5 Precedence: list List-Id: Discussions about the use of FreeBSD-current List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Tue, 20 Feb 2007 06:30:30 -0000 On Jan 26, 2007, at 11:59 AM, Andrew Gallatin wrote: > When running some benchmarks, I noticed tons of duplicate acks showing > up in systat -tcp (thousands, or tens of thousands per second). > Taking a trace, I see that -current seems to send "lots" of duplicate > acks. At first I thought this was a driver bug, but I've seen it with > 3 different drivers (mxge, nve, xl) and at various network speeds. It > seems to happen when the -current machine is the "sender" in a > netperf, and seems to happen with both a linux a FreeBSD receiver, > and is easy to reproduce using -current from yesterday (running > on amd64 if it matters). > >> From my very naive tcpdump reading skills, it looks like the FreeBSD > machine sends a full window with a partial payload and a push flag in > the last segment. It ignores (or does not yet see the receiver's > acks). It then spews tons of duplicate acks at the reciever until it > notices the acks, and starts sending data again. This happens over > and over again.. > > Is this normal, or is there something wrong? > > In the appended tcpdump snippet taken at the receiver, 172.31.193.16 > was sending a netperf (netperf -H172.31.193.15 -- -s65535 -S32767) to > 172.31.193.15. I can make a raw dump file available if anybody > is interested. > > <..many packets omitted..> I saw this behavior on an Intel gigabit NIC (em driver) with a kernel from January 22nd. This problem still persists with a kernel from today. Enabling/Disabling tx/rxcsum doesn't help. Machine details can be found up at http://bling.properkernel.com/ freebsd/ (Which is incidentally the machine that is seeing these issues). If you would like to see just what kind of traffic patterns I am seeing, load up wireshark / tcpdump and download one of the freebsd release images on the webserver. uname -a: FreeBSD bling.properkernel.com 7.0-CURRENT FreeBSD 7.0- CURRENT #8: Mon Feb 19 16:21:52 EST 2007 andy@bling.properkernel.com:/usr/obj/usr/src/sys/BLING i386 Andy /* Andre Guibert de Bruet * 6f43 6564 7020 656f 2e74 4220 7469 6a20 */ /* Code poet / Sysadmin * 636f 656b 2e79 5320 7379 6461 696d 2e6e */ /* GSM: +1 734 846 8758 * 5520 494e 2058 6c73 7565 6874 002e 0000 */ /* WWW: siliconlandmark.com * C/C++, Java, Perl, PHP, SQL, XHTML, XML */