Re: [Qemu-devel] Intermittent e1000 failure on qemu-kvm 1.0

[Chris Webb]

Hi. Sorry for the slow follow-up.

Stefan Hajnoczi <address@hidden> writes:

> Yes, it's odd that QEMU changes make the issue go away but tcpdump
> suggests the packet is not being sent from the bridge to the tap
> device.

Indeed. I really don't understand how to the two could possible interact!

> e1000 and rtl8139 both use the same QEMU network subsystem code.  I
> don't see an obvious difference between the two.

I wondered whether it could be some sort of checksum offloading which
doesn't apply for virtio or rtl8139, but otherwise I agree it's extremely
strange.

> Since this issue only happens once in many QEMU runs are you sure that
> -usbdevice tablet really makes the issue go away?

I ran in a tight loop without it for around 500 iterations, and have done so
again to confirm. Typically it fails within 20-40 iterations with -usbdevice
tablet present.

> Are you using ebtables?  I know you mentioned disabling iptables and
> it would be good to try the same for ebtables if you use it.

We're normally using ebtables, but I completely flushed all the tables and
set policy of ACCEPT for these tests to eliminate the possibility of bugs in
my table create code.

> In order to debug the host networking issue you may be able to use
> ebtables/iptables LOG targets to collect information on how far
> exactly the packets are getting.  For example, you could try logging
> all packets destined for the guest MAC address - and if the log
> information includes the network interface you should see the packet
> move between its source, the bridge, and the destination interface.  I
> have never tried this but it might work.

I will have a play with this.

Cheers,

Chris.