[dpdk-dev] [PATCH v2 03/16] vhost: add burst enqueue function for packed ring

[Gavin Hu (Arm Technology China)]

Hi Marvin,

Is it possible to vectorize the processing? 
Other comments inline:
/Gavin
> -----Original Message-----
> From: dev <dev-bounces at dpdk.org> On Behalf Of Marvin Liu
> Sent: Friday, September 20, 2019 12:37 AM
> To: maxime.coquelin at redhat.com; tiwei.bie at intel.com;
> zhihong.wang at intel.com
> Cc: dev at dpdk.org; Marvin Liu <yong.liu at intel.com>
> Subject: [dpdk-dev] [PATCH v2 03/16] vhost: add burst enqueue function for
> packed ring
> 
> Burst enqueue function will first check whether descriptors are cache
> aligned. It will also check prerequisites in the beginning. Burst
> enqueue function not support chained mbufs, single packet enqueue
> function will handle it.
> 
> Signed-off-by: Marvin Liu <yong.liu at intel.com>
> 
> diff --git a/lib/librte_vhost/vhost.h b/lib/librte_vhost/vhost.h
> index 5074226f0..67889c80a 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_DESCS_BURST (RTE_CACHE_LINE_SIZE / \
> +			    sizeof(struct vring_packed_desc))
> +
>  #ifdef SUPPORT_GCC_UNROLL_PRAGMA
>  #define PRAGMA_PARAM "GCC unroll 4"
>  #endif
> @@ -57,6 +60,8 @@
>  #define UNROLL_PRAGMA(param) do {} while(0);
>  #endif
> 
> +#define PACKED_BURST_MASK (PACKED_DESCS_BURST - 1)
> +
>  /**
>   * 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 2b5c47145..c664b27c5 100644
> --- a/lib/librte_vhost/virtio_net.c
> +++ b/lib/librte_vhost/virtio_net.c
> @@ -895,6 +895,84 @@ virtio_dev_rx_split(struct virtio_net *dev, struct
> vhost_virtqueue *vq,
>  	return pkt_idx;
>  }
> 
> +static __rte_unused __rte_always_inline int
I remember "__rte_always_inline" should start at the first and separate line, otherwise you will get a style issue. 
/Gavin
> +virtio_dev_rx_burst_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_DESCS_BURST];
> +	struct virtio_net_hdr_mrg_rxbuf *hdrs[PACKED_DESCS_BURST];
> +	uint32_t buf_offset = dev->vhost_hlen;
> +	uint64_t lens[PACKED_DESCS_BURST];
> +
> +	uint16_t i;
> +
> +	if (unlikely(avail_idx & PACKED_BURST_MASK))
> +		return -1;
> +
> +	UNROLL_PRAGMA(PRAGMA_PARAM)
> +	for (i = 0; i < PACKED_DESCS_BURST; 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(PRAGMA_PARAM)
> +	for (i = 0; i < PACKED_DESCS_BURST; i++)
> +		lens[i] = descs[avail_idx + i].len;
Looks like the code is a strong candidate for vectorization. 
> +
> +	UNROLL_PRAGMA(PRAGMA_PARAM)
> +	for (i = 0; i < PACKED_DESCS_BURST; i++) {
> +		if (unlikely(pkts[i]->pkt_len > (lens[i] - buf_offset)))
> +			return -1;
> +	}
> +
> +	UNROLL_PRAGMA(PRAGMA_PARAM)
> +	for (i = 0; i < PACKED_DESCS_BURST; i++)
> +		desc_addrs[i] = vhost_iova_to_vva(dev, vq,
> +						 descs[avail_idx + i].addr,
> +						 &lens[i],
> +						 VHOST_ACCESS_RW);
> +	UNROLL_PRAGMA(PRAGMA_PARAM)
> +	for (i = 0; i < PACKED_DESCS_BURST; i++) {
> +		if (unlikely(lens[i] != descs[avail_idx + i].len))
> +			return -1;
> +	}
> +
> +	UNROLL_PRAGMA(PRAGMA_PARAM)
> +	for (i = 0; i < PACKED_DESCS_BURST; i++) {
> +		rte_prefetch0((void *)(uintptr_t)desc_addrs[i]);
> +		hdrs[i] = (struct virtio_net_hdr_mrg_rxbuf *)desc_addrs[i];
> +		lens[i] = pkts[i]->pkt_len + dev->vhost_hlen;
> +	}
> +
> +	UNROLL_PRAGMA(PRAGMA_PARAM)
> +	for (i = 0; i < PACKED_DESCS_BURST; i++)
> +		virtio_enqueue_offload(pkts[i], &hdrs[i]->hdr);
> +
A store barrier here is missing, last_avail_idx may be observed before the above enqueue completion on weak memory order architectures.
For x86, a compiler barrier is also required. 

> +	vq->last_avail_idx += PACKED_DESCS_BURST;
> +	if (vq->last_avail_idx >= vq->size) {
> +		vq->last_avail_idx -= vq->size;
> +		vq->avail_wrap_counter ^= 1;
> +	}
> +
> +	UNROLL_PRAGMA(PRAGMA_PARAM)
> +	for (i = 0; i < PACKED_DESCS_BURST; 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)
> --
> 2.17.1