RE: [PATCH 2/5] Introduce VIRTIO_F_ADMIN_VQ_INDIRECT_DESC/VIRTIO_F_ADMIN_VQ_IN_ORDER

[Parav Pandit <parav@nvidia.com>]

> From: Michael S. Tsirkin <mst@redhat.com>
> Sent: Wednesday, January 26, 2022 7:42 PM
> 
> On Wed, Jan 26, 2022 at 01:29:27PM +0000, Parav Pandit wrote:
> >
> > > From: Michael S. Tsirkin <mst@redhat.com>
> > > Sent: Tuesday, January 25, 2022 5:39 PM
> >
> > > >
> > > > So you do agree that managing a managed
> > > > (create/destroy/setup/etc...) will be done using the AQ of the managing
> device ?
> > >
> > > I think Jason asked that the management commands are split from the
> > > queue itself, such that they can be implemented in more ways down the
> road.
> >
> > Admin commands involved DMA. And also multiple commands can be
> enqueued to the device.
> > I don't see any other construct in the spec other than vq that enables driver
> and device to achieve both.
> > Hence split the queue from command is very weird for spec to do.
> 
>  VIRTIO_PCI_CAP_SHARED_MEMORY_CFG can do this.
>
Device needs to always have shared memory region always in available range for driver to read.
Driver still needs to copy data from shared region to own memory.
How DMA Can be done in the host driver PA using shared memory region?

In future when SIOV occurs, each new SIOV SF/ADI will require new window in the shared regions exposed statically during PCI discovery time.
So it doesn't scale.
  
> 
> > A recent addition like virtio_fs_req didnât adopt this suggestion.
> >
> > If we just want to split so that admin commands can be transported via non
> admin queue, we should remove below line from spec:
> >
> > "The Admin command set defines the commands that may be issued only to
> the admin virtqueue"
> 
> sure
> 
> > And reword it as below,
> >
> > The Admin command set defines the commands to manipulate various
> features/attributes of another device within the same group...
> > When VIRTIO_F_ADMIN_VQ feature is negotiated, admin commands must
> be transported through the admin queue.
> >
> > Looks ok?
> 
> I see no problem with that.

Since we agree for this, I considered AQ vs no_AQ as closed topic?