Re: PCI pass-through of NIC to PV DomU... worth it?

["Cherry G. Mathew" <cherry.g.mathew%gmail.com@localhost>]

Hi David,

On 24 February 2012 09:21, David Howland <metalliqaz%fastmail.fm@localhost> 
wrote:
> Either my Google-fu is weak or nobody has actually asked this in the open
> before...
>
> Is it worth it to try and use PCI pass-through to give a NIC to a PV DomU?
>  I'm setting up a DomU firewall/router.  I want the latency to be as low as
> possible.
>
> I need to know which is faster: the PV network interface or passing the NIC?

That would depend on your card - if it's got "hardware acceleration"
(TSO, et. al) it could free up the main cpu. Also note that a single
backend driver handles *all* your domU traffic, so this is a potential
bottleneck (I have no idea if it is in practice).

Why not try both and find out ?

>  I don't have VT-d support, but the server is a dual quad-core Xeon setup,
> so I shouldn't be short on compute cycles.  My gut is telling me that there
> wouldn't be any tangible difference, but I want to hear what the experts
> think.

I'm not an expert, and I haven't tried it, but I think PCI passthrough
on xen requires VT-d (for partitioning/security rather than
efficiency).

-- 
~Cherry