Date: Sat, 10 Nov 2007 13:27:06 -0500 From: Gregory Wright <gwright@antiope.com> To: Andre Oppermann <andre@freebsd.org> Cc: freebsd-current@freebsd.org Subject: Re: excessive TCP dulplicate acks revisted Message-ID: <1AE5FE54-7677-48B3-AD7E-34F2D1569EA3@antiope.com> In-Reply-To: <4735CE3A.7020905@freebsd.org> References: <46B41421-3112-40C6-84D9-094FA771F93E@antiope.com> <4735CE3A.7020905@freebsd.org>
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On Nov 10, 2007, at 10:28 AM, Andre Oppermann wrote: > Gregory Wright wrote: >> (Note: long message) >> Hi, >> The tcp duplicate ACK attack is back. >> Last March, there was a thread on duplicate TCP acks in -CURRENT. >> I have been able to reproduce the problem on 7.0-BETA2 (amd64) >> and have some new information that might help locate the bug. >> Background: I first noticed problems with tcp connections dropping >> when Bacula was running on our backup server. The hardware was >> a dual Opteron 244, 2 GB RAM, running FreeBSD 6.2-RELEASE-p2. >> The ethernet NIC was a bge. >> We went through an extensive process to rule out hardware and cabling >> problems: the server hardware was replaced with a single Opteron 270 >> (dual core) on a Tyan S2882-D motherboard. The memory was replaced >> as well. The NICs are still bge. This machine is "hardtack". > > This may be a TSO bug in the bge hardware. Please repeat your > tests in > the original setup with TSO disabled on the bge interfaces > ("ifconfig bgeX -tso"). > Second if you've got another network card with something else than bge > please put it into the same box and run the tests as well. > > -- > Andre > Hi Andre, I turned off TSO on the bge interface and still had the low throughput. A packet log showed that there were still bursts of duplicate ACKs. Results of netperf from my PowerBook: crossroads-able> netperf -H hardtack TCP STREAM TEST from localhost (0.0.0.0) port 0 AF_INET to hardtack. 18clay.com (192.168.2.61) port 0 AF_INET Recv Send Send Socket Socket Message Elapsed Size Size Size Time Throughput bytes bytes bytes secs. 10^6bits/sec 65536 262144 262144 10.02 28.37 crossroads-able> The Tyan S2882-D motherboard has two bge interfaces and an fxp as well. Switching to the fxp interface, I get much better throughput: crossroads-able> netperf -H hardtack TCP STREAM TEST from localhost (0.0.0.0) port 0 AF_INET to hardtack. 18clay.com (192.168.2.61) port 0 AF_INET Recv Send Send Socket Socket Message Elapsed Size Size Size Time Throughput bytes bytes bytes secs. 10^6bits/sec 65536 262144 262144 10.02 93.70 crossroads-able> and the packet logs show no duplicate ACKs. I will run some longer tests to the fxp interface to verify that there are no problems. Greg
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