RE: [virtio-comment] Re: [PATCH V2 4/6] virtio-pci: implement VIRTIO_F_QUEUE_STATE

[Parav Pandit <parav@nvidia.com>]

> From: Zhu, Lingshan <lingshan.zhu@intel.com>
> Sent: Friday, November 17, 2023 3:32 PM
> To: Parav Pandit <parav@nvidia.com>; jasowang@redhat.com;
> mst@redhat.com; eperezma@redhat.com; cohuck@redhat.com;
> stefanha@redhat.com
> Cc: virtio-comment@lists.oasis-open.org
> Subject: Re: [virtio-comment] Re: [PATCH V2 4/6] virtio-pci: implement
> VIRTIO_F_QUEUE_STATE
> 
> 
> 
> On 11/16/2023 6:21 PM, Parav Pandit wrote:
> >> From: Zhu, Lingshan <lingshan.zhu@intel.com>
> >> Sent: Thursday, November 16, 2023 3:45 PM
> >>
> >> On 11/16/2023 1:35 AM, Parav Pandit wrote:
> >>>> From: Zhu, Lingshan <lingshan.zhu@intel.com>
> >>>> Sent: Monday, November 13, 2023 2:56 PM
> >>>>
> >>>>
> >>>>
> >>>> On 11/10/2023 8:31 PM, Parav Pandit wrote:
> >>>>>> From: Zhu, Lingshan <lingshan.zhu@intel.com>
> >>>>>> Sent: Friday, November 10, 2023 1:22 PM
> >>>>>>
> >>>>>>
> >>>>>> On 11/9/2023 6:25 PM, Parav Pandit wrote:
> >>>>>>>> From: Zhu, Lingshan <lingshan.zhu@intel.com>
> >>>>>>>> Sent: Thursday, November 9, 2023 3:39 PM
> >>>>>>>>
> >>>>>>>>
> >>>>>>>> On 11/9/2023 2:28 PM, Parav Pandit wrote:
> >>>>>>>>>> From: Zhu, Lingshan <lingshan.zhu@intel.com>
> >>>>>>>>>> Sent: Tuesday, November 7, 2023 3:02 PM
> >>>>>>>>>>
> >>>>>>>>>> On 11/6/2023 6:52 PM, Parav Pandit wrote:
> >>>>>>>>>>>> From: Zhu, Lingshan <lingshan.zhu@intel.com>
> >>>>>>>>>>>> Sent: Monday, November 6, 2023 2:57 PM
> >>>>>>>>>>>>
> >>>>>>>>>>>> On 11/6/2023 12:12 PM, Parav Pandit wrote:
> >>>>>>>>>>>>>> From: Zhu, Lingshan <lingshan.zhu@intel.com>
> >>>>>>>>>>>>>> Sent: Monday, November 6, 2023 9:01 AM
> >>>>>>>>>>>>>>
> >>>>>>>>>>>>>> On 11/3/2023 11:50 PM, Parav Pandit wrote:
> >>>>>>>>>>>>>>>> From: virtio-comment@lists.oasis-open.org
> >>>>>>>>>>>>>>>> <virtio-comment@lists.oasis- open.org> On Behalf Of
> >>>>>>>>>>>>>>>> Zhu, Lingshan
> >>>>>>>>>>>>>>>> Sent: Friday, November 3, 2023 8:27 PM
> >>>>>>>>>>>>>>>>
> >>>>>>>>>>>>>>>> On 11/3/2023 7:35 PM, Parav Pandit wrote:
> >>>>>>>>>>>>>>>>>> From: Zhu Lingshan <lingshan.zhu@intel.com>
> >>>>>>>>>>>>>>>>>> Sent: Friday, November 3, 2023 4:05 PM
> >>>>>>>>>>>>>>>>>>
> >>>>>>>>>>>>>>>>>> This patch adds two new le16 fields to common
> >>>>>>>>>>>>>>>>>> configuration structure to support
> >>>>>>>>>>>>>>>>>> VIRTIO_F_QUEUE_STATE in PCI transport
> >>>>>> layer.
