Re: [PATCH RFC v7 4/8] Add admin_queue_index register to PCI common configuration structure

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

On Fri, Aug 19, 2022 at 08:28:41AM +0800, Jason Wang wrote:
> On Thu, Aug 18, 2022 at 4:55 PM Max Gurtovoy <mgurtovoy@nvidia.com> wrote:
> >
> >
> > On 8/18/2022 11:49 AM, Jason Wang wrote:
> > > On Sat, Aug 13, 2022 at 1:19 AM Michael S. Tsirkin <mst@redhat.com> wrote:
> > >> From: Max Gurtovoy <mgurtovoy@nvidia.com>
> > >>
> > >> This new register will be used for querying the index of the admin
> > >> virtqueue of a virtio device. To configure, reset or enable the admin
> > >> virtqueue, the driver should follow existing queue configuration/setup
> > >> sequence.
> > >>
> > >> Signed-off-by: Max Gurtovoy <mgurtovoy@nvidia.com>
> > >> Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
> > >> ---
> > >>   content.tex | 14 ++++++++++++++
> > >>   1 file changed, 14 insertions(+)
> > >>
> > >> diff --git a/content.tex b/content.tex
> > >> index 6ce1c07..297cb4a 100644
> > >> --- a/content.tex
> > >> +++ b/content.tex
> > >> @@ -904,6 +904,9 @@ \subsubsection{Common configuration structure layout}\label{sec:Virtio Transport
> > >>           le64 queue_device;              /* read-write */
> > >>           le16 queue_notify_data;         /* read-only for driver */
> > >>           le16 queue_reset;               /* read-write */
> > >> +
> > >> +        /* About the administration virtqueue. */
> > >> +        le16 admin_queue_index;         /* read-only for driver */
> > > Is there a chance that we may have multiple admin virtqueues?
> >
> > No, same as we probably can't have multiple ctrl virtqueues..
> 
> For control virtqueue, it's technically possible but doesn't have too
> much value.
> 
> But for admin virtqueue we can:
> 
> admin vq 1: group 1
> admin vq 2: group 2
> 
> ?
> 
> Thanks

I don't see how *that* will solve scalability issues, e.g. a group might have
10k devices. Just allowing submitting commands to any of multiple admin
vqs might make sense. I'm looking for a clean interface to expose that
though and don't see it yet.


> >
> >
> > >
> > > Thanks
> > >
> > >
> > >>   };
> > >>   \end{lstlisting}
> > >>
> > >> @@ -989,6 +992,10 @@ \subsubsection{Common configuration structure layout}\label{sec:Virtio Transport
> > >>           This field exists only if VIRTIO_F_RING_RESET has been
> > >>           negotiated. (see \ref{sec:Basic Facilities of a Virtio Device / Virtqueues / Virtqueue Reset}).
> > >>
> > >> +\item[\field{admin_queue_index}]
> > >> +        The device uses this to report the index of the administration virtqueue.
> > >> +        This field is valid only if VIRTIO_F_ADMIN_VQ has been negotiated.
> > >> +
> > >>   \end{description}
> > >>
> > >>   \devicenormative{\paragraph}{Common configuration structure layout}{Virtio Transport Options / Virtio Over PCI Bus / PCI Device Layout / Common configuration structure layout}
> > >> @@ -1075,6 +1082,9 @@ \subsubsection{Common configuration structure layout}\label{sec:Virtio Transport
> > >>   were used before the queue reset.
> > >>   (see \ref{sec:Basic Facilities of a Virtio Device / Virtqueues / Virtqueue Reset}).
> > >>
> > >> +If VIRTIO_F_ADMIN_VQ has been negotiated, the driver MUST
> > >> +configure the administration virtqueue using the value of \field{admin_queue_index}.
> > >> +
> > >>   \subsubsection{Notification structure layout}\label{sec:Virtio Transport Options / Virtio Over PCI Bus / PCI Device Layout / Notification capability}
> > >>
> > >>   The notification location is found using the VIRTIO_PCI_CAP_NOTIFY_CFG
> > >> @@ -6947,6 +6957,10 @@ \chapter{Reserved Feature Bits}\label{sec:Reserved Feature Bits}
> > >>     See \ref{sec:Basic Facilities of a Virtio Device / Virtqueues / Virtqueue Reset}.
> > >>
> > >>     \item[VIRTIO_F_ADMIN_VQ (41)] This feature indicates that an administration virtqueue is supported.
> > >> +  At the moment this feature is only supported for devices using
> > >> +  \ref{sec:Virtio Transport Options / Virtio Over PCI
> > >> +         Bus}~\nameref{sec:Virtio Transport Options / Virtio Over PCI Bus}
> > >> +         as the transport.
> > >>
> > >>   \end{description}
> > >>
> > >> --
> > >> MST
> > >>
> >