virtio: harsher barriers for rpmsg.

We were cheating with our barriers; using the smp ones rather than the
real device ones.  That was fine, until rpmsg came along, which is
used to talk to a real device (a non-SMP CPU).

Unfortunately, just putting back the real barriers (reverting
d57ed95d) causes a performance regression on virtio-pci.  In
particular, Amos reports netbench's TCP_RR over virtio_net CPU
utilization increased up to 35% while throughput went down by up to
14%.

By comparison, this branch is in the noise.

Reference: https://lkml.org/lkml/2011/12/11/22

Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>

1 files changed, 2 insertions, 2 deletions

diff --git a/drivers/virtio/virtio_mmio.c b/drivers/virtio/virtio_mmio.c
index 0269717436af..01d6dc250d5c 100644
--- a/drivers/virtio/virtio_mmio.c
+++ b/drivers/virtio/virtio_mmio.c
@@ -310,8 +310,8 @@ static struct virtqueue *vm_setup_vq(struct virtio_device *vdev, unsigned index,
                         vm_dev->base + VIRTIO_MMIO_QUEUE_PFN);
 
         /* Create the vring */
-        vq = vring_new_virtqueue(info->num, VIRTIO_MMIO_VRING_ALIGN,
-                                 vdev, info->queue, vm_notify, callback, name);
+        vq = vring_new_virtqueue(info->num, VIRTIO_MMIO_VRING_ALIGN, vdev,
+                                 true, info->queue, vm_notify, callback, name);
         if (!vq) {
                 err = -ENOMEM;
                 goto error_new_virtqueue;