Re: Hitting 29 NIC limit

["Michael S. Tsirkin" <mst@redhat.com>]

On Thu, Oct 14, 2010 at 02:07:17PM +0200, Avi Kivity wrote:
>  On 10/14/2010 12:54 AM, Anthony Liguori wrote:
> >On 10/13/2010 05:32 PM, Anjali Kulkarni wrote:
> >>
> >>Hi,
> >>
> >>Using the legacy way of starting up NICs, I am hitting a
> >>limitation after 29
> >>NICs ie no more than 29 are detected (that's because of the 32 PCI slot
> >>limit on a single bus- 3 are already taken up)
> >>I had initially increased the MAX_NICS to 48, just on my tree, to get to
> >>more, but ofcource that wont work.
> >>Is there any way to go beyond 29 NICs the legacy way?  What is
> >>the maximum
> >>that can be supported by the qdev mothod?
> >
> >I got up to 104 without trying very hard using the following script:
> >
> >args=""
> >for slot in 5 6 7 8 9 10 11 12 13 14 15 16 17; do
> >for fn in 0 1 2 3 4 5 6 7; do
> >    args="$args -netdev user,id=eth${slot}_${fn}"
> >    args="$args -device virtio-net-pci,addr=${slot}.${fn},netdev=eth${slot}_${fn},multifunction=on,romfile="
> >done
> >done
> >
> >x86_64-softmmu/qemu-system-x86_64 -hda ~/images/linux.img ${args}
> >-enable-kvm
> >
> >The key is to make the virtio-net devices multifunction and to
> >fill out all 8 functions for each slot.
> 
> This is unlikely to work right wrt pci hotplug.  If we want to
> support a large number of interfaces, we need true multiport cards.

Bridge support seems to be working mostly fine here.
That will let you go up to 256 devices without multifunction.

-- 
MST