Re: [virtio-comment] [PATCH 5/5] virtio-pci: implement VIRTIO_F_QUEUE_STATE

["Zhu, Lingshan" <lingshan.zhu@intel.com>]

On 9/12/2023 5:06 PM, Zhu, Lingshan wrote:
> On 9/12/2023 3:53 PM, Parav Pandit wrote:
> > > From: Zhu, Lingshan <lingshan.zhu@intel.com>
> > > Sent: Tuesday, September 12, 2023 12:59 PM
> > >
> > > On 9/12/2023 2:49 PM, Parav Pandit wrote:
> > > > > From: Zhu, Lingshan <lingshan.zhu@intel.com>
> > > > > Sent: Tuesday, September 12, 2023 12:08 PM
> > > > >
> > > > > On 9/12/2023 1:51 PM, Parav Pandit wrote:
> > > > > > > From: Zhu, Lingshan <lingshan.zhu@intel.com>
> > > > > > > Sent: Tuesday, September 12, 2023 9:19 AM
> > > > > > >
> > > > > > > On 9/11/2023 7:50 PM, Parav Pandit wrote:
> > > > > > > > > From: Zhu, Lingshan <lingshan.zhu@intel.com>
> > > > > > > > > Sent: Monday, September 11, 2023 3:03 PM By the way, do you see
> > > > > > > > > anything we need to improve in this series?
> > > > > > > > Admin commands for passthrough devices of [1] is comprehensive
> > > > > > > > proposal
> > > > > > > covering all the aspects.
> > > > > > > > To me [1] is superset work that covers all needed functionality
> > > > > > > > and downtime
> > > > > > > aspects.
> > > > > > > > I plan to improve [1] with v1 this week by extending device
> > > > > > > > context and
> > > > > > > addressing other review comments.
> > > > > > > > [1]
> > > > > > > > https://lists.oasis-open.org/archives/virtio-comment/202309/msg000
> > > > > > > > 61
> > > > > > > > .h
> > > > > > > > tml
> > > > > > > I am not sure, we have discussed a lot about the potential issues
> > > > > > > in the treads. I guess we should resolve them first. E.g., 
> > > > > > > nested use cases.
> > > > > > You are using nesting use case as the _only_ use case and attempt to
> > > > > > steer
> > > > > using that.
> > > > > > Not right.
> > > > > >
> > > > > > If you want to discuss, then lets have both the use cases, attempt
> > > > > > to converge
> > > > > and if we can its really good.
> > > > > > If we cannot, both requirements should be handled differently.
> > > > > Isn't nested a clear use case that should be supported?
> > > > Most users who care for running real applications and real 
> > > > performance, have
> > > not asked for nesting.
> > > > It is not mandatory case; it may be required for some users.
> > > > I donât know who needs M level nesting and how cpu also support its
> > > acceleration etc to run some reasonable workload.
> > > Nested is a common use case and it is mandatory.
> > Maybe it is common case for the users you interact with, it is 
> > required for some complicated mode.
> > How many level of nesting 10, 2, 100?
> >
> > I donât see a point of debating that "nesting is the only case and 
> > mediation is the only way" to do device migration.
> >
> > As I repeatedly acknowledged,
> > We are open to converge on doing administration commands that can 
> > work for passthrough and nested way.
> >
> > I just donât see how nested solution can work without any mediation, 
> > as everything you do touches device reset and FLR flow and it 
> > practically breaks the PCI specification with these side band 
> > registers and faking device reset and FLR when asked.
> > This is the primary reason; I am less inclined to go the in-band method.
> > Until now, no one technically explained how it can even work on 
> > question from yesterday.
> >
> > And if there is one, please explain, I am very interested to learn, 
> > how is this done without hacks where device reset by guest _actually_ 
> > reset the underlying member device while the dirty page tracking is 
> > also ongoing.
> >
> > So, my humble request is, try to work towards co-existing both the 
> > methods if possible, rather than doing either or mode.
> If you want AQ used for LM, it should support nested anyway, don't 
> break user logic.
>
>
> This (my)series can support nested.
supplementary: As Jason ever pointed out: the two solution can co-exist 
for sure, I am implementing basic facilities, admin vq can free feel to 
reuse them like forwarding messages to them, and this can help support 
nested.