[dpdk-dev] [PATCH 2/2] net/virtio: on demand cleanup when doing in order xmit

[Tiwei Bie]

On Tue, Aug 27, 2019 at 06:24:07PM +0800, Marvin Liu wrote:
> Check whether freed descriptors are enough before enqueue operation.
> If more space is needed, will try to cleanup used ring on demand. It
> can give more chances to cleanup used ring, thus help RFC2544 perf.
> 
> Signed-off-by: Marvin Liu <yong.liu at intel.com>
> ---
>  drivers/net/virtio/virtio_rxtx.c | 73 +++++++++++++++++++++++---------
>  1 file changed, 54 insertions(+), 19 deletions(-)
> 
> diff --git a/drivers/net/virtio/virtio_rxtx.c b/drivers/net/virtio/virtio_rxtx.c
> index 5d4ed524e..550b0aa62 100644
> --- a/drivers/net/virtio/virtio_rxtx.c
> +++ b/drivers/net/virtio/virtio_rxtx.c
> @@ -317,7 +317,7 @@ virtio_xmit_cleanup(struct virtqueue *vq, uint16_t num)
>  }
>  
>  /* Cleanup from completed inorder transmits. */
> -static void
> +static __rte_always_inline void
>  virtio_xmit_cleanup_inorder(struct virtqueue *vq, uint16_t num)
>  {
>  	uint16_t i, idx = vq->vq_used_cons_idx;
> @@ -2152,6 +2152,21 @@ virtio_xmit_pkts(void *tx_queue, struct rte_mbuf **tx_pkts, uint16_t nb_pkts)
>  	return nb_tx;
>  }
>  
> +static __rte_always_inline int
> +virtio_xmit_try_cleanup_inorder(struct virtqueue *vq, uint16_t need)
> +{
> +	uint16_t nb_used;
> +	struct virtio_hw *hw = vq->hw;
> +
> +	nb_used = VIRTQUEUE_NUSED(vq);
> +	virtio_rmb(hw->weak_barriers);
> +	need = RTE_MIN(need, (int)nb_used);
> +
> +	virtio_xmit_cleanup_inorder(vq, need);
> +
> +	return (need - vq->vq_free_cnt);

It's possible that the `need` has been changed by

	need = RTE_MIN(need, (int)nb_used);

So it can't reflect the actual needs.

Besides, you are passing (nb_inorder_pkts - vq->vq_free_cnt)
as the `need`, here you can't subtract vq->vq_free_cnt to see
whether the needs have been met.

> +}
> +
>  uint16_t
>  virtio_xmit_pkts_inorder(void *tx_queue,
>  			struct rte_mbuf **tx_pkts,
> @@ -2161,8 +2176,9 @@ virtio_xmit_pkts_inorder(void *tx_queue,
>  	struct virtqueue *vq = txvq->vq;
>  	struct virtio_hw *hw = vq->hw;
>  	uint16_t hdr_size = hw->vtnet_hdr_size;
> -	uint16_t nb_used, nb_avail, nb_tx = 0, nb_inorder_pkts = 0;
> +	uint16_t nb_used, nb_tx = 0, nb_inorder_pkts = 0;
>  	struct rte_mbuf *inorder_pkts[nb_pkts];
> +	int need, nb_left;
>  
>  	if (unlikely(hw->started == 0 && tx_pkts != hw->inject_pkts))
>  		return nb_tx;
> @@ -2175,17 +2191,12 @@ virtio_xmit_pkts_inorder(void *tx_queue,
>  	nb_used = VIRTQUEUE_NUSED(vq);
>  
>  	virtio_rmb(hw->weak_barriers);
> -	if (likely(nb_used > vq->vq_nentries - vq->vq_free_thresh))
> -		virtio_xmit_cleanup_inorder(vq, nb_used);
> -
> -	if (unlikely(!vq->vq_free_cnt))
> +	if (likely(nb_used > (vq->vq_nentries - vq->vq_free_thresh)))
>  		virtio_xmit_cleanup_inorder(vq, nb_used);
>  
> -	nb_avail = RTE_MIN(vq->vq_free_cnt, nb_pkts);
> -
> -	for (nb_tx = 0; nb_tx < nb_avail; nb_tx++) {
> +	for (nb_tx = 0; nb_tx < nb_pkts; nb_tx++) {
>  		struct rte_mbuf *txm = tx_pkts[nb_tx];
> -		int slots, need;
> +		int slots;
>  
>  		/* optimize ring usage */
>  		if ((vtpci_with_feature(hw, VIRTIO_F_ANY_LAYOUT) ||
> @@ -2203,6 +2214,22 @@ virtio_xmit_pkts_inorder(void *tx_queue,
>  		}
>  
>  		if (nb_inorder_pkts) {
> +			need = nb_inorder_pkts - vq->vq_free_cnt;
> +
> +

There is no need to add blank lines here.

> +			if (unlikely(need > 0)) {
> +				nb_left = virtio_xmit_try_cleanup_inorder(vq,
> +									need);
> +
> +				if (unlikely(nb_left > 0)) {
> +					PMD_TX_LOG(ERR,
> +						"No free tx descriptors to "
> +						"transmit");
> +					nb_inorder_pkts = vq->vq_free_cnt;

You need to handle nb_tx as well.

> +					break;
> +				}
> +			}
> +
>  			virtqueue_enqueue_xmit_inorder(txvq, inorder_pkts,
>  							nb_inorder_pkts);
>  			nb_inorder_pkts = 0;
> @@ -2211,15 +2238,9 @@ virtio_xmit_pkts_inorder(void *tx_queue,
>  		slots = txm->nb_segs + 1;
>  		need = slots - vq->vq_free_cnt;
>  		if (unlikely(need > 0)) {
> -			nb_used = VIRTQUEUE_NUSED(vq);
> -			virtio_rmb(hw->weak_barriers);
> -			need = RTE_MIN(need, (int)nb_used);
> +			nb_left = virtio_xmit_try_cleanup_inorder(vq, need);
>  
> -			virtio_xmit_cleanup_inorder(vq, need);
> -
> -			need = slots - vq->vq_free_cnt;
> -
> -			if (unlikely(need > 0)) {
> +			if (unlikely(nb_left > 0)) {
>  				PMD_TX_LOG(ERR,
>  					"No free tx descriptors to transmit");
>  				break;
> @@ -2232,9 +2253,23 @@ virtio_xmit_pkts_inorder(void *tx_queue,
>  	}
>  
>  	/* Transmit all inorder packets */
> -	if (nb_inorder_pkts)
> +	if (nb_inorder_pkts) {
> +		need = nb_inorder_pkts - vq->vq_free_cnt;
> +
> +		if (unlikely(need > 0)) {
> +			nb_left = virtio_xmit_try_cleanup_inorder(vq, need);
> +
> +			if (unlikely(nb_left > 0)) {
> +				PMD_TX_LOG(ERR,
> +					"No free tx descriptors to transmit");
> +				nb_inorder_pkts = vq->vq_free_cnt;
> +				nb_tx -= nb_left;
> +			}
> +		}
> +
>  		virtqueue_enqueue_xmit_inorder(txvq, inorder_pkts,
>  						nb_inorder_pkts);
> +	}
>  
>  	txvq->stats.packets += nb_tx;
>  
> -- 
> 2.17.1
>