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Date: Thu, 14 Oct 2010 14:07:17 +0200
From: Avi Kivity <avi@redhat.com>
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Subject: Re: [Qemu-devel] Hitting 29 NIC limit
References: <C8DB8174.2FEBC%anjali@juniper.net> <4CB6388A.30006@codemonkey.ws>
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To: Anthony Liguori <anthony@codemonkey.ws>
Cc: Anjali Kulkarni <anjali@juniper.net>, "qemu-devel@nongnu.org" <qemu-devel@nongnu.org>, "kvm@vger.kernel.org" <kvm@vger.kernel.org>

  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.

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

-- 
error compiling committee.c: too many arguments to function