Re: [Qemu-devel] [[RFC v3 08/12] virtio: event suppression support for packed ring

[Jason Wang]

On 2018年10月15日 16:20, Wei Xu wrote:
> > > +static void virtio_queue_set_notification_packed(VirtQueue *vq, int enable)
> > > +{
> > > +    VRingPackedDescEvent e;
> > > +    VRingMemoryRegionCaches *caches;
> > > +
> > > +    rcu_read_lock();
> > > +    caches  = vring_get_region_caches(vq);
> > > +    vring_packed_event_read(vq->vdev, &caches->device, &e);
> > > +
> > > +    if (!enable) {
> > > +        e.flags = RING_EVENT_FLAGS_DISABLE;
> > > +        goto out;
> > > +    }
> > > +
> > > +    e.flags = RING_EVENT_FLAGS_ENABLE;
> > > +    if (virtio_vdev_has_feature(vq->vdev, VIRTIO_RING_F_EVENT_IDX)) {
> > > +        uint16_t off_wrap = vq->event_idx | vq->event_wrap_counter << 15;
> > Btw, why not just use shadow_avail_idx here?
> It is nice to do that but an issue here is that it is 'shadow_avail_idx' for
> Rx but 'used_idx' for Tx when setting up for a kick, haven't figured out a
> clear fix because it helps easier migration part work, any idea?
>
> Wei

I'm not sure I get the point here. Why need to care about used_idx when 
enabling guest kick?

Thanks