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>

2 files changed, 3 insertions, 1 deletions

diff --git a/tools/virtio/linux/virtio.h b/tools/virtio/linux/virtio.h
index 669bcdd45805..953db2abf6b9 100644
--- a/tools/virtio/linux/virtio.h
+++ b/tools/virtio/linux/virtio.h
@@ -214,6 +214,7 @@ void *virtqueue_detach_unused_buf(struct virtqueue *vq);
 struct virtqueue *vring_new_virtqueue(unsigned int num,
                                       unsigned int vring_align,
                                       struct virtio_device *vdev,
+                                      bool weak_barriers,
                                       void *pages,
                                       void (*notify)(struct virtqueue *vq),
                                       void (*callback)(struct virtqueue *vq),
diff --git a/tools/virtio/virtio_test.c b/tools/virtio/virtio_test.c
index 74d3331bdaf9..0740284396c1 100644
--- a/tools/virtio/virtio_test.c
+++ b/tools/virtio/virtio_test.c
@@ -92,7 +92,8 @@ static void vq_info_add(struct vdev_info *dev, int num)
         assert(r >= 0);
         memset(info->ring, 0, vring_size(num, 4096));
         vring_init(&info->vring, num, info->ring, 4096);
-        info->vq = vring_new_virtqueue(info->vring.num, 4096, &dev->vdev, info->ring,
+        info->vq = vring_new_virtqueue(info->vring.num, 4096, &dev->vdev,
+                                       true, info->ring,
                                        vq_notify, vq_callback, "test");
         assert(info->vq);
         info->vq->priv = info;