Re: copyless virtio net thoughts?

[Rusty Russell <rusty@rustcorp.com.au>]

On Thursday 19 February 2009 10:01:42 Simon Horman wrote:
> On Wed, Feb 18, 2009 at 10:08:00PM +1030, Rusty Russell wrote:
> > 
> > 2) Direct NIC attachment This is particularly interesting with SR-IOV or
> > other multiqueue nics, but for boutique cases or benchmarks, could be for
> > normal NICs.  So far I have some very sketched-out patches: for the
> > attached nic dev_alloc_skb() gets an skb from the guest (which supplies
> > them via some kind of AIO interface), and a branch in netif_receive_skb()
> > which returned it to the guest.  This bypasses all firewalling in the
> > host though; we're basically having the guest process drive the NIC
> > directly.
> 
> Hi Rusty,
> 
> Can I clarify that the idea with utilising SR-IOV would be to assign
> virtual functions to guests? That is, something conceptually similar to
> PCI pass-through in Xen (although I'm not sure that anyone has virtual
> function pass-through working yet).

Not quite: I think PCI passthrough IMHO is the *wrong* way to do it: it makes migrate complicated (if not impossible), and requires emulation or the same NIC on the destination host.

This would be the *host* seeing the virtual functions as multiple NICs, then
the ability to attach a given NIC directly to a process.

This isn't guest-visible: the kvm process is configured to connect directly to a NIC, rather than (say) bridging through the host.

> If so, wouldn't this also be useful
> on machines that have multiple NICs?

Yes, but mainly as a benchmark hack AFAICT :)

Hope that clarifies,
Rusty.