Re: Unable to create more than 1 guest virtio-net device using vhost-net backend

Michael S. Tsirkin
2010-03-21T09:55:44Z

On Fri, Mar 19, 2010 at 03:19:27PM -0700, Sridhar Samudrala wrote:
> When creating a guest with 2 virtio-net interfaces, i am running
> into a issue causing the 2nd i/f falling back to userpace virtio
> even when vhost is enabled.
>
> After some debugging, it turned out that KVM_IOEVENTFD ioctl()
> call in qemu is failing with ENOSPC.
> This is because of the NR_IOBUS_DEVS(6) limit in kvm_io_bus_register_dev()
> routine in the host kernel.
>
> I think we need to increase this limit if we want to support multiple
> network interfaces using vhost-net.
> Is there an alternate solution?
>
> Thanks
> Sridhar

Nothing easy that I can see. Each device needs 2 of these. Avi, Gleb,
any objections to increasing the limit to say 16? That would give us
5 more devices to the limit of 6 per guest.

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MST