Re: [dpdk-dev] [PATCH v5 20/24] net/ngbe: support bulk and scatter Rx

[Andrew Rybchenko <andrew.rybchenko@oktetlabs.ru>]

On 6/2/21 12:41 PM, Jiawen Wu wrote:
> Add bulk allocation receive function, and support scattered Rx rely on
> Rx offload.

The patch should advertise Rx scatter offload, not earlier.
Corresponding bits of the patch should be here as well.

> Signed-off-by: Jiawen Wu <jiawenwu@trustnetic.com>
> ---
>   doc/guides/nics/ngbe.rst       |   1 +
>   drivers/net/ngbe/ngbe_ethdev.c |  15 +-
>   drivers/net/ngbe/ngbe_ethdev.h |   8 +
>   drivers/net/ngbe/ngbe_rxtx.c   | 583 +++++++++++++++++++++++++++++++++
>   drivers/net/ngbe/ngbe_rxtx.h   |   2 +
>   5 files changed, 607 insertions(+), 2 deletions(-)
> 
> diff --git a/doc/guides/nics/ngbe.rst b/doc/guides/nics/ngbe.rst
> index 04fa3e90a8..e999e0b580 100644
> --- a/doc/guides/nics/ngbe.rst
> +++ b/doc/guides/nics/ngbe.rst
> @@ -14,6 +14,7 @@ Features
>   - Checksum offload
>   - Jumbo frames
>   - Link state information
> +- Scattered and gather for RX
>   
>   Prerequisites
>   -------------
> diff --git a/drivers/net/ngbe/ngbe_ethdev.c b/drivers/net/ngbe/ngbe_ethdev.c
> index 4dab920caa..260bca0e4f 100644
> --- a/drivers/net/ngbe/ngbe_ethdev.c
> +++ b/drivers/net/ngbe/ngbe_ethdev.c
> @@ -112,8 +112,16 @@ eth_ngbe_dev_init(struct rte_eth_dev *eth_dev, void *init_params __rte_unused)
>   	eth_dev->rx_pkt_burst = &ngbe_recv_pkts;
>   	eth_dev->tx_pkt_burst = &ngbe_xmit_pkts_simple;
>   
> -	if (rte_eal_process_type() != RTE_PROC_PRIMARY)
> +	/*
> +	 * For secondary processes, we don't initialise any further as primary
> +	 * has already done this work. Only check we don't need a different
> +	 * RX and TX function.

RX -> Rx, TX -> Tx

> +	 */
> +	if (rte_eal_process_type() != RTE_PROC_PRIMARY) {
> +		ngbe_set_rx_function(eth_dev);
> +
>   		return 0;
> +	}
>   
>   	rte_eth_copy_pci_info(eth_dev, pci_dev);
>   
> @@ -359,7 +367,10 @@ ngbe_dev_info_get(struct rte_eth_dev *dev, struct rte_eth_dev_info *dev_info)
>   const uint32_t *
>   ngbe_dev_supported_ptypes_get(struct rte_eth_dev *dev)
>   {
> -	if (dev->rx_pkt_burst == ngbe_recv_pkts)
> +	if (dev->rx_pkt_burst == ngbe_recv_pkts ||
> +	    dev->rx_pkt_burst == ngbe_recv_pkts_sc_single_alloc ||
> +	    dev->rx_pkt_burst == ngbe_recv_pkts_sc_bulk_alloc ||
> +	    dev->rx_pkt_burst == ngbe_recv_pkts_bulk_alloc)

I don't understand why 3 flavors of the Rx are added in the single
patch. It looks separate features with separate conditions to use.

