Re: [PATCH] virtio: fix idx in used ring retrieved only once

[Yuanhan Liu <yuanhan.liu@linux.intel.com>]

On Thu, Jun 16, 2016 at 02:30:37AM +0800, Huawei Xie wrote:
> -	while (vq->vq_used_cons_idx != vq->vq_ring.used->idx) {
> +	while (VIRTQUEUE_NUSED(vq)) {
>  		uint32_t idx, desc_idx, used_idx;
>  		struct vring_used_elem *uep;
>  
> diff --git a/drivers/net/virtio/virtio_ring.h b/drivers/net/virtio/virtio_ring.h
> index 447760a..fcecc16 100644
> --- a/drivers/net/virtio/virtio_ring.h
> +++ b/drivers/net/virtio/virtio_ring.h
> @@ -79,7 +79,7 @@ struct vring_used_elem {
>  
>  struct vring_used {
>  	uint16_t flags;
> -	uint16_t idx;
> +	volatile uint16_t idx;
>  	struct vring_used_elem ring[0];
>  };
>  
> diff --git a/drivers/net/virtio/virtio_rxtx_simple.c b/drivers/net/virtio/virtio_rxtx_simple.c
> index 7b50119..a0ef8d2 100644
> --- a/drivers/net/virtio/virtio_rxtx_simple.c
> +++ b/drivers/net/virtio/virtio_rxtx_simple.c
> @@ -184,8 +184,7 @@ virtio_recv_pkts_vec(void *rx_queue, struct rte_mbuf **rx_pkts,
>  	if (unlikely(nb_pkts < RTE_VIRTIO_DESC_PER_LOOP))
>  		return 0;
>  
> -	nb_used = *(volatile uint16_t *)&vq->vq_ring.used->idx -
> -		vq->vq_used_cons_idx;
> +	nb_used = vq->vq_ring.used->idx - vq->vq_used_cons_idx;

How about replacing it with VIRTQUEUE_NUSED here?

	--yliu