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

[Zhu, Lingshan]

On 1/13/2023 10:31 AM, Jason Wang wrote:
> 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.
Agree, it looks easier implementing this in parent driver,
I can implement it in ifcvf set_vq_ready right now

Thanks
Zhu Lingshan
> 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