On Thu, Nov 06, 2008 at 04:38:40PM -0600, Anthony Liguori wrote: > >It's not clear thats the right solution. If the VF devices are _only_ > >going to be used by the guest, then arguably, we don't want to create > >pci_devs for them in the host. (I think it _is_ the right answer, but I > >want to make it clear there's multiple opinions on this). > > The VFs shouldn't be limited to being used by the guest. > > SR-IOV is actually an incredibly painful thing. You need to have a VF > driver in the guest, do hardware pass through, have a PV driver stub in > the guest that's hypervisor specific (a VF is not usable on it's own), > have a device specific backend in the VMM, and if you want to do live > migration, have another PV driver in the guest that you can do teaming > with. Just a mess. Not to mention that you basically have to statically allocate them up front. > What we would rather do in KVM, is have the VFs appear in the host as > standard network devices. We would then like to back our existing PV > driver to this VF directly bypassing the host networking stack. A key > feature here is being able to fill the VF's receive queue with guest > memory instead of host kernel memory so that you can get zero-copy > receive traffic. This will perform just as well as doing passthrough > (at least) and avoid all that ugliness of dealing with SR-IOV in the guest. This argues for ignoring the SR-IOV mess completely. Just have the host driver expose multiple 'ethN' devices. > This eliminates all of the mess of various drivers in the guest and all > the associated baggage of doing hardware passthrough. > > So IMHO, having VFs be usable in the host is absolutely critical because > I think it's the only reasonable usage model. > > Regards, > > Anthony Liguori > -- > To unsubscribe from this list: send the line "unsubscribe linux-pci" in > the body of a message to majordomo@xxxxxxxxxxxxxxx > More majordomo info at http://vger.kernel.org/majordomo-info.html -- Matthew Wilcox Intel Open Source Technology Centre "Bill, look, we understand that you're interested in selling us this operating system, but compare it to ours. We can't possibly take such a retrograde step." -- To unsubscribe from this list: send the line "unsubscribe linux-pci" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
