Re: [dpdk-dev] [RFC PATCH 02/13] add vhost packed ring fast enqueue function

[Jason Wang <jasowang@redhat.com>]

On 2019/7/9 上午1:13, Marvin Liu wrote:
> In fast enqueue function, will first check whether descriptors are
> cache aligned. Fast enqueue function will check prerequisites in the
> beginning. Fast enqueue function do not support chained mbufs, normal
> function will handle that.
>
> Signed-off-by: Marvin Liu<yong.liu@intel.com>
>
> diff --git a/lib/librte_vhost/vhost.h b/lib/librte_vhost/vhost.h
> index 884befa85..f24026acd 100644
> --- a/lib/librte_vhost/vhost.h
> +++ b/lib/librte_vhost/vhost.h
> @@ -39,6 +39,8 @@
>   
>   #define VHOST_LOG_CACHE_NR 32
>   
> +/* Used in fast packed ring functions */
> +#define PACKED_DESC_PER_CACHELINE (RTE_CACHE_LINE_SIZE / sizeof(struct vring_packed_desc))
>   /**
>    * Structure contains buffer address, length and descriptor index
>    * from vring to do scatter RX.
> diff --git a/lib/librte_vhost/virtio_net.c b/lib/librte_vhost/virtio_net.c
> index 003aec1d4..b877510da 100644
> --- a/lib/librte_vhost/virtio_net.c
> +++ b/lib/librte_vhost/virtio_net.c
> @@ -897,6 +897,115 @@ virtio_dev_rx_split(struct virtio_net *dev, struct vhost_virtqueue *vq,
>   	return pkt_idx;
>   }
>   
> +static __rte_always_inline uint16_t
> +virtio_dev_rx_fast_packed(struct virtio_net *dev, struct vhost_virtqueue *vq,
> +		struct rte_mbuf **pkts)
> +{
> +	bool wrap_counter = vq->avail_wrap_counter;
> +	struct vring_packed_desc *descs = vq->desc_packed;
> +	uint16_t avail_idx = vq->last_avail_idx;
> +	uint64_t desc_addr, desc_addr1, desc_addr2, desc_addr3, len, len1,
> +		len2, len3;
> +	struct virtio_net_hdr_mrg_rxbuf *hdr, *hdr1, *hdr2, *hdr3;
> +	uint32_t buf_offset = dev->vhost_hlen;
> +
> +	if (unlikely(avail_idx & 0x3))
> +		return -1;
> +
> +	if (unlikely(avail_idx < (vq->size - PACKED_DESC_PER_CACHELINE)))
> +		rte_prefetch0((void *)(uintptr_t)&descs[avail_idx +
> +			PACKED_DESC_PER_CACHELINE]);
> +	else
> +		rte_prefetch0((void *)(uintptr_t)&descs[0]);
> +
> +	if (unlikely((pkts[0]->next != NULL) |
> +		(pkts[1]->next != NULL) |
> +		(pkts[2]->next != NULL) |
> +		(pkts[3]->next != NULL)))
> +		return -1;
> +
> +	if (unlikely(!desc_is_avail(&descs[avail_idx], wrap_counter)) |
> +		unlikely(!desc_is_avail(&descs[avail_idx + 1], wrap_counter)) |
> +		unlikely(!desc_is_avail(&descs[avail_idx + 2], wrap_counter)) |
> +		unlikely(!desc_is_avail(&descs[avail_idx + 3], wrap_counter)))
> +		return 1;
> +
> +	rte_smp_rmb();
> +
> +	len = descs[avail_idx].len;
> +	len1 = descs[avail_idx + 1].len;
> +	len2 = descs[avail_idx + 2].len;
> +	len3 = descs[avail_idx + 3].len;
> +
> +	if (unlikely((pkts[0]->pkt_len > (len - buf_offset)) |
> +		(pkts[1]->pkt_len > (len1 - buf_offset)) |
> +		(pkts[2]->pkt_len > (len2 - buf_offset)) |
> +		(pkts[3]->pkt_len > (len3 - buf_offset))))
> +		return -1;
> +
> +	desc_addr = vhost_iova_to_vva(dev, vq,
> +			descs[avail_idx].addr,
> +			&len,
> +			VHOST_ACCESS_RW);
> +
> +	desc_addr1 = vhost_iova_to_vva(dev, vq,
> +			descs[avail_idx + 1].addr,
> +			&len1,
> +			VHOST_ACCESS_RW);
> +
> +	desc_addr2 = vhost_iova_to_vva(dev, vq,
> +			descs[avail_idx + 2].addr,
> +			&len2,
> +			VHOST_ACCESS_RW);
> +
> +	desc_addr3 = vhost_iova_to_vva(dev, vq,
> +			descs[avail_idx + 3].addr,
> +			&len3,
> +			VHOST_ACCESS_RW);


How can you guarantee that len3 is zero after this?

Thanks