[PATCH 29/34] Revert "virtio_ring: Update weak barriers to use dma_wmb/rmb"

Michael S. Tsirkin
2015-12-30T13:26:25Z

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@infradead.org>
Cc: Alexander Duyck <alexander.duyck@gmail.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
---
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