Re: [PATCH 0/4] Support accelerated network plugin modules

[Jambunathan K <jambunathan@netxen.com>]

Kieran


>> I have a question regarding the feature set that is proposed here. The
>> intention is to further my own understanding and get some additional
>> insights.
>>
>> Doesn't accelerated network plugins solve the same problem as say a
>> "native" PCI passthroughed driver. Put other way, what can an
>> accelerator do that a passthroughed driver cannot do?
> 
> Functionally they're similar, in that they both enable a guest to get
> direct access to the NIC to deliver higher network performance, but off
> the top of my head:
> 
>  - PCI passthrough would require hardware to support multiple PCI
> devices.  The accelerated plugin approach we've put forward doesn't (but
> would also work fine with devices that virtualise at the PCI layer), and
> so would support a wider range of devices.
> 
>  - You're limited with PCI passthrough to the number of PCI devices your
> NIC can support, which is (for the NICs I've seen) considerably less
> than the number of VIs that other NICs can support.  This will limit the
> number of guests you can provide accelerated network interfaces to.
> 
>  - I'm not sure what the story is for migration with PCI passthrough,
> but with the accelerated plugin approach your network interfaces can
> transparently (as far as the guest's network stack is concerned) move
> from being accelerated to not-accelerated (and vice-versa) depending on
> what hardware is available, and migrate from one type of accelerated
> hardware to another.  
> 
>  - A PCI-passthrough-based network interface might struggle to route
> packets to a virtual machine on the same host.  The accelerated network
> plugin can just fall back to the netfront/netback normal network path to
> get packets to these, or use facilities on the NIC to achieve the same
> if available.
> 
> In summary, it's "passthrough" rather than "PCI passthrough", if that
> makes sense.
> 

My understanding very much tallies with the points you have outlined above.

The patches you have submitted is of interest to us. It is possible that
in the near future we would get around to integrating and exercising
your changes against our own driver.

Jambunathan K.