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Subject[PATCH RFC 4/4] virtio: use dependent_ptr_mb
Use dependent_ptr_mb which is - on some architectures -
more light-weight than an rmb.

Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
---
drivers/virtio/virtio_ring.c | 6 ++++--
1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/drivers/virtio/virtio_ring.c b/drivers/virtio/virtio_ring.c
index 814b395007b2..2d320396eff8 100644
--- a/drivers/virtio/virtio_ring.c
+++ b/drivers/virtio/virtio_ring.c
@@ -702,6 +702,7 @@ void *virtqueue_get_buf_ctx(struct virtqueue *_vq, unsigned int *len,
void *ret;
unsigned int i;
u16 last_used;
+ bool more;

START_USE(vq);

@@ -710,14 +711,15 @@ void *virtqueue_get_buf_ctx(struct virtqueue *_vq, unsigned int *len,
return NULL;
}

- if (!more_used(vq)) {
+ more = more_used(vq);
+ if (!more) {
pr_debug("No more buffers in queue\n");
END_USE(vq);
return NULL;
}

/* Only get used array entries after they have been exposed by host. */
- virtio_rmb(vq->weak_barriers);
+ vq = dependent_ptr_mb(vq, more);

last_used = (vq->last_used_idx & (vq->vring.num - 1));
i = virtio32_to_cpu(_vq->vdev, vq->vring.used->ring[last_used].id);
--
MST
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