>   		return ngbe_get_supported_ptypes();
>   
>   	return NULL;
> diff --git a/drivers/net/ngbe/ngbe_ethdev.h b/drivers/net/ngbe/ngbe_ethdev.h
> index c0f8483eca..1e21db5e25 100644
> --- a/drivers/net/ngbe/ngbe_ethdev.h
> +++ b/drivers/net/ngbe/ngbe_ethdev.h
> @@ -78,6 +78,14 @@ void ngbe_dev_tx_init(struct rte_eth_dev *dev);
>   uint16_t ngbe_recv_pkts(void *rx_queue, struct rte_mbuf **rx_pkts,
>   		uint16_t nb_pkts);
>   
> +uint16_t ngbe_recv_pkts_bulk_alloc(void *rx_queue, struct rte_mbuf **rx_pkts,
> +				    uint16_t nb_pkts);
> +
> +uint16_t ngbe_recv_pkts_sc_single_alloc(void *rx_queue,
> +		struct rte_mbuf **rx_pkts, uint16_t nb_pkts);
> +uint16_t ngbe_recv_pkts_sc_bulk_alloc(void *rx_queue,
> +		struct rte_mbuf **rx_pkts, uint16_t nb_pkts);
> +
>   uint16_t ngbe_xmit_pkts_simple(void *tx_queue, struct rte_mbuf **tx_pkts,
>   		uint16_t nb_pkts);
>   
> diff --git a/drivers/net/ngbe/ngbe_rxtx.c b/drivers/net/ngbe/ngbe_rxtx.c
> index 9462da5b7a..f633718237 100644
> --- a/drivers/net/ngbe/ngbe_rxtx.c
> +++ b/drivers/net/ngbe/ngbe_rxtx.c
> @@ -321,6 +321,257 @@ rx_desc_error_to_pkt_flags(uint32_t rx_status)
>   	return pkt_flags;
>   }
>   
> +/*
> + * LOOK_AHEAD defines how many desc statuses to check beyond the
> + * current descriptor.
> + * It must be a pound define for optimal performance.
> + * Do not change the value of LOOK_AHEAD, as the ngbe_rx_scan_hw_ring
> + * function only works with LOOK_AHEAD=8.
> + */
> +#define LOOK_AHEAD 8
> +#if (LOOK_AHEAD != 8)
> +#error "PMD NGBE: LOOK_AHEAD must be 8\n"
> +#endif
> +static inline int
> +ngbe_rx_scan_hw_ring(struct ngbe_rx_queue *rxq)
> +{
> +	volatile struct ngbe_rx_desc *rxdp;
> +	struct ngbe_rx_entry *rxep;
> +	struct rte_mbuf *mb;
> +	uint16_t pkt_len;
> +	uint64_t pkt_flags;
> +	int nb_dd;
> +	uint32_t s[LOOK_AHEAD];
> +	uint32_t pkt_info[LOOK_AHEAD];
> +	int i, j, nb_rx = 0;
> +	uint32_t status;
> +
> +	/* get references to current descriptor and S/W ring entry */
> +	rxdp = &rxq->rx_ring[rxq->rx_tail];
> +	rxep = &rxq->sw_ring[rxq->rx_tail];
> +
> +	status = rxdp->qw1.lo.status;
> +	/* check to make sure there is at least 1 packet to receive */
> +	if (!(status & rte_cpu_to_le_32(NGBE_RXD_STAT_DD)))
> +		return 0;
> +
> +	/*
> +	 * Scan LOOK_AHEAD descriptors at a time to determine which descriptors
> +	 * reference packets that are ready to be received.
> +	 */
> +	for (i = 0; i < RTE_PMD_NGBE_RX_MAX_BURST;
> +	     i += LOOK_AHEAD, rxdp += LOOK_AHEAD, rxep += LOOK_AHEAD) {
> +		/* Read desc statuses backwards to avoid race condition */
> +		for (j = 0; j < LOOK_AHEAD; j++)
> +			s[j] = rte_le_to_cpu_32(rxdp[j].qw1.lo.status);
> +
> +		rte_atomic_thread_fence(__ATOMIC_ACQUIRE);
> +
> +		/* Compute how many status bits were set */
> +		for (nb_dd = 0; nb_dd < LOOK_AHEAD &&
> +				(s[nb_dd] & NGBE_RXD_STAT_DD); nb_dd++)
> +			;
> +
> +		for (j = 0; j < nb_dd; j++)
> +			pkt_info[j] = rte_le_to_cpu_32(rxdp[j].qw0.dw0);
> +
> +		nb_rx += nb_dd;
> +
> +		/* Translate descriptor info to mbuf format */
> +		for (j = 0; j < nb_dd; ++j) {
> +			mb = rxep[j].mbuf;
