On 24 April 2015 at 11:47, Stefan Hajnoczi <[email protected]> wrote:
> My concern is the overhead of the vhost_net component copying
> descriptors between NICs.
I see. So you would not have to reserve CPU resources for vswitches.
Instead you would give all cores to the VMs and they would pay for their
own networking. This would be especially appealing in the extreme case
where all networking is "Layer 1" connectivity between local virtual
machines.
This would make VM<->VM links different to VM<->network links. I suppose
that when you created VMs you would need to be conscious of whether or not
you are placing them on the same host or NUMA node so that you can predict
what network performance will be available.
For what it is worth, I think this would make life more difficult for
network operators hosting DPDK-style network applications ("NFV").
Virtio-net would become a more complex abstraction, the orchestration
systems would need to take this into account, and there would be more
opportunity for interoperability problems between virtual machines.
The simpler alternative that I prefer is to provide network operators with
a Virtio-net abstraction that behaves and performs in exactly the same way
for all kinds of network traffic -- whether or not the VMs are on the same
machine and NUMA node.
That would be more in line with SR-IOV behavior which seems to me like the
other horse in this race. Perhaps my world view here is too narrow though
and other technologies like ivshmem are more relevant than I give them
credit for?
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