[PATCH] vhost: don't set vring call if no enabled msix

[lyx634449800 <yuxue.liu@jaguarmicro.com>]

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 virtual machine operating system, even if the virtio device
does not use msix interrupts, vhost still sets vring call fd. This
leads to unnecessary performance overhead. If the guest driver does
not enable msix capability (e.g virtio-net pmd), we should also
check and clear the vring call fd.

Signed-off-by: Yuxue Liu <yuxue.liu@jaguarmicro.com>
---
 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