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

From: Avi Kivity <[email-masked]>
Date: Sun, 21 Mar 2010 12:11:33 +0200

On 03/21/2010 11:55 AM, Michael S. Tsirkin wrote:
> 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.
>    

Increase it to 200, then.

Is the limit visible to userspace?  If not, we need to expose it.

-- 
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