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>
diff --git a/include/linux/virtio_ring.h b/include/linux/virtio_ring.h
index 36be0f6..e338730 100644
--- a/include/linux/virtio_ring.h
+++ b/include/linux/virtio_ring.h
@@ -168,6 +168,7 @@
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),