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

From: "Michael S. Tsirkin" <[email-masked]>
Date: Sun, 21 Mar 2010 11:55:44 +0200

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.

-- 
MST