[dpdk-dev,v3] virtio: Fix vring entry number issue

  -- V1 change:
  Fix one issue in virtio TX: it needs one more vring descriptor to hold the virtio
  header when transmitting packets, it is used later to determine whether to free
  more entries from used vring.
 
  It fixes failing to transmit any packet with 1 segment in the circumstance of only
  1 descriptor in the vring free list.
 
-- V2 change:
  Refine description, 'vring descriptor' is more accurate than 'vring entry';
  Accordingly update test condition (it needs one more descriptor for virtio header) to
  put packets to transmit queue.

-- V3 change:
  Resolve compilation issue due to mbuf re-structure.

Signed-off-by: Changchun Ouyang <changchun.ouyang@intel.com>
---
 lib/librte_pmd_virtio/virtio_rxtx.c | 10 ++++++++--
 1 file changed, 8 insertions(+), 2 deletions(-)
  

Hi Olivier,

Any other comments for this v3 patch?

Thanks and regards,
Changchun

> -----Original Message-----
> From: Ouyang, Changchun
> Sent: Tuesday, October 14, 2014 11:13 PM
> To: dev@dpdk.org
> Cc: Cao, Waterman; Ouyang, Changchun
> Subject: [PATCH v3] virtio: Fix vring entry number issue
> 
> -- V1 change:
>   Fix one issue in virtio TX: it needs one more vring descriptor to hold the
> virtio
>   header when transmitting packets, it is used later to determine whether to
> free
>   more entries from used vring.
> 
>   It fixes failing to transmit any packet with 1 segment in the circumstance of
> only
>   1 descriptor in the vring free list.
> 
> -- V2 change:
>   Refine description, 'vring descriptor' is more accurate than 'vring entry';
>   Accordingly update test condition (it needs one more descriptor for virtio
> header) to
>   put packets to transmit queue.
> 
> -- V3 change:
>   Resolve compilation issue due to mbuf re-structure.
> 
> Signed-off-by: Changchun Ouyang <changchun.ouyang@intel.com>
> ---
>  lib/librte_pmd_virtio/virtio_rxtx.c | 10 ++++++++--
>  1 file changed, 8 insertions(+), 2 deletions(-)
> 
> diff --git a/lib/librte_pmd_virtio/virtio_rxtx.c
> b/lib/librte_pmd_virtio/virtio_rxtx.c
> index 0b10108..ac44c65 100644
> --- a/lib/librte_pmd_virtio/virtio_rxtx.c
> +++ b/lib/librte_pmd_virtio/virtio_rxtx.c
> @@ -699,7 +699,8 @@ virtio_xmit_pkts(void *tx_queue, struct rte_mbuf
> **tx_pkts, uint16_t nb_pkts)
>  	num = (uint16_t)(likely(nb_used < VIRTIO_MBUF_BURST_SZ) ?
> nb_used : VIRTIO_MBUF_BURST_SZ);
> 
>  	while (nb_tx < nb_pkts) {
> -		int need = tx_pkts[nb_tx]->pkt.nb_segs - txvq-
> >vq_free_cnt;
> +		/* Need one more descriptor for virtio header. */
> +		int need = tx_pkts[nb_tx]->nb_segs - txvq->vq_free_cnt + 1;
>  		int deq_cnt = RTE_MIN(need, (int)num);
> 
>  		num -= (deq_cnt > 0) ? deq_cnt : 0;
> @@ -708,7 +709,12 @@ virtio_xmit_pkts(void *tx_queue, struct rte_mbuf
> **tx_pkts, uint16_t nb_pkts)
>  			deq_cnt--;
>  		}
> 
> -		if (tx_pkts[nb_tx]->pkt.nb_segs <= txvq->vq_free_cnt) {
> +		need = (int)tx_pkts[nb_tx]->nb_segs - txvq->vq_free_cnt +
> 1;
> +		/*
> +		 * Zero or negative value indicates it has enough free
> +		 * decriptors to transmit.
> +		 */
> +		if (need <= 0) {
>  			txm = tx_pkts[nb_tx];
>  			/* Enqueue Packet buffers */
>  			error = virtqueue_enqueue_xmit(txvq, txm);
> --
> 1.8.4.2