[RFC v2 07/13] vhost: Avoid re-set masked notifier in shadow vq

["Eugenio Pérez" <eperezma@redhat.com>]

Since all the shadow virtqueue device is done in software, we can avoid
the write syscall.

Signed-off-by: Eugenio Pérez <eperezma@redhat.com>
---
 hw/virtio/vhost-shadow-virtqueue.c | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/hw/virtio/vhost-shadow-virtqueue.c b/hw/virtio/vhost-shadow-virtqueue.c
index 8f6ffa729a..b6bab438d6 100644
--- a/hw/virtio/vhost-shadow-virtqueue.c
+++ b/hw/virtio/vhost-shadow-virtqueue.c
@@ -41,6 +41,9 @@ typedef struct VhostShadowVirtqueue {
          * set when the masked notifier has no uses
          */
         QemuEvent is_free;
+
+        /* Avoid re-sending signals */
+        bool signaled;
     } masked_notifier;
 
     /* Virtio queue shadowing */
@@ -81,7 +84,8 @@ static void vhost_shadow_vq_handle_call_no_test(EventNotifier *n)
         unsigned n = virtio_get_queue_index(svq->vq);
         virtio_queue_invalidate_signalled_used(svq->vdev, n);
         virtio_notify_irqfd(svq->vdev, svq->vq);
-    } else {
+    } else if (!svq->masked_notifier.signaled) {
+        svq->masked_notifier.signaled = true;
         event_notifier_set(svq->masked_notifier.n);
     }
 
@@ -110,6 +114,7 @@ static void vhost_shadow_vq_handle_call(EventNotifier *n)
  */
 void vhost_shadow_vq_mask(VhostShadowVirtqueue *svq, EventNotifier *masked)
 {
+    svq->masked_notifier.signaled = false;
     qatomic_store_release(&svq->masked_notifier.n, masked);
 }
 
-- 
2.27.0