[PATCH v2] vhost: don't set vring call if guest notifiers is not enabled

[lyx634449800]

When conducting performance testing using testpmd in the guest os,
it was observed that the performance was lower compared to the
scenario of direct vfio-pci usage.

In the commit 96a3d98d2cdbd897ff5ab33427aa4cfb94077665, the author
provided a good solution. However, because the guest OS's
driver(e.g., virtio-net pmd) may not enable the msix capability, the
function k->query_guest_notifiers(qbus->parent) may return false,
resulting in the expected effect not being achieved. To address this
issue, modify the conditional statement.

Signed-off-by: Yuxue Liu <yuxue.liu@jaguarmicro.com>
---
V2: Update commit description and title

 hw/virtio/vhost.c | 16 +++++++++-------
 1 file changed, 9 insertions(+), 7 deletions(-)

diff --git a/hw/virtio/vhost.c b/hw/virtio/vhost.c
index f50180e60e..b972c84e67 100644
--- a/hw/virtio/vhost.c
+++ b/hw/virtio/vhost.c
@@ -1266,13 +1266,15 @@ int vhost_virtqueue_start(struct vhost_dev *dev,
         vhost_virtqueue_mask(dev, vdev, idx, false);
     }
 
-    if (k->query_guest_notifiers &&
-        k->query_guest_notifiers(qbus->parent) &&
-        virtio_queue_vector(vdev, idx) == VIRTIO_NO_VECTOR) {
-        file.fd = -1;
-        r = dev->vhost_ops->vhost_set_vring_call(dev, &file);
-        if (r) {
-            goto fail_vector;
+    if (k->query_guest_notifiers) {
+        if (!k->query_guest_notifiers(qbus->parent) ||
+            (k->query_guest_notifiers(qbus->parent) &&
+            virtio_queue_vector(vdev, idx) == VIRTIO_NO_VECTOR)) {
+            file.fd = -1;
+            r = dev->vhost_ops->vhost_set_vring_call(dev, &file);
+            if (r) {
+                goto fail_vector;
+            }
         }
     }
 
-- 
2.43.0