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

[Max Gurtovoy <mgurtovoy@nvidia.com>]

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?
>
>
> > ---
> >   content.tex | 3 +++
> >   1 file changed, 3 insertions(+)
> >
> > diff --git a/content.tex b/content.tex
> > index 0ae4b68..e9c2383 100644
> > --- a/content.tex
> > +++ b/content.tex
> > @@ -3034,6 +3034,7 @@ \subsection{Virtqueues}\label{sec:Device Types / Network Device / Virtqueues}
> >   \item[2(N-1)] receiveqN
> >   \item[2(N-1)+1] transmitqN
> >   \item[2N] controlq
> > +\item[2N + 1] adminq (or \textbf{2N} in case VIRTIO_NET_F_CTRL_VQ is not set)
> >   \end{description}
> >   
> >    N=1 if neither VIRTIO_NET_F_MQ nor VIRTIO_NET_F_RSS are negotiated, otherwise N is set by
> > @@ -3041,6 +3042,8 @@ \subsection{Virtqueues}\label{sec:Device Types / Network Device / Virtqueues}
> >   
> >    controlq only exists if VIRTIO_NET_F_CTRL_VQ set.
> >   
> > + adminq only exists if VIRTIO_F_ADMIN_VQ set.
> > +
> >   \subsection{Feature bits}\label{sec:Device Types / Network Device / Feature bits}
> >   
> >   \begin{description}
> > --
> > 2.21.0