On 3/8/2023 3:31 AM, Parav Pandit wrote:
>>
From: Michael S. Tsirkin <>
>> 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.
>
>
