[PATCH] virtio-net: calculating proper msix vectors on init

[Jason Wang <jasowang@redhat.com>]

Currently, the default msix vectors for virtio-net-pci is 3 which is
obvious not suitable for multiqueue guest, so we depends on the user
or management tools to pass a correct vectors parameter. In fact, we
can simplifying this by calculating the number of vectors on realize.

Consider we have N queues, the number of vectors needed is 2*N + 2
(#queue pais + plus one config interrupt and control vq). We didn't
check whether or not host support control vq because it was added
unconditionally by qemu to avoid breaking legacy guests such as Minix.

Signed-off-by: Jason Wang <jasowang@redhat.com>
---
 hw/core/machine.c          | 1 +
 hw/virtio/virtio-net-pci.c | 8 +++++++-
 2 files changed, 8 insertions(+), 1 deletion(-)

diff --git a/hw/core/machine.c b/hw/core/machine.c
index 4386f57b5c..979133f8b7 100644
--- a/hw/core/machine.c
+++ b/hw/core/machine.c
@@ -39,6 +39,7 @@
 GlobalProperty hw_compat_5_2[] = {
     { "ICH9-LPC", "smm-compat", "on"},
     { "PIIX4_PM", "smm-compat", "on"},
+    { "virtio-net-pci", "vectors", "3"},
 };
 const size_t hw_compat_5_2_len = G_N_ELEMENTS(hw_compat_5_2);
 
diff --git a/hw/virtio/virtio-net-pci.c b/hw/virtio/virtio-net-pci.c
index 292d13d278..2894c46b66 100644
--- a/hw/virtio/virtio-net-pci.c
+++ b/hw/virtio/virtio-net-pci.c
@@ -41,7 +41,8 @@ struct VirtIONetPCI {
 static Property virtio_net_properties[] = {
     DEFINE_PROP_BIT("ioeventfd", VirtIOPCIProxy, flags,
                     VIRTIO_PCI_FLAG_USE_IOEVENTFD_BIT, true),
-    DEFINE_PROP_UINT32("vectors", VirtIOPCIProxy, nvectors, 3),
+    DEFINE_PROP_UINT32("vectors", VirtIOPCIProxy, nvectors,
+                       DEV_NVECTORS_UNSPECIFIED),
     DEFINE_PROP_END_OF_LIST(),
 };
 
@@ -50,6 +51,11 @@ static void virtio_net_pci_realize(VirtIOPCIProxy *vpci_dev, Error **errp)
     DeviceState *qdev = DEVICE(vpci_dev);
     VirtIONetPCI *dev = VIRTIO_NET_PCI(vpci_dev);
     DeviceState *vdev = DEVICE(&dev->vdev);
+    VirtIONet *net = VIRTIO_NET(vdev);
+
+    if (vpci_dev->nvectors == DEV_NVECTORS_UNSPECIFIED) {
+        vpci_dev->nvectors = 2 * MAX(net->nic_conf.peers.queues, 1) + 2;
+    }
 
     virtio_net_set_netclient_name(&dev->vdev, qdev->id,
                                   object_get_typename(OBJECT(qdev)));
-- 
2.24.3 (Apple Git-128)