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List:       openvswitch-discuss
Subject:    [ovs-discuss] Simple test-setup: lots of TCP Retransmission, TCP Dup ACK
From:       hans.van.kranenburg () mendix ! com (Hans van Kranenburg)
Date:       2012-01-23 22:01:43
Message-ID: 4F1DD8C7.2010805 () mendix ! com
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Don't want to revive the thread, but just for the sake of completeness:

On 01/09/2012 09:01 PM, Jesse Gross wrote:
> On Sun, Jan 8, 2012 at 1:01 PM, Hans van Kranenburg
> <hans.van.kranenburg at mendix.com> wrote:
>> On 1/8/12 10:33 AM, Dave Whitla wrote:
>>>
>>>
>>> The issue persists in all kernels on the 2.6 branch. I've not
>>> experienced it with 3.x kernels but my scripts have disabled TX
>>> checksumming since I first came across the issue.
>>>
>>> The problem is that many people run VMs to support "legacy" systems
>>> on new high-capacity hardware or in production environments where we
>>> are compelled to run say RHEL which doesn't ship with a kernel newer
>>> than 2.6.35. So while this isn't an issue with OVS it probably should
>>> be prominently mentioned somewhere in your doco if only to avoid it
>>> appearing in list posts over and over.
>>>
>>> A fix belongs in Xen's netfront driver I think. I have assumed Hans
>>> is using Xen.
>>
>>
>> That's correct.
>>
>> I'm building a test setup for replacing numerous vlan-interfaces and bridges
>> on a Xen setup using ovs on Debian GNU/Linux stable, which has linux 2.6.32
>> and Xen 4.0.
> 
> In the setup that you've described, traffic isn't actually going
> through any of Xen's network interfaces, right?  i.e. it's originating
> on the OVS internal device rather than from a VM.
> 
> Assuming that's the case, I believe these two issues have different
> root causes with different solutions.

Ah, yes, sorry, that comment was posted a bit too quick. This particular
checksum offloading issue had nothing to do with the role of Xen
networking between host and vm's in the setup.

I suspect the hardware to be the 'root cause' (some old broadcom 5706
using tg3 driver in linux)... I have another very weird issue with this
testbox, which I'll try to report this week.

-- 
Hans van Kranenburg - System / Network Engineer
T +31 (0)10 2760434 | hans.van.kranenburg at mendix.com | www.mendix.com

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