RE: [PATCH 4/5] virtio-net: add support for VIRTIO_F_ADMIN_VQ

[Parav Pandit <parav@nvidia.com>]

> From: Max Gurtovoy <mgurtovoy@nvidia.com>
> Sent: Sunday, January 16, 2022 3:18 PM
> 
> 
> On 1/13/2022 7:56 PM, Michael S. Tsirkin wrote:
> > On Thu, Jan 13, 2022 at 04:51:02PM +0200, Max Gurtovoy wrote:
> >> Set the relevant index in case of VIRTIO_F_ADMIN_VQ negotiation.
> >>
> >> Reviewed-by: Parav Pandit <parav@nvidia.com>
> >> Signed-off-by: Max Gurtovoy <mgurtovoy@nvidia.com>
> > So admin VQ # is only known when all features are negotiated.
> 
> No. The driver should see if VIRTIO_NET_F_CTRL_VQ/VIRTIO_F_ADMIN_VQ
> are set by the device.
> 
> Negotiation is not a must.
> 
> Lets say CTRL_VQ is supported by the device and driver A would like to use it
> and driver B wouldn't like to use it - in both cases the admiq VQ # would be 2N
> + 1.
> 
> > Which is quite annoying if hypervisor wants to partition things e.g.
> > handling admin q in process and handling vqs by an external process or
> > by hardware.
> >
> > I think we can allow devices to set the VQ# for the admin queue
> > instead. Would that work?
Number of MSI-X configuration and number of VQs config are two different, though it has strong correlation.
Configuring number of queues seems a very device specific configuration (even though num_queues is generic field in struct virtio_pci_common_cfg).

So num VQ configuration is a different command likely combined with other device specific config such as mac or rss or others.