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/drivers/s390/kvm/kvm_virtio.c b/drivers/s390/kvm/kvm_virtio.c
index 8af868b..7bc1955 100644
--- a/drivers/s390/kvm/kvm_virtio.c
+++ b/drivers/s390/kvm/kvm_virtio.c
@@ -198,7 +198,7 @@
goto out;
vq = vring_new_virtqueue(config->num, KVM_S390_VIRTIO_RING_ALIGN,
- vdev, (void *) config->address,
+ vdev, true, (void *) config->address,
kvm_notify, callback, name);
if (!vq) {
err = -ENOMEM;