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

[Ian Campbell <ian.campbell@xxxxxxxxxx>]

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.
> Thanks.
> -Nate
> ---------------------------------------------------------
> 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
> exited
> 
> 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 4.1.6.1 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.

Ian.


_______________________________________________
Xen-users mailing list
Xen-users@xxxxxxxxxxxxx
http://lists.xen.org/xen-users