Re: [dpdk-dev] [PATCH v6 06/13] vhost: add packed ring batch dequeue

[Maxime Coquelin <maxime.coquelin@redhat.com>]

On 10/15/19 6:07 PM, Marvin Liu wrote:
> Add batch dequeue function like enqueue function for packed ring, batch
> dequeue function will not support chained descritpors, single packet
> dequeue function will handle it.
> 
> Signed-off-by: Marvin Liu <yong.liu@intel.com>
> 
> diff --git a/lib/librte_vhost/vhost.h b/lib/librte_vhost/vhost.h
> index 18d01cb19..96bf763b1 100644
> --- a/lib/librte_vhost/vhost.h
> +++ b/lib/librte_vhost/vhost.h
> @@ -39,6 +39,9 @@
>  
>  #define VHOST_LOG_CACHE_NR 32
>  
> +#define PACKED_DESC_SINGLE_DEQUEUE_FLAG (VRING_DESC_F_NEXT | \
> +					 VRING_DESC_F_INDIRECT)
> +
>  #define PACKED_BATCH_SIZE (RTE_CACHE_LINE_SIZE / \
>  			    sizeof(struct vring_packed_desc))
>  #define PACKED_BATCH_MASK (PACKED_BATCH_SIZE - 1)
> diff --git a/lib/librte_vhost/virtio_net.c b/lib/librte_vhost/virtio_net.c
> index e1b06c1ce..274a28f99 100644
> --- a/lib/librte_vhost/virtio_net.c
> +++ b/lib/librte_vhost/virtio_net.c
> @@ -1551,6 +1551,113 @@ virtio_dev_tx_split(struct virtio_net *dev, struct vhost_virtqueue *vq,
>  	return i;
>  }
>  
> +static __rte_always_inline int
> +vhost_reserve_avail_batch_packed(struct virtio_net *dev,
> +				 struct vhost_virtqueue *vq,
> +				 struct rte_mempool *mbuf_pool,
> +				 struct rte_mbuf **pkts,
> +				 uint16_t avail_idx,
> +				 uintptr_t *desc_addrs,
> +				 uint16_t *ids)
> +{
> +	bool wrap = vq->avail_wrap_counter;
> +	struct vring_packed_desc *descs = vq->desc_packed;
> +	struct virtio_net_hdr *hdr;
> +	uint64_t lens[PACKED_BATCH_SIZE];
> +	uint64_t buf_lens[PACKED_BATCH_SIZE];
> +	uint32_t buf_offset = dev->vhost_hlen;
> +	uint16_t flags, i;
> +
> +	if (unlikely(avail_idx & PACKED_BATCH_MASK))
> +		return -1;
> +	if (unlikely((avail_idx + PACKED_BATCH_SIZE) > vq->size))
> +		return -1;
> +
> +	for_each_try_unroll(i, 0, PACKED_BATCH_SIZE) {
> +		flags = descs[avail_idx + i].flags;
> +		if (unlikely((wrap != !!(flags & VRING_DESC_F_AVAIL)) ||
> +			     (wrap == !!(flags & VRING_DESC_F_USED))  ||
> +			     (flags & PACKED_DESC_SINGLE_DEQUEUE_FLAG)))
> +			return -1;
> +	}
> +
> +	rte_smp_rmb();
> +
> +	for_each_try_unroll(i, 0, PACKED_BATCH_SIZE)
> +		lens[i] = descs[avail_idx + i].len;
> +
> +	for_each_try_unroll(i, 0, PACKED_BATCH_SIZE) {
> +		desc_addrs[i] = vhost_iova_to_vva(dev, vq,
> +						  descs[avail_idx + i].addr,
> +						  &lens[i], VHOST_ACCESS_RW);
> +	}
> +
> +	for_each_try_unroll(i, 0, PACKED_BATCH_SIZE) {
> +		if (unlikely((lens[i] != descs[avail_idx + i].len)))
> +			return -1;
> +	}
> +
> +	if (rte_pktmbuf_alloc_bulk(mbuf_pool, pkts, PACKED_BATCH_SIZE))
> +		return -1;
> +
> +	for_each_try_unroll(i, 0, PACKED_BATCH_SIZE)
> +		buf_lens[i] = pkts[i]->buf_len - pkts[i]->data_off;
> +
> +	for_each_try_unroll(i, 0, PACKED_BATCH_SIZE) {
> +		if (unlikely(buf_lens[i] < (lens[i] - buf_offset)))
> +			goto free_buf;
> +	}
> +
> +	for_each_try_unroll(i, 0, PACKED_BATCH_SIZE) {
> +		pkts[i]->pkt_len = descs[avail_idx + i].len - buf_offset;
> +		pkts[i]->data_len = pkts[i]->pkt_len;
> +		ids[i] = descs[avail_idx + i].id;
> +	}
> +
> +	if (virtio_net_with_host_offload(dev)) {
> +		for_each_try_unroll(i, 0, PACKED_BATCH_SIZE) {
> +			hdr = (struct virtio_net_hdr *)(desc_addrs[i]);
> +			vhost_dequeue_offload(hdr, pkts[i]);
> +		}
> +	}
> +
> +	return 0;
> +
> +free_buf:
> +	for (i = 0; i < PACKED_BATCH_SIZE; i++)
> +		rte_pktmbuf_free(pkts[i]);
> +
> +	return -1;
> +}
> +
> +static __rte_unused int
> +virtio_dev_tx_batch_packed(struct virtio_net *dev,
> +			   struct vhost_virtqueue *vq,
> +			   struct rte_mempool *mbuf_pool,
> +			   struct rte_mbuf **pkts)
> +{
> +	uint16_t avail_idx = vq->last_avail_idx;
> +	uint32_t buf_offset = dev->vhost_hlen;
> +	uintptr_t desc_addrs[PACKED_BATCH_SIZE];
> +	uint16_t ids[PACKED_BATCH_SIZE];
> +	uint16_t i;
> +
> +	if (vhost_reserve_avail_batch_packed(dev, vq, mbuf_pool, pkts,
> +					     avail_idx, desc_addrs, ids))
> +		return -1;
> +
> +	for_each_try_unroll(i, 0, PACKED_BATCH_SIZE) {
> +		rte_prefetch0((void *)(uintptr_t)desc_addrs[i]);

Wouldn't we have better performance with a dedicated unroll loop for the
prefetches, so that desc_addrs[i+1] is being prefetched while the
desc_addr[i] memcpy is done?

> +		rte_memcpy(rte_pktmbuf_mtod_offset(pkts[i], void *, 0),
> +			   (void *)(uintptr_t)(desc_addrs[i] + buf_offset),
> +			   pkts[i]->pkt_len);
> +	}
> +
> +	vq_inc_last_avail_packed(vq, PACKED_BATCH_SIZE);
> +
> +	return 0;
> +}
> +
>  static __rte_always_inline int
>  vhost_dequeue_single_packed(struct virtio_net *dev,
>  			    struct vhost_virtqueue *vq,
>