[Xen-devel] [PATCH v2 29/32] Revert "virtio_ring: Update weak barriers to use dma_wmb/rmb"

["Michael S. Tsirkin" <mst@xxxxxxxxxx>]

This reverts commit 9e1a27ea42691429e31f158cce6fc61bc79bb2e9.

While that commit optimizes !CONFIG_SMP, it mixes
up DMA and SMP concepts, making the code hard
to figure out.

A better way to optimize this is with the new __smp_XXX
barriers.

As a first step, go back to full rmb/wmb barriers
for !SMP.
We switch to __smp_XXX barriers in the next patch.

Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Cc: Alexander Duyck <alexander.duyck@xxxxxxxxx>
Signed-off-by: Michael S. Tsirkin <mst@xxxxxxxxxx>
---
 include/linux/virtio_ring.h | 23 +++++++++++++++++++----
 1 file changed, 19 insertions(+), 4 deletions(-)

diff --git a/include/linux/virtio_ring.h b/include/linux/virtio_ring.h
index 8e50888..67e06fe 100644
--- a/include/linux/virtio_ring.h
+++ b/include/linux/virtio_ring.h
@@ -21,20 +21,19 @@
  * actually quite cheap.
  */
 
+#ifdef CONFIG_SMP
 static inline void virtio_mb(bool weak_barriers)
 {
-#ifdef CONFIG_SMP
        if (weak_barriers)
                smp_mb();
        else
-#endif
                mb();
 }
 
 static inline void virtio_rmb(bool weak_barriers)
 {
        if (weak_barriers)
-               dma_rmb();
+               smp_rmb();
        else
                rmb();
 }
@@ -42,10 +41,26 @@ static inline void virtio_rmb(bool weak_barriers)
 static inline void virtio_wmb(bool weak_barriers)
 {
        if (weak_barriers)
-               dma_wmb();
+               smp_wmb();
        else
                wmb();
 }
+#else
+static inline void virtio_mb(bool weak_barriers)
+{
+       mb();
+}
+
+static inline void virtio_rmb(bool weak_barriers)
+{
+       rmb();
+}
+
+static inline void virtio_wmb(bool weak_barriers)
+{
+       wmb();
+}
+#endif
 
 struct virtio_device;
 struct virtqueue;
-- 
MST


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