Re: [Qemu-devel] [PATCH] virtio/vhost: drop unnecessary VHOST_SET_VRING call

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

On Wed, Aug 12, 2015 at 02:10:56PM +0300, Marcel Apfelbaum wrote:
> On 08/12/2015 01:34 PM, Michael S. Tsirkin wrote:
> >On Wed, Aug 12, 2015 at 01:19:51PM +0300, Marcel Apfelbaum wrote:
> >>No need to send VHOST_SET_VRING_CALL to backend
> >>before the negotiation with the guest is finished.
> >>
> >>Signed-off-by: Marcel Apfelbaum <marcel@redhat.com>
> >
> >Well - we do need to set it to the masked notifier initially to avoid
> >losing events.  You can't just drop it - need to move this call
> >somewhere else.
> What do we need to set?
> I just dropped the call to VHOST_SET_VRING_CALL.
> 
> Thanks,
> Marcel

We use two eventfds: masked and unmasked one.
We switch dynamically dependent on msi mask value.
Code assumes we start out masked, so we need to match that.


> >
> >>---
> >>  hw/virtio/vhost.c | 13 +------------
> >>  1 file changed, 1 insertion(+), 12 deletions(-)
> >>
> >>diff --git a/hw/virtio/vhost.c b/hw/virtio/vhost.c
> >>index 2712c6f..b448542 100644
> >>--- a/hw/virtio/vhost.c
> >>+++ b/hw/virtio/vhost.c
> >>@@ -875,24 +875,13 @@ static void vhost_eventfd_del(MemoryListener *listener,
> >>  static int vhost_virtqueue_init(struct vhost_dev *dev,
> >>                                  struct vhost_virtqueue *vq, int n)
> >>  {
> >>-    struct vhost_vring_file file = {
> >>-        .index = n,
> >>-    };
> >>      int r = event_notifier_init(&vq->masked_notifier, 0);
> >>+
> >>      if (r < 0) {
> >>          return r;
> >>      }
> >>
> >>-    file.fd = event_notifier_get_fd(&vq->masked_notifier);
> >>-    r = dev->vhost_ops->vhost_call(dev, VHOST_SET_VRING_CALL, &file);
> >>-    if (r) {
> >>-        r = -errno;
> >>-        goto fail_call;
> >>-    }
> >>      return 0;
> >>-fail_call:
> >>-    event_notifier_cleanup(&vq->masked_notifier);
> >>-    return r;
> >>  }
> >>
> >>  static void vhost_virtqueue_cleanup(struct vhost_virtqueue *vq)
> >>--
> >>2.1.0