Function virtqueue_nused

dpdk/drivers/net/virtio/virtqueue.h:421–446

virtqueue_nused has load-acquire or rte_io_rmb insed */

/* virtqueue_nused has load-acquire or rte_io_rmb insed */
static inline uint16_t
virtqueue_nused(const struct virtqueue *vq)
{
	uint16_t idx;

	if (vq->hw->weak_barriers) {
	/**
	 * x86 prefers to using rte_smp_rmb over __atomic_load_n as it
	 * reports a slightly better perf, which comes from the saved
	 * branch by the compiler.
	 * The if and else branches are identical with the smp and io
	 * barriers both defined as compiler barriers on x86.
	 */
#ifdef RTE_ARCH_X86_64
		idx = vq->vq_split.ring.used->idx;
		rte_smp_rmb();
#else
		idx = __atomic_load_n(&(vq)->vq_split.ring.used->idx,
				__ATOMIC_ACQUIRE);
#endif
	} else {
		idx = vq->vq_split.ring.used->idx;
		rte_io_rmb();
	}
	return idx - vq->vq_used_cons_idx;
}

void vq_ring_free_chain(struct virtqueue *vq, uint16_t desc_idx);
void vq_ring_free_chain_packed(struct virtqueue *vq, uint16_t used_idx);