Re: [PATCH v2 3/3] net/virtio: improve batching in mergeable path

[Tiwei Bie <tiwei.bie@intel.com>]

On Tue, Dec 11, 2018 at 02:48:04PM +0100, Maxime Coquelin wrote:
> This patch improves both descriptors dequeue and refill,
> by using the same bathing strategy as done in in-order path.
> 
> Signed-off-by: Maxime Coquelin <maxime.coquelin@redhat.com>
> ---
>  drivers/net/virtio/virtio_rxtx.c | 237 ++++++++++++++++---------------
>  1 file changed, 126 insertions(+), 111 deletions(-)
> 
> diff --git a/drivers/net/virtio/virtio_rxtx.c b/drivers/net/virtio/virtio_rxtx.c
> index ebe5c74b5..59bcac2f7 100644
> --- a/drivers/net/virtio/virtio_rxtx.c
> +++ b/drivers/net/virtio/virtio_rxtx.c
> @@ -267,41 +267,42 @@ virtqueue_enqueue_refill_inorder(struct virtqueue *vq,
>  }
>  
>  static inline int
> -virtqueue_enqueue_recv_refill(struct virtqueue *vq, struct rte_mbuf *cookie)
> +virtqueue_enqueue_recv_refill(struct virtqueue *vq, struct rte_mbuf **cookie,
> +				uint16_t num)
>  {
>  	struct vq_desc_extra *dxp;
>  	struct virtio_hw *hw = vq->hw;
> -	struct vring_desc *start_dp;
> -	uint16_t needed = 1;
> -	uint16_t head_idx, idx;
> +	struct vring_desc *start_dp = vq->vq_ring.desc;
> +	uint16_t idx, i;
>  
>  	if (unlikely(vq->vq_free_cnt == 0))
>  		return -ENOSPC;
> -	if (unlikely(vq->vq_free_cnt < needed))
> +	if (unlikely(vq->vq_free_cnt < num))
>  		return -EMSGSIZE;
>  
> -	head_idx = vq->vq_desc_head_idx;
> -	if (unlikely(head_idx >= vq->vq_nentries))
> +	if (unlikely(vq->vq_desc_head_idx >= vq->vq_nentries))
>  		return -EFAULT;
>  
> -	idx = head_idx;
> -	dxp = &vq->vq_descx[idx];
> -	dxp->cookie = (void *)cookie;
> -	dxp->ndescs = needed;
> +	for (i = 0; i < num; i++) {
> +		idx = vq->vq_desc_head_idx;
> +		dxp = &vq->vq_descx[idx];
> +		dxp->cookie = (void *)cookie[i];
> +		dxp->ndescs = 1;
>  
> -	start_dp = vq->vq_ring.desc;
> -	start_dp[idx].addr =
> -		VIRTIO_MBUF_ADDR(cookie, vq) +
> -		RTE_PKTMBUF_HEADROOM - hw->vtnet_hdr_size;
> -	start_dp[idx].len =
> -		cookie->buf_len - RTE_PKTMBUF_HEADROOM + hw->vtnet_hdr_size;
> -	start_dp[idx].flags =  VRING_DESC_F_WRITE;
> -	idx = start_dp[idx].next;
> -	vq->vq_desc_head_idx = idx;
> -	if (vq->vq_desc_head_idx == VQ_RING_DESC_CHAIN_END)
> -		vq->vq_desc_tail_idx = idx;
> -	vq->vq_free_cnt = (uint16_t)(vq->vq_free_cnt - needed);
> -	vq_update_avail_ring(vq, head_idx);
> +		start_dp[idx].addr =
> +			VIRTIO_MBUF_ADDR(cookie[i], vq) +
> +			RTE_PKTMBUF_HEADROOM - hw->vtnet_hdr_size;
> +		start_dp[idx].len =
> +			cookie[i]->buf_len - RTE_PKTMBUF_HEADROOM +
> +			hw->vtnet_hdr_size;
> +		start_dp[idx].flags = VRING_DESC_F_WRITE;
> +		vq->vq_desc_head_idx = start_dp[idx].next;
> +		if (vq->vq_desc_head_idx == VQ_RING_DESC_CHAIN_END)
> +			vq->vq_desc_tail_idx = vq->vq_desc_head_idx;

It's better to break the loop here. Or maybe move
this check out of the loop.

> +		vq_update_avail_ring(vq, idx);
> +	}
> +
> +	vq->vq_free_cnt = (uint16_t)(vq->vq_free_cnt - num);
>  
>  	return 0;
>  }
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