Re: [PATCH RFC v4 0/7] virtio-net: add support for SR-IOV emulation

[Yui Washizu]

On 2024/07/15 14:15, Akihiko Odaki wrote:
> On 2024/05/16 11:00, Yui Washizu wrote:
> > On 2024/04/28 18:05, Akihiko Odaki wrote:
> > > Based-on: <20240315-reuse-v9-0-67aa69af4d53@daynix.com>
> > > ("[PATCH for 9.1 v9 00/11] hw/pci: SR-IOV related fixes and 
> > > improvements")
> > >
> > > Introduction
> > > ------------
> > >
> > > This series is based on the RFC series submitted by Yui Washizu[1].
> > > See also [2] for the context.
> > >
> > > This series enables SR-IOV emulation for virtio-net. It is useful
> > > to test SR-IOV support on the guest, or to expose several vDPA devices
> > > in a VM. vDPA devices can also provide L2 switching feature for
> > > offloading though it is out of scope to allow the guest to configure
> > > such a feature.
> > >
> > > The PF side code resides in virtio-pci. The VF side code resides in
> > > the PCI common infrastructure, but it is restricted to work only for
> > > virtio-net-pci because of lack of validation.
> > >
> > > User Interface
> > > --------------
> > >
> > > A user can configure a SR-IOV capable virtio-net device by adding
> > > virtio-net-pci functions to a bus. Below is a command line example:
> > >    -netdev user,id=n -netdev user,id=o
> > >    -netdev user,id=p -netdev user,id=q
> > >    -device pcie-root-port,id=b
> > >    -device virtio-net-pci,bus=b,addr=0x0.0x3,netdev=q,sriov-pf=f
> > >    -device virtio-net-pci,bus=b,addr=0x0.0x2,netdev=p,sriov-pf=f
> > >    -device virtio-net-pci,bus=b,addr=0x0.0x1,netdev=o,sriov-pf=f
> > >    -device virtio-net-pci,bus=b,addr=0x0.0x0,netdev=n,id=f
> > >
> > > The VFs specify the paired PF with "sriov-pf" property. The PF must be
> > > added after all VFs. It is user's responsibility to ensure that VFs 
> > > have
> > > function numbers larger than one of the PF, and the function numbers
> > > have a consistent stride.
> >
> >
> > I tried to start a VM with more than 8 VFs allocated using your patch,
> > but the following error occured and qemu didn't work:
> > VF function number overflows.
> >
> > I think the cause of this error is that virtio-net-pci PFs don't have 
> > ARI.
> > (pcie_ari_init is not added to virtio-net-pci when PFs are initialized.)
> > I think it is possible to add it later,
> > but how about adding pcie_ari_init ?
> >
> > As a trial,
> > adding pcie_ari_init to virtio_pci_realize enabled the creation of 
> > more than 8 VFs.
>
> I have just looked into that possibility, but adding pcie_ari_init to 
> virtio_pci_realize has some implications. Unconditionally calling 
> pcie_ari_init will break the existing configuration of virtio-pci 
> devices so we need to implement some logic to detect when ARI is 
> needed. Preferably such logic should be implemented in the common PCI 
> infrastructure instead of implementing it in virtio-pci so that other 
> PCI multifunction devices can benefit from it.
>
> While I don't think implementing this will be too complicated, I need 
> to ensure that such a feature is really needed before doing so.


OK.
I want to use this emulation for offloading virtual network
in a environment where there are many containers in VMs.
So, I consider that the feature is need.
I think that 7 VFs are too few.
I'll keep thinking about the feature's necessity.


I'll add other comments to RFC v5 patch.


Regards,

Yui Washizu