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Re: [Qemu-devel] Hitting 29 NIC limit


From: Anthony Liguori
Subject: Re: [Qemu-devel] Hitting 29 NIC limit
Date: Thu, 14 Oct 2010 07:54:22 -0500
User-agent: Mozilla/5.0 (X11; U; Linux x86_64; en-US; rv:1.9.1.12) Gecko/20100915 Lightning/1.0b1 Thunderbird/3.0.8

On 10/14/2010 07:07 AM, 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.

Yes. Our hotplug design is based on devices.. This is wrong, it should be based on bus-level concepts (like PCI slots).

If we want to support a large number of interfaces, we need true multiport cards.

This magic here creates a multiport virtio-net card so I'm not really sure what you're suggesting. It would certainly be nice to make this all more user friendly (and make hotplug work).

Regards,

Anthony Liguori

What's the motivation for such a huge number of interfaces?




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