> +			pkt_len = rte_le_to_cpu_16(rxdp[j].qw1.hi.len) -
> +				  rxq->crc_len;
> +			mb->data_len = pkt_len;
> +			mb->pkt_len = pkt_len;
> +			mb->vlan_tci = rte_le_to_cpu_16(rxdp[j].qw1.hi.tag);
> +
> +			/* convert descriptor fields to rte mbuf flags */
> +			pkt_flags = rx_desc_status_to_pkt_flags(s[j],
> +					rxq->vlan_flags);
> +			pkt_flags |= rx_desc_error_to_pkt_flags(s[j]);
> +			pkt_flags |=
> +				ngbe_rxd_pkt_info_to_pkt_flags(pkt_info[j]);
> +			mb->ol_flags = pkt_flags;
> +			mb->packet_type =
> +				ngbe_rxd_pkt_info_to_pkt_type(pkt_info[j],
> +				rxq->pkt_type_mask);
> +
> +			if (likely(pkt_flags & PKT_RX_RSS_HASH))
> +				mb->hash.rss =
> +					rte_le_to_cpu_32(rxdp[j].qw0.dw1);
> +		}
> +
> +		/* Move mbuf pointers from the S/W ring to the stage */
> +		for (j = 0; j < LOOK_AHEAD; ++j)
> +			rxq->rx_stage[i + j] = rxep[j].mbuf;
> +
> +		/* stop if all requested packets could not be received */
> +		if (nb_dd != LOOK_AHEAD)
> +			break;
> +	}
> +
> +	/* clear software ring entries so we can cleanup correctly */
> +	for (i = 0; i < nb_rx; ++i)
> +		rxq->sw_ring[rxq->rx_tail + i].mbuf = NULL;
> +
> +	return nb_rx;
> +}
> +
> +static inline int
> +ngbe_rx_alloc_bufs(struct ngbe_rx_queue *rxq, bool reset_mbuf)
> +{
> +	volatile struct ngbe_rx_desc *rxdp;
> +	struct ngbe_rx_entry *rxep;
> +	struct rte_mbuf *mb;
> +	uint16_t alloc_idx;
> +	__le64 dma_addr;
> +	int diag, i;
> +
> +	/* allocate buffers in bulk directly into the S/W ring */
> +	alloc_idx = rxq->rx_free_trigger - (rxq->rx_free_thresh - 1);
> +	rxep = &rxq->sw_ring[alloc_idx];
> +	diag = rte_mempool_get_bulk(rxq->mb_pool, (void *)rxep,
> +				    rxq->rx_free_thresh);
> +	if (unlikely(diag != 0))
> +		return -ENOMEM;
> +
> +	rxdp = &rxq->rx_ring[alloc_idx];
> +	for (i = 0; i < rxq->rx_free_thresh; ++i) {
> +		/* populate the static rte mbuf fields */
> +		mb = rxep[i].mbuf;
> +		if (reset_mbuf)
> +			mb->port = rxq->port_id;
> +
> +		rte_mbuf_refcnt_set(mb, 1);
> +		mb->data_off = RTE_PKTMBUF_HEADROOM;
> +
> +		/* populate the descriptors */
> +		dma_addr = rte_cpu_to_le_64(rte_mbuf_data_iova_default(mb));
> +		NGBE_RXD_HDRADDR(&rxdp[i], 0);
> +		NGBE_RXD_PKTADDR(&rxdp[i], dma_addr);
> +	}
> +
> +	/* update state of internal queue structure */
> +	rxq->rx_free_trigger = rxq->rx_free_trigger + rxq->rx_free_thresh;
> +	if (rxq->rx_free_trigger >= rxq->nb_rx_desc)
> +		rxq->rx_free_trigger = rxq->rx_free_thresh - 1;
> +
> +	/* no errors */
> +	return 0;
> +}
> +
> +static inline uint16_t
> +ngbe_rx_fill_from_stage(struct ngbe_rx_queue *rxq, struct rte_mbuf **rx_pkts,
> +			 uint16_t nb_pkts)
> +{
> +	struct rte_mbuf **stage = &rxq->rx_stage[rxq->rx_next_avail];
> +	int i;
> +
> +	/* how many packets are ready to return? */
> +	nb_pkts = (uint16_t)RTE_MIN(nb_pkts, rxq->rx_nb_avail);
> +
> +	/* copy mbuf pointers to the application's packet list */
> +	for (i = 0; i < nb_pkts; ++i)
> +		rx_pkts[i] = stage[i];
> +
> +	/* update internal queue state */
> +	rxq->rx_nb_avail = (uint16_t)(rxq->rx_nb_avail - nb_pkts);
> +	rxq->rx_next_avail = (uint16_t)(rxq->rx_next_avail + nb_pkts);
