[Openstack] [openstack-dev] Neutron support for passthrough of networking devices?

Chris Friesen chris.friesen at windriver.com
Thu Oct 10 14:50:43 UTC 2013

On 10/10/2013 01:19 AM, Prashant Upadhyaya wrote:
> Hi Chris,
> I note two of your comments --

>>> When we worked on H release, we target for basic PCI support
>>> like accelerator card or encryption card etc.

> PU> So I note that you are already solving the PCI pass through
> usecase somehow ? How ? If you have solved this already in terms of
> architecture then SRIOV should not be difficult.

Notice the double indent...that was actually Jiang's statement that I

>> Do we run into the same complexity if we have spare physical NICs
>> on the host that get passed in to the guest?

> PU> In part you are correct. However there is one additional thing.
> When we have multiple physical NIC's, the Compute Node's linux is
> still in control over those.


> In case of SRIOV, you can dice up a single
> physical NIC into multiple NIC's (effectively), and expose each of
> these diced up NIC's to a VM each. This means that the VM will now
> 'directly' access the NIC bypassing the Hypervisor.


> But if there are two
> physical NIC's which were diced up with SRIOV, then VM's on the diced
> parts of the first  physical NIC cannot communicate easily with the
> VM's on the diced parts of the second physical NIC. So a native
> implementation has to be there on the Compute Node which will aid
> this (this native implementation will take over the Physical
> Function, PF of each NIC) and will be able to 'switch' the packets
> between VM's of different physical diced up NIC's [if we need that
> usecase]

Is this strictly necessary?  It seems like it would be simpler to let 
the packets be sent out over the wire and the switch/router would send 
them back to the other NIC.  Of course this would result in higher use 
of the physical link, but on the other hand it would mean less work for 
the CPU on the compute node.


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