Re: [virtio-comment] [PATCH v10 00/10] Introduce device group and device management

[Jiri Pirko <jiri@nvidia.com>]

Mon, Mar 06, 2023 at 11:54:45PM CET, mst@redhat.com wrote:
>On Mon, Mar 06, 2023 at 01:29:30PM +0100, Jiri Pirko wrote:
>> Thu, Mar 02, 2023 at 02:04:48PM CET, mst@redhat.com wrote:
>> 
>> [...]
>> 
>> >
>> >TODO (maybe?) - probably ok to defer until this part is upstream:
>> >
>> >	Add "all members" member id.
>> >
>> >	Add commands for MSI, feature discovery.
>> >
>> >	Add commands for transport vq.
>> >
>> >
>> >My intent is to try and support both SR-IOV and SIOV
>> >usecases with the same structure and maybe even the same
>> >VQ.
>> 
>> Sorry to be late to the party, I'm trying to catch up. Is it common to
>> have cover letter for features this brief? I mean, from the cover
>> letter, I'm totally unable to understand what you are introducing here.
>> 
>> Could you elaborate about what you are aiming to achive with this?
>> Could you shed some usecases perhaps?
>> 
>> I have to be missing something obvious, but I don't get why any notion
>> of SR-IOV could be beneficial for virtio.
>> 
>
>Good point, I'll add a bit of motivation.
>
>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 :/


>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 :)


>
>
>
>
>> >
>> >For example, it might make sense to split creating/destroying
>> >SIOV devices from the transport passing data from the guest - the
>> >driver would then not negotiate VIRTIO_F_SR_IOV (which
>> >then means auto-provisioning).
>> >
>> >This is out of RFC, since we have two commands which are useful
>> >to discover supported group types (ATM can be none or SR-IOV).
>> >
>> >
>> >Michael S. Tsirkin (10):
>> >  virtio: document forward compatibility guarantees
>> >  admin: introduce device group and related concepts
>> >  admin: introduce group administration commands
>> >  admin: introduce virtio admin virtqueues
>> >  pci: add admin vq registers to virtio over pci
>> >  mmio: document ADMIN_VQ as reserved
>> >  ccw: document ADMIN_VQ as reserved
>> >  admin: command list discovery
>> >  admin: conformance clauses
>> >  ccw: document more reserved features
>> >
>> > admin.tex        | 540 +++++++++++++++++++++++++++++++++++++++++++++++
>> > content.tex      | 112 +++++++++-
>> > introduction.tex |   3 +
>> > 3 files changed, 653 insertions(+), 2 deletions(-)
>> > create mode 100644 admin.tex
>> >
>> >-- 
>> >MST
>> >
>> >
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>> >
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