Re: [Xen-users] Heavy Dom0 traffic stops network

[Simon Hobson <linux@xxxxxxxxxxxxxxxx>]

Fajar A. Nugraha wrote:

> On Mon, Feb 1, 2010 at 6:37 PM, Simon Hobson <linux@xxxxxxxxxxxxxxxx> wrote:
> >  However, it's not just traffic from Dom0 to DomU that does it. I've got a
> >  big transfer going from another machine copying large amounts of data to the
> >  same DomU - and ping is showing occasional dropped packets.
> >
> >
> >  So, anyone got hints on what;s causing it, and more importantly, how to fix
> >  it ?
> Do you have traffic limit somewhere? It sounds like the switch your
> physical machine connected to has port storm-control or similar. I'd
> suggest testing using crossover cable from server <-> laptop and use
> iperf (or other packet generators) to isolate the problem.
It's definitely not that - when not transferring data between Dom0 
and DomU on the same machine, I can shovel data around between DomUs 
and external partners with no problem.
The problem ONLY happens when Dom0 is exchanging data with a DomU it 
hosts. It's completely repeatable - start large transfer and wait, 
when the traffic stops I can hit ctrl-C and the network comes back to 
life.
So passing network traffic about is fine as long as Dom0 isn't 
involved at anything (other than a low rate) with one of it's own 
DomUs - I had to limit my rsync transfer to 25kbyte/s and even then 
it could cause a problem if there was other traffic going on.
Given bits I've picked up before, I'm guessing that there's a problem 
in the network handling process - one thread handling all traffic ? 
Wild stab in the dark, but it does sound a bit like some sort of 
mutual blocking going on - and stopping one partner then frees the 
other one up.
Is this something I should report as a bug ? What's the right way to 
do that ? Unfortunately, I don't have another non-production machine 
available at the moment so it's a bit difficult trying the later 
version from Debian Squeeze. I'll have a rummage around tomorrow, but 
I don't think anything has enough RAM.
--
Simon Hobson

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Alternatively, if anyone has one of these and would let me image 
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