> +
> +	return nb_pkts;
> +}
> +
> +static inline uint16_t
> +ngbe_rx_recv_pkts(void *rx_queue, struct rte_mbuf **rx_pkts,
> +	     uint16_t nb_pkts)
> +{
> +	struct ngbe_rx_queue *rxq = (struct ngbe_rx_queue *)rx_queue;
> +	struct rte_eth_dev *dev = &rte_eth_devices[rxq->port_id];
> +	uint16_t nb_rx = 0;
> +
> +	/* Any previously recv'd pkts will be returned from the Rx stage */
> +	if (rxq->rx_nb_avail)
> +		return ngbe_rx_fill_from_stage(rxq, rx_pkts, nb_pkts);
> +
> +	/* Scan the H/W ring for packets to receive */
> +	nb_rx = (uint16_t)ngbe_rx_scan_hw_ring(rxq);
> +
> +	/* update internal queue state */
> +	rxq->rx_next_avail = 0;
> +	rxq->rx_nb_avail = nb_rx;
> +	rxq->rx_tail = (uint16_t)(rxq->rx_tail + nb_rx);
> +
> +	/* if required, allocate new buffers to replenish descriptors */
> +	if (rxq->rx_tail > rxq->rx_free_trigger) {
> +		uint16_t cur_free_trigger = rxq->rx_free_trigger;
> +
> +		if (ngbe_rx_alloc_bufs(rxq, true) != 0) {
> +			int i, j;
> +
> +			PMD_RX_LOG(DEBUG, "RX mbuf alloc failed port_id=%u "
> +				   "queue_id=%u", (uint16_t)rxq->port_id,
> +				   (uint16_t)rxq->queue_id);
> +
> +			dev->data->rx_mbuf_alloc_failed +=
> +				rxq->rx_free_thresh;
> +
> +			/*
> +			 * Need to rewind any previous receives if we cannot
> +			 * allocate new buffers to replenish the old ones.
> +			 */
> +			rxq->rx_nb_avail = 0;
> +			rxq->rx_tail = (uint16_t)(rxq->rx_tail - nb_rx);
> +			for (i = 0, j = rxq->rx_tail; i < nb_rx; ++i, ++j)
> +				rxq->sw_ring[j].mbuf = rxq->rx_stage[i];
> +
> +			return 0;
> +		}
> +
> +		/* update tail pointer */
> +		rte_wmb();
> +		ngbe_set32_relaxed(rxq->rdt_reg_addr, cur_free_trigger);
> +	}
> +
> +	if (rxq->rx_tail >= rxq->nb_rx_desc)
> +		rxq->rx_tail = 0;
> +
> +	/* received any packets this loop? */
> +	if (rxq->rx_nb_avail)
> +		return ngbe_rx_fill_from_stage(rxq, rx_pkts, nb_pkts);
> +
> +	return 0;
> +}
> +
> +/* split requests into chunks of size RTE_PMD_NGBE_RX_MAX_BURST */
> +uint16_t
> +ngbe_recv_pkts_bulk_alloc(void *rx_queue, struct rte_mbuf **rx_pkts,
> +			   uint16_t nb_pkts)
> +{
> +	uint16_t nb_rx;
> +
> +	if (unlikely(nb_pkts == 0))
> +		return 0;
> +
> +	if (likely(nb_pkts <= RTE_PMD_NGBE_RX_MAX_BURST))
> +		return ngbe_rx_recv_pkts(rx_queue, rx_pkts, nb_pkts);
> +
> +	/* request is relatively large, chunk it up */
> +	nb_rx = 0;
> +	while (nb_pkts) {
> +		uint16_t ret, n;
> +
> +		n = (uint16_t)RTE_MIN(nb_pkts, RTE_PMD_NGBE_RX_MAX_BURST);
> +		ret = ngbe_rx_recv_pkts(rx_queue, &rx_pkts[nb_rx], n);
> +		nb_rx = (uint16_t)(nb_rx + ret);
> +		nb_pkts = (uint16_t)(nb_pkts - ret);
> +		if (ret < n)
> +			break;
> +	}
> +
> +	return nb_rx;
> +}
> +
>   uint16_t
>   ngbe_recv_pkts(void *rx_queue, struct rte_mbuf **rx_pkts,
>   		uint16_t nb_pkts)
> @@ -501,6 +752,288 @@ ngbe_recv_pkts(void *rx_queue, struct rte_mbuf **rx_pkts,
>   	return nb_rx;
>   }
>   
> +/**
> + * ngbe_fill_cluster_head_buf - fill the first mbuf of the returned packet
> + *
> + * Fill the following info in the HEAD buffer of the Rx cluster:
> + *    - RX port identifier
> + *    - hