Re: excessive TCP dulplicate acks revisted
- From: Gregory Wright <gwright@xxxxxxxxxxx>
- Date: Sat, 10 Nov 2007 13:27:06 -0500
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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- From: Gregory Wright
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