virtio — archive

[Lingshan Zhu <mst@redhat.com>]

On 3/8/2023 3:31 AM, Parav Pandit wrote: >> From: Michael S. Tsirkin <mst@redhat.com> >> Sent: Tuesday, March 7, 2023 12:20 PM > [..] >>>> For SR-IOV, it is not unusual for PFs to excercise control over VFs. >>> I understand the concepts of SR-IOV. Yet I fail to see the need of >>> such concept in virtio world. SR-IOV is very specific solution for PCI >>> functions instantiation, and I believe that it is already considered >>> quite limiting in many aspects. Does not make sense to me to introduce >>> it for virtio. But again, I may be missing something crucial, I just >>> would like to see the motivation, needs, usecases for this crystal >>> clear, which is opposite to the current cover letter I'm afraid :/ >> First people are asking for it because it's out there, however limiting it is. In >> fact Nvidia is - why don't you talk to Parav here and tell him that SR-IOV is >> legacy and there's no need to support. >> > Jiri and I discussed offline today. > SR-IOV is widely used today and in the coming future up to thousands of devices. > Many vendors are building it or already built. > > SIOV as it stands today is still being crafted at various levels iommu, os, device, pci and more. > Not there yet fully. > > Jiri and I built the Linux kernel interfaces for SFs which are equivalent to SIOVs that overcome some of the SR-IOV limitations. > And Jiri's suggestion was to leverage some of the vision and practice from there. > > In other words, can AQ command be useful tomorrow for doing SIOV device add/remove, and provisioning from non-owning PF? > The way AQ is crafted today is not there yet, but in the future, it can be extended. I have submitted a series implementing "transport vq" which work for ADIs like SIOV devices, MST required a merge with admin q, so we are here. >>>> There is interest in the community to include an interface to allow >>>> this in the virtio spec, when the PF is a virtio device. This is >>>> what this patch does. >>> Yeah, but why? As I asked before, what are the usecases? The fact >>> there is interest in the community does not mean it makes sense to >>> have it :) >>> >> If people want to build such hardware it will need some interface. >> Far better to have it standard. >> >> >> But generally e.g. intel already said they will reuse this same structure with a >> different group type for SIOV support. >> I'll mention this in the cover letter. >> > We have the following already identified use cases of a device agnostic VQ. > > 1. SR-IOV VF device provisioning at virtio layer (features and config) > 2. SR IOV (SR-PCIM interface of the PCI spec) for VF provisioning, for example, MSI-X vectors > > 3. SR-IOV VF Live migration > 4. Above #1 to #3 for SIOV devices instead of SRIOV devices > > 5. cmd q interface for PF/VF/SF/SIOV to transport their own features, config command over queue interface without any parent device > > #1 to #3 are well described in past. So, It is worth covering them in the cover letter and things will be clear for new eyes. > #4 is broad use case and like #1 to #3 that will eventually happen. > #5 likely needs more discussion, we can differ to a later point because AQ needs to progress in spec 1.3. > >