> >>>>>>>>>>>>>>>>>> Signed-off-by: Zhu Lingshan <lingshan.zhu@intel.com>
> >>>>>>>>>>>>>>>>>> ---
> >>>>>>>>>>>>>>>>>>           transport-pci.tex | 18 ++++++++++++++++++
> >>>>>>>>>>>>>>>>>>           1 file changed, 18 insertions(+)
> >>>>>>>>>>>>>>>>>>
> >>>>>>>>>>>>>>>>>> diff --git a/transport-pci.tex b/transport-pci.tex
> >>>>>>>>>>>>>>>>>> index
> >>>>>>>>>>>>>>>>>> a5c6719..3161519 100644
> >>>>>>>>>>>>>>>>>> --- a/transport-pci.tex
> >>>>>>>>>>>>>>>>>> +++ b/transport-pci.tex
> >>>>>>>>>>>>>>>>>> @@ -325,6 +325,10 @@ \subsubsection{Common
> >>>> configuration
> >>>>>>>>>>>>>> structure
> >>>>>>>>>>>>>>>>>> layout}\label{sec:Virtio Transport
> >>>>>>>>>>>>>>>>>>                   /* About the administration virtqueue. */
> >>>>>>>>>>>>>>>>>>                   le16 admin_queue_index;         /* read-only for
> >> driver
> >>>>>> */
> >>>>>>>>>>>>>>>>>>                   le16 admin_queue_num;         /* read-only for
> >> driver
> >>>>>> */
> >>>>>>>>>>>>>>>>>> +
> >>>>>>>>>>>>>>>>>> +	/* Virtqueue state */
> >>>>>>>>>>>>>>>>>> +        le16 queue_avail_state;         /* read-write */
> >>>>>>>>>>>>>>>>>> +        le16 queue_used_state;          /* read-write */
> >>>>>>>>>>>>>>>>> This tiny interface for 128 virtio net queues through
> >>>>>>>>>>>>>>>>> register read writes, does
> >>>>>>>>>>>>>>>> not work effectively.
> >>>>>>>>>>>>>>>>> There are inflight out of order descriptors for block also.
> >>>>>>>>>>>>>>>>> Hence toy registers like this do not work.
> >>>>>>>>>>>>>>>> Do you know there is a queue_select? Why this does not
> >> work?
> >>>>>>>>>>>>>>>> Do you know how other queue related fields work?
> >>>>>>>>>>>>>>> :)
> >>>>>>>>>>>>>>> Yes. If you notice queue_reset related critical spec bug
> >>>>>>>>>>>>>>> fix was done when it
> >>>>>>>>>>>>>> was introduced so that live migration can _actually_ work.
> >>>>>>>>>>>>>>> When queue_select is done for 128 queues serially, it
> >>>>>>>>>>>>>>> take a lot of time to
> >>>>>>>>>>>>>> read those slow register interface for this + inflight
> >>>>>>>>>>>>>> descriptors +
> >>>>>> more.
> >>>>>>>>>>>>>> interesting, virtio work in this pattern for many years, right?
> >>>>>>>>>>>>> All these years 400Gbps and 800Gbps virtio was not
> >>>>>>>>>>>>> present, number of
> >>>>>>>>>>>> queues were not in hw.
> >>>>>>>>>>>> The registers are control path in config space, how 400G or
> >>>>>>>>>>>> 800G
> >>>>>> affect??
> >>>>>>>>>>> Because those are the one in practice requires large number of
> VQs.
> >>>>>>>>>>>
> >>>>>>>>>>> You are asking per VQ register commands to modify things
> >>>>>>>>>>> dynamically via
> >>>>>>>>>> this one vq at a time, serializing all the operations.
> >>>>>>>>>>> It does not scale well with high q count.
> >>>>>>>>>> This is not dynamically, it only happens when SUSPEND and
> RESUME.
> >>>>>>>>>> This is the same mechanism how virtio initialize a virtqueue,
> >>>>>>>>>> working for many years.
> >>>>>>>>> No. when virtio driver initializes it for the first time,
> >>>>>>>>> there is no active traffic
> >>>>>>>> that gets lost.
> >>>>>>>>> This is because the interface is not yet up and not part of
> >>>>>>>>> the network
> >>>> yet.
> >>>>>>>>> The resume must be fast enough, because the remote node is
> >>>>>>>>> sending
> >>>>>>>> packets.
> >>>>>>>>> Hence it is different from driver init time queue enable.
> >>>>>>>> I am not sure any packets arrive before a link announce at the
> >>>>>>>> destination
> >>>>>> side.
> >>>>>>> I think it can.
> >>>>>>> Because there is no notification of member device link down
> >>>>>>> intimation to
> >>>>>> remote side.
> >>>>>>> The L4 and L5 protocols have no knowledge that node which they
> >>>>>>> are
> >>>>>> interacting is behind some layers of switches.
> >>>>>>> So keeping this time low is desired.
> >>>>>> The NIC should broad cast itself first, so that other peers in
> >>>>>> the network know(for example its mac to route it) how to send a
> >>>>>> message to
> >> it.
> >>>>>> This is necessary, for example VIRTIO_NET_F_GUEST_ANNOUNCE,
> >>>>>> similar mechanism work for in-marketing productions for years.
> >>>>>>
> >>>>>> This is out of the topic anyway.
> >>>>>>>>>>>> See the virtio common cfg, you will find the max number of
> >>>>>>>>>>>> vqs is there, num_queues.
