hw/9pfs: Use ioeventfd for 9p

With ioeventfd:
[root@qemu-img-64 storage]# dd if=/dev/zero of=/storage/testx bs=8k count=131072 oflag=direct
131072+0 records in
131072+0 records out
1073741824 bytes (1.1 GB) copied, 26.767 s, 40.1 MB/s

Without:
[root@qemu-img-64 storage]# dd if=/dev/zero of=/storage/testx bs=8k count=131072 oflag=direct
131072+0 records in
131072+0 records out
1073741824 bytes (1.1 GB) copied, 65.3361 s, 16.4 MB/s
Reviewed-by: NStefan Hajnoczi <stefanha@linux.vnet.ibm.com>
Signed-off-by: NAneesh Kumar K.V <aneesh.kumar@linux.vnet.ibm.com>

hw/9pfs/virtio-9p-device.c

@@ -169,6 +169,8 @@ static PCIDeviceInfo virtio_9p_info = {
     .revision  = VIRTIO_PCI_ABI_VERSION,
     .class_id  = 0x2,
     .qdev.props = (Property[]) {
+        DEFINE_PROP_BIT("ioeventfd", VirtIOPCIProxy, flags,
+                        VIRTIO_PCI_FLAG_USE_IOEVENTFD_BIT, true),
         DEFINE_PROP_UINT32("vectors", VirtIOPCIProxy, nvectors, 2),
         DEFINE_VIRTIO_COMMON_FEATURES(VirtIOPCIProxy, host_features),
         DEFINE_PROP_STRING("mount_tag", VirtIOPCIProxy, fsconf.tag),

hw/virtio-pci.c

@@ -83,11 +83,6 @@
 /* Flags track per-device state like workarounds for quirks in older guests. */
 #define VIRTIO_PCI_FLAG_BUS_MASTER_BUG  (1 << 0)
 
-/* Performance improves when virtqueue kick processing is decoupled from the
- * vcpu thread using ioeventfd for some devices. */
-#define VIRTIO_PCI_FLAG_USE_IOEVENTFD_BIT 1
-#define VIRTIO_PCI_FLAG_USE_IOEVENTFD   (1 << VIRTIO_PCI_FLAG_USE_IOEVENTFD_BIT)
-
 /* QEMU doesn't strictly need write barriers since everything runs in
  * lock-step.  We'll leave the calls to wmb() in though to make it obvious for
  * KVM or if kqemu gets SMP support.

hw/virtio-pci.h

@@ -18,6 +18,11 @@
 #include "virtio-net.h"
 #include "virtio-serial.h"
 
+/* Performance improves when virtqueue kick processing is decoupled from the
+ * vcpu thread using ioeventfd for some devices. */
+#define VIRTIO_PCI_FLAG_USE_IOEVENTFD_BIT 1
+#define VIRTIO_PCI_FLAG_USE_IOEVENTFD   (1 << VIRTIO_PCI_FLAG_USE_IOEVENTFD_BIT)
+
 typedef struct {
     PCIDevice pci_dev;
     VirtIODevice *vdev;