Re: [RFC v2 12/13] vdpa: preemptive kick at enable

[Jason Wang]

On Fri, Jan 13, 2023 at 1:27 AM Eugenio Pérez <eperezma@redhat.com> wrote:
>
> Spuriously kick the destination device's queue so it knows in case there
> are new descriptors.
>
> RFC: This is somehow a gray area. The guest may have placed descriptors
> in a virtqueue but not kicked it, so it might be surprised if the device
> starts processing it.

So I think this is kind of the work of the vDPA parent. For the parent
that needs this trick, we should do it in the parent driver.

Thanks

>
> However, that information is not in the migration stream and it should
> be an edge case anyhow, being resilient to parallel notifications from
> the guest.
>
> Signed-off-by: Eugenio Pérez <eperezma@redhat.com>
> ---
>  hw/virtio/vhost-vdpa.c | 5 +++++
>  1 file changed, 5 insertions(+)
>
> diff --git a/hw/virtio/vhost-vdpa.c b/hw/virtio/vhost-vdpa.c
> index 40b7e8706a..dff94355dd 100644
> --- a/hw/virtio/vhost-vdpa.c
> +++ b/hw/virtio/vhost-vdpa.c
> @@ -732,11 +732,16 @@ static int vhost_vdpa_set_vring_ready(struct vhost_dev 
> *dev, int ready)
>      }
>      trace_vhost_vdpa_set_vring_ready(dev);
>      for (i = 0; i < dev->nvqs; ++i) {
> +        VirtQueue *vq;
>          struct vhost_vring_state state = {
>              .index = dev->vq_index + i,
>              .num = 1,
>          };
>          vhost_vdpa_call(dev, VHOST_VDPA_SET_VRING_ENABLE, &state);
> +
> +        /* Preemptive kick */
> +        vq = virtio_get_queue(dev->vdev, dev->vq_index + i);
> +        event_notifier_set(virtio_queue_get_host_notifier(vq));
>      }
>      return 0;
>  }
> --
> 2.31.1
>