From mboxrd@z Thu Jan  1 00:00:00 1970
From: Yuanhan Liu <yuanhan.liu@linux.intel.com>
Subject: Re: [PATCH] virtio: fix idx in used ring retrieved only
 once
Date: Mon, 20 Jun 2016 14:27:10 +0800
Message-ID: <20160620062710.GE23111@yliu-dev.sh.intel.com>
References: <1466015437-36809-1-git-send-email-huawei.xie@intel.com>
Mime-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Cc: dev@dpdk.org, yuanhan.liu@intel.com, thomas.monjalon@6wind.com,
 mst@redhat.com, jianfeng.tan@intel.com, stephen@networkplumber.org,
 konstantin.ananyev@intel.com, bruce.richardson@intel.com
To: Huawei Xie <huawei.xie@intel.com>
Return-path: <dev-bounces@dpdk.org>
Received: from mga04.intel.com (mga04.intel.com [192.55.52.120])
 by dpdk.org (Postfix) with ESMTP id 94CA99621
 for <dev@dpdk.org>; Mon, 20 Jun 2016 08:27:50 +0200 (CEST)
Content-Disposition: inline
In-Reply-To: <1466015437-36809-1-git-send-email-huawei.xie@intel.com>
List-Id: patches and discussions about DPDK <dev.dpdk.org>
List-Unsubscribe: <http://dpdk.org/ml/options/dev>,
 <mailto:dev-request@dpdk.org?subject=unsubscribe>
List-Archive: <http://dpdk.org/ml/archives/dev/>
List-Post: <mailto:dev@dpdk.org>
List-Help: <mailto:dev-request@dpdk.org?subject=help>
List-Subscribe: <http://dpdk.org/ml/listinfo/dev>,
 <mailto:dev-request@dpdk.org?subject=subscribe>
Errors-To: dev-bounces@dpdk.org
Sender: "dev" <dev-bounces@dpdk.org>

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