[virtio-comment] Re: [PATCH 0/2] Selective queue enabling

["Michael S. Tsirkin" <mst@redhat.com>]

On Tue, Jun 06, 2023 at 07:55:09PM +0200, Eugenio Pérez wrote:
> This series allows the driver to start the device (as set DRIVER_OK) with only
> some queues enabled, and then enable another queues later.
> 
> This is the current way to migrate net device state through control
> virtqueue, in a software assisted framework with vDPA:
> * First, only net CVQ is enabled at DRIVER_OK
> * All the control commands (mac address, mq, etc) needed for the device
> to behave the same as the source of migration are sent
> * Finally all the dataplane queues are enabled.

In my opinion, this is somewhat problematic. Specifically, currently
devices tend to deduce how many queues are needed by looking
at the state at DRIVER_OK time.  
                                 
Question: what is wrong with enabling queues initially and then
doing a reset right after DRIVER_OK? You can even allocate
memory for just one queue (zeroing it out).

Granted this looks kind of ugly but side-steps this problem with
no need for spec changes.

> Eugenio Pérez (2):
>   virtio: introduce selective queue enabling
>   virtio: pci support virtqueue selective enabling
> 
>  content.tex       | 15 +++++++++++++--
>  transport-pci.tex |  4 ++++
>  2 files changed, 17 insertions(+), 2 deletions(-)
> 
> -- 
> 2.31.1
> 


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