Re: [Qemu-devel] >256 Virtio-net-pci hotplug Devices

[Kinsella, Ray]

Hi Marcel,

> You can use multi-function PCIe Root Ports, this will give you 8 ports
> per slot, if you have 16 empty slots (I think we have more) you reach
> 128 root ports.
> Then you can use multi-function  virtio-net-pci devices, this will
> give you 8 functions per port, so you reach the target of 1024 devices.
>
> You loose hot-plug granularity since you can hot-plug 8-functions group,
> but maybe is OK, depending on your scenario.

Thanks for the advice losing the hotplug granularity is something I 
think I can live with. It would mean, I would have to track how many 
ports are allocated to a VM, and create 8 new ports when 1 is required, 
caching the other 7 for when they are needed.

> Even so, you can use one cold-plugged pxb-pcie if you don't
> have enough empty slots on pcie.0, in order to reach the maximum
> number of PCIe Root Ports (256) which is the maximum for a single
> PCI domain.

Took your advice see the attached cfg, it works exactly as you 
indicated. If you are interested, you can use it from your VM adding 
-readconfig to your qemu cmd line. I can currently only manage to start 
a VM with around 50 coldplugged virtio devices before something breaks. 
Not sure what yet, I will try scaling it with hotplugging tomorrow.

> If you need granularity per single device (1000+ hot-pluggable),
> you could enhance the pxb-pcie to support multiple pci domains.

Do think there would be much work in this?

Thanks,

Ray K

test.cfg.gz
Description: application/gzip