Re: copyless virtio net thoughts?

[Arnd Bergmann <arnd@arndb.de>]

On Thursday 19 February 2009, Rusty Russell wrote:

> 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.

I guess what you mean then is what Intel calls VMDq, not SR-IOV.
Eddie has some slides about this at
http://docs.huihoo.com/kvm/kvmforum2008/kdf2008_7.pdf .

The latest network cards support both operation modes, and it
appears to me that there is a place for both. VMDq gives you
the best performance without limiting flexibility, while SR-IOV
performance in theory can be even better, but sacrificing a
lot of flexibility and potentially local (guest-to-gest)
performance.

AFAICT, any card that supports SR-IOV should also allow a VMDq
like model, as you describe.

	Arnd <><