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

Zhu, Lingshan
2023-09-12T03:43:39Z

On 9/12/2023 11:35 AM, Jason Wang wrote:
> On Mon, Sep 11, 2023 at 6:15 PM Michael S. Tsirkin <mst@redhat.com> wrote:
>> On Mon, Sep 11, 2023 at 02:30:31PM +0800, Jason Wang wrote:
>>> Customers don't want to have admin stuff, SR-IOV or PASID in the guest
>>> in order to migrate a single virtio device in the nest.
>> Built an alternative facility to implement admin commands then.
> I wonder if it could be built in an efficient way. For example the
> length of admin commands is not fixed and we don't want to grow MMIO
> areas as the admin command, this will result in something like
> VIRTIO_PCI_CAP_PCI_CFG which is sub-optimal (much more registers
> accesses than simply introducing new fields in common cfg).
>
>> The advantage of admin commands is they are nicely contained.
> If it want to be contained it needs to duplicate the functionality of
> the existing facilities like common cfg and others (one example is to
> setup the virtqueue after migration). Otherwise during live migration,
> we will use both admin commands and existing configuration structure
> which will end up with more issues.
>
> As stated before, the best way is to decouple the basic facilities
> (states like index, inflight, dirty page) from a specific
> interface/transport and keep the flexibility at the transport layer.
> Transport layer can choose to stick to the existing interfaces or
> implement the admin commands. So we can have two ways in parallel:
>
> 1) live migration via the existing transport specific facilities, this
> allows us to reuse the existing interfaces with minimal extensions or
> take the advantages of the transport specific facilities like PASID
> 2) live migration via admin commands, but it needs to invent commands
> to access existing facilities which is just a new transport interface
> that LingShan is work (transport over admin commands)
>
> Instead of focusing on a solution that only works for a specific setup
> on a specific transport.
I totally agree
>
> Thanks
>
>> This proposal is way too intrusive.
>>
>> --
>> MST
>>