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

[Simon Hobson <linux@xxxxxxxxxxxxxxxx>]

On 11/10/09, I wrote:
> I've just experienced a rather strange one ...
>
> I was trying to create a new DomU using debootstrap as I've done 
> before - and everything stopped, quickly followed by a voice from 
> downstairs asking why the internet had stopped ! This first happened 
> yesterday, and assuming I'd perhaps managed some form of resource 
> exhaustion I rebooted the system.
> Today I tried again (but without the "when will it be working ?" 
> from downstairs) and found this.
> If I do a ping from my laptop to a DomU, then the responses just 
> stop a short while after I hit the network from Dom0 (it only takes 
> a few MB). If I stop the traffic and wait, then it all comes back 
> again after about 5 minutes :
> 64 bytes from 192.168.0.34: icmp_seq=465 ttl=64 time=0.290 ms
> 64 bytes from 192.168.0.34: icmp_seq=466 ttl=64 time=0.292 ms
> 64 bytes from 192.168.0.34: icmp_seq=467 ttl=64 time=0.338 ms
> 64 bytes from 192.168.0.34: icmp_seq=468 ttl=64 time=297024.510 ms
> 64 bytes from 192.168.0.34: icmp_seq=469 ttl=64 time=296024.293 ms
> 64 bytes from 192.168.0.34: icmp_seq=470 ttl=64 time=295024.138 ms
> Note that packets don't seem to have been lost, just queued up.
>
> "brctl showmacs eth0" shows MAC addresses aging in the bridge.
>
> Dom0 has one bridge on the inside network, internet access is via a 
> router running in a DomU with external ethernet interface made 
> available to it via pciback.
> Dom0 is Debian Etch, linux-image-2.6.18-6-xen-amd64  2.6.18.dfsg.1-23etch1
> running on xen-hypervisor-3.2-1-amd64  3.2.1-2~bpo4+1
>
> The guests are running Lenny.
>
> Nothing appears to be logged when the problem happens. Any ideas ?

I've now hit this one at work. In this case, it's a four core Xeon - 
and I've tried pinning Dom-0 to core 0, and the guests to cores 1-3. 
I've further found that if I kill the transfer then networking 
returns instantly. So I can run a network intensive transfer (rsync) 
while watching the pings - the pings stop, I hit ctrl-c, the pings 
recover with no dropped packets.
Dom-0 is running Debian Lenny linux-image-2.6.18-6-xen-686 
(2.6.18.dfsg.1-22) and xen-hypervisor-3.2-1-i386 (3.2.1-2)
Dom-U is running Lenny and the same kernel. It's also storing the 
data on an iSCSI volume (iSCSI handled by Dom0 and exported to DomU).
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 ?
--
Simon Hobson

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printer OS on it. If anyone knows where I might get hold of one I'd 
be grateful - requests to Canon drew a blank, it's been out of 
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Alternatively, if anyone has one of these and would let me image 
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Visit http://www.magpiesnestpublishing.co.uk/ for books by acclaimed
author Gladys Hobson. Novels - poetry - short stories - ideal as
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