net/virtio: improve perf via one-way barrier on avail flag

[dpdk.git] / drivers / net / virtio / virtio_user / virtio_user_dev.c

diff --git a/drivers/net/virtio/virtio_user/virtio_user_dev.c b/drivers/net/virtio/virtio_user/virtio_user_dev.c
index fab87eb..7911c39 100644 (file)
--- a/drivers/net/virtio/virtio_user/virtio_user_dev.c
+++ b/drivers/net/virtio/virtio_user/virtio_user_dev.c
@@ -624,7 +624,7 @@ virtio_user_handle_ctrl_msg(struct virtio_user_dev *dev, struct vring *vring,
 static inline int
 desc_is_avail(struct vring_packed_desc *desc, bool wrap_counter)
 {
-       uint16_t flags = desc->flags;
+       uint16_t flags = __atomic_load_n(&desc->flags, __ATOMIC_ACQUIRE);
 
        return wrap_counter == !!(flags & VRING_PACKED_DESC_F_AVAIL) &&
                wrap_counter != !!(flags & VRING_PACKED_DESC_F_USED);
@@ -684,6 +684,10 @@ virtio_user_handle_cq_packed(struct virtio_user_dev *dev, uint16_t queue_idx)
        struct vring_packed *vring = &dev->packed_vrings[queue_idx];
        uint16_t n_descs, flags;
 
+       /* Perform a load-acquire barrier in desc_is_avail to
+        * enforce the ordering between desc flags and desc
+        * content.
+        */
        while (desc_is_avail(&vring->desc[vq->used_idx],
                             vq->used_wrap_counter)) {