Re: [dpdk-dev] [PATCH v3 03/15] vhost: add batch enqueue function for packed ring

["Mattias Rönnblom" <hofors@lysator.liu.se>]

On 2019-09-25 19:13, Marvin Liu wrote:
> Batch enqueue function will first check whether descriptors are cache
> aligned. It will also check prerequisites in the beginning. Batch
> enqueue function not support chained mbufs, single packet enqueue
> 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 4cba8c5ef..e241436c7 100644
> --- a/lib/librte_vhost/vhost.h
> +++ b/lib/librte_vhost/vhost.h
> @@ -39,6 +39,10 @@
>   
>   #define VHOST_LOG_CACHE_NR 32
>   
> +#define PACKED_BATCH_SIZE (RTE_CACHE_LINE_SIZE / \
> +			    sizeof(struct vring_packed_desc))
> +#define PACKED_BATCH_MASK (PACKED_BATCH_SIZE - 1)
> +
>   #ifdef SUPPORT_GCC_UNROLL_PRAGMA
>   #define UNROLL_PRAGMA_PARAM "GCC unroll 4"
>   #endif
> diff --git a/lib/librte_vhost/virtio_net.c b/lib/librte_vhost/virtio_net.c
> index 520c4c6a8..5e08f7d9b 100644
> --- a/lib/librte_vhost/virtio_net.c
> +++ b/lib/librte_vhost/virtio_net.c
> @@ -883,6 +883,86 @@ virtio_dev_rx_split(struct virtio_net *dev, struct vhost_virtqueue *vq,
>   	return pkt_idx;
>   }
>   
> +static __rte_unused int
> +virtio_dev_rx_batch_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_addrs[PACKED_BATCH_SIZE];
> +	struct virtio_net_hdr_mrg_rxbuf *hdrs[PACKED_BATCH_SIZE];
> +	uint32_t buf_offset = dev->vhost_hlen;
> +	uint64_t lens[PACKED_BATCH_SIZE];
> +	uint16_t i;
> +
> +	if (unlikely(avail_idx & PACKED_BATCH_MASK))
> +		return -1;

Does this really generate better code than just "avail_idx < 
PACKED_BATCH_SIZE"? and+jne vs cmp+jbe.

> +
> +	if (unlikely((avail_idx + PACKED_BATCH_SIZE) > vq->size))
> +		return -1;
> +
> +	UNROLL_PRAGMA(UNROLL_PRAGMA_PARAM)
> +	for (i = 0; i < PACKED_BATCH_SIZE; i++) {
> +		if (unlikely(pkts[i]->next != NULL))
> +			return -1;
> +		if (unlikely(!desc_is_avail(&descs[avail_idx + i],
> +					    wrap_counter)))
> +			return -1;
> +	}
> +
> +	rte_smp_rmb();
> +
> +	UNROLL_PRAGMA(UNROLL_PRAGMA_PARAM)
> +	for (i = 0; i < PACKED_BATCH_SIZE; i++)
> +		lens[i] = descs[avail_idx + i].len;
> +
> +	UNROLL_PRAGMA(UNROLL_PRAGMA_PARAM)
> +	for (i = 0; i < PACKED_BATCH_SIZE; i++) {
> +		if (unlikely(pkts[i]->pkt_len > (lens[i] - buf_offset)))
> +			return -1;
> +	}
> +
> +	UNROLL_PRAGMA(UNROLL_PRAGMA_PARAM)
> +	for (i = 0; i < PACKED_BATCH_SIZE; i++)
> +		desc_addrs[i] = vhost_iova_to_vva(dev, vq,
> +						  descs[avail_idx + i].addr,
> +						  &lens[i],
> +						  VHOST_ACCESS_RW);
> +	UNROLL_PRAGMA(UNROLL_PRAGMA_PARAM)
> +	for (i = 0; i < PACKED_BATCH_SIZE; i++) {
> +		if (unlikely(lens[i] != descs[avail_idx + i].len))
> +			return -1;
> +	}
> +
> +	UNROLL_PRAGMA(UNROLL_PRAGMA_PARAM)
> +	for (i = 0; i < PACKED_BATCH_SIZE; i++) {
> +		rte_prefetch0((void *)(uintptr_t)desc_addrs[i]);
> +		hdrs[i] = (struct virtio_net_hdr_mrg_rxbuf *)
> +					(uintptr_t)desc_addrs[i];
> +		lens[i] = pkts[i]->pkt_len + dev->vhost_hlen;
> +	}
> +
> +	UNROLL_PRAGMA(UNROLL_PRAGMA_PARAM)
> +	for (i = 0; i < PACKED_BATCH_SIZE; i++)
> +		virtio_enqueue_offload(pkts[i], &hdrs[i]->hdr);
> +
> +	vq->last_avail_idx += PACKED_BATCH_SIZE;
> +	if (vq->last_avail_idx >= vq->size) {
> +		vq->last_avail_idx -= vq->size;
> +		vq->avail_wrap_counter ^= 1;
> +	}
> +
> +	UNROLL_PRAGMA(UNROLL_PRAGMA_PARAM)
> +	for (i = 0; i < PACKED_BATCH_SIZE; i++) {
> +		rte_memcpy((void *)(uintptr_t)(desc_addrs[i] + buf_offset),
> +			   rte_pktmbuf_mtod_offset(pkts[i], void *, 0),
> +			   pkts[i]->pkt_len);
> +	}
> +
> +	return 0;
> +}
> +
>   static __rte_unused int16_t
>   virtio_dev_rx_single_packed(struct virtio_net *dev, struct vhost_virtqueue *vq,
>   	struct rte_mbuf *pkt)
>