> >>>>>>>>>>> :)
> >>>>>>>>>>> Sure. those values at high q count affects.
> >>>>>>>>>> the driver need to initialize them anyway.
> >>>>>>>>> That is before the traffic starts from remote end.
> >>>>>>>> see above, that needs a link announce and this is after
> >>>>>>>> re-initialization
> >>>>>>>>>>>>> Device didnât support LM.
> >>>>>>>>>>>>> Many limitations existed all these years and TC is
> >>>>>>>>>>>>> improving and expanding
> >>>>>>>>>>>> them.
> >>>>>>>>>>>>> So all these years do not matter.
> >>>>>>>>>>>> Not sure what are you talking about, haven't we initialize
> >>>>>>>>>>>> the device and vqs in config space for years?????? What's
> >>>>>>>>>>>> wrong with this
> >>>>>>>> mechanism?
> >>>>>>>>>>>> Are you questioning virito-pci fundamentals???
> >>>>>>>>>>> Donât point to in-efficient past to establish similar in-efficient
> future.
> >>>>>>>>>> interesting, you know this is a one-time thing, right?
> >>>>>>>>>> and you are aware of this has been there for years.
> >>>>>>>>>>>>>>>> Like how to set a queue size and enable it?
> >>>>>>>>>>>>>>> Those are meant to be used before DRIVER_OK stage as
> >>>>>>>>>>>>>>> they are init time
> >>>>>>>>>>>>>> registers.
> >>>>>>>>>>>>>>> Not to keep abusing them..
> >>>>>>>>>>>>>> don't you need to set queue_size at the destination side?
> >>>>>>>>>>>>> No.
> >>>>>>>>>>>>> But the src/dst does not matter.
> >>>>>>>>>>>>> Queue_size to be set before DRIVER_OK like rest of the
> >>>>>>>>>>>>> registers, as all
> >>>>>>>>>>>> queues must be created before the driver_ok phase.
> >>>>>>>>>>>>> Queue_reset was last moment exception.
> >>>>>>>>>>>> create a queue? Nvidia specific?
> >>>>>>>>>>>>
> >>>>>>>>>>> Huh. No.
> >>>>>>>>>>> Do git log and realize what happened with queue_reset.
> >>>>>>>>>> You didn't answer the question, does the spec even has
> >>>>>>>>>> defined "create a
> >>>>>>>> vq"?
> >>>>>>>>> Enabled/created = tomato/tomato when discussing the spec in
> >>>>>>>>> non-normative
> >>>>>>>> email conversation.
> >>>>>>>>> It's irrelevant.
> >>>>>>>> Then lets not debate on this enable a vq or create a vq anymore
> >>>>>>>>> All I am saying is, when we know the limitations of the
> >>>>>>>>> transport and when industry is forwarding to not introduced
> >>>>>>>>> more and more on-die register
> >>>>>>>> for once in lifetime work of device migration, we just use the
> >>>>>>>> optimal command and queue interface that is native to virtio.
> >>>>>>>> PCI config space has its own limitations, and admin vq has its
> >>>>>>>> advantages, but that does not apply to all use cases.
> >>>>>>>>
> >>>>>>> There was a recent work done emulating the SR-IOV cap and
> >>>>>>> allowing VM to
> >>>>>> enable SR-IOV in [1].
> >>>>>>> This is the option I mentioned few weeks ago.
> >>>>>>>
> >>>>>>> So with admin commands and admin virtqueues, even nested model
> >>>>>>> will work
> >>>>>> using [1].
> >>>>>>> [1]
> >>>>>>> https://netdevconf.info/0x17/sessions/talk/unleashing-sr-iov-off
> >>>>>>> lo
> >>>>>>> ad
> >>>>>>> -o
> >>>>>>> n-virtual-machines.html
> >>>>>> We should take this into consideration once it is standardized in
> >>>>>> the spec, maybe not now, there can always be many workarounds to
> >>>>>> solve one
> >>>> problem.
> >>>>> Sure, until that point the admin commands are able to suffice the
> >>>>> need
> >> well.
> >>>>> And when the spec changes in transport occurs (if needed), current
> >>>>> admin
> >>>> command and admin vq also fits very well that will follow above [1].
> >>>> we have pointed lots of problems for admin vq based live migration
> >>>> proposal, I won't repeat them here
> >>> I donât see any.
> >>> Nested is already solved using above.
> >> I don't see how, do you mind to work out the patches?
> > Once the base series is completed, nested cases can be addressed.
> > I wont be able to work on the patches for it until we finish for the first level
> virtualization.
> As you know, nested is supported well in current virtio, so please don't break it.

And same comment repeats. ð
Expect same response...
Sorry, no virtio specification does not support device migration today.
Nothing is broken by adding new features. 

Above [1] has the right proposal that Jason's paper pointed out. Please use it.