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Re: [Xen-users] Error with 5+ network interfaces

  • To: xen-users@xxxxxxxxxxxxx
  • From: Nate Soule <nsoule@xxxxxxx>
  • Date: Fri, 08 May 2015 13:12:31 -0400
  • Delivery-date: Fri, 08 May 2015 17:13:47 +0000
  • List-id: Xen user discussion <xen-users.lists.xen.org>

Thanks very much for the background and your help Ian. Moving to PV NICs may well be fine in our situation. I have not yet tested that, but adding device_model_version="qemu-xen-traditional" to my configuration did the trick as well.

Thanks again, this was a huge help!


On 05/08/2015 05:34 AM, Ian Campbell wrote:
On Thu, 2015-05-07 at 15:11 -0400, Nate Soule wrote:
I posted this question on the Xen general form, but got the advice
that this was a complex enough issue that this mailing list may be the
better venue. Any advice would be greatly appreciated. See original
posting below.
Hi, I'm attempting to create/start a guest VM with 5 network
interfaces (all bridges, specified in vif= line in config file, see
below). With 1, 2, 3, and 4 interfaces defined the VM starts perfectly
fine. With 5 or more interfaces defined I get the following errors
upon executing "sudo xl create SWITCH.cfg"

Parsing config from SWITCH.cfg
libxl: error: libxl_dm.c:1388:device_model_spawn_outcome: domain 16
device model: spawn failed (rc=-3)
libxl: error: libxl_create.c:1186:domcreate_devmodel_started: device
model did not start: -3
libxl: error: libxl_dm.c:1492:kill_device_model: Device Model already

and the VM does not start.

Is there any known limitation on number of network interfaces?

Both dom0 and the domU are Ubuntu 14.04 (server edition). I have
replicated this on two separate physical machines (one with 8 GB RAM,
the other with 32 GB, in case it's relevant). I'm using Xen 4.4.1.
I believe this bug was fixed in Xen 4.5. It's to do with the amount of
memory used by the option roms for each emulated NIC, if you have too
many it exhausts the slack space set aside for such things.

If you have PV drivers in the guest then you could try specifying
type=vif for one or more of the devices to force them to PV only mode
such that you only have <=4 emulated NICs. Using PV is good practice
anyway since it will perform much better.

If you really need emulated NICs for some reason then I'm not sure if
there is a workaround in 4.4 but you could try seeing if there is some
backdoor way to disable that (perhaps using the device_model_args option
in the cfg file to pass extra stuff to qemu).

I tried on a 3rd machine running Xen and I do not appear to
get the issue there.
4.1 used an older qemu by default which didn't suffer from this sort of
thing, it's only the upstream version of qemu which has it (due to
changes in the way modern qemu accounts for memory etc).

Which suggests that device_model_version="qemu-xen-traditional" in your
config might also suffice as a workaround on 4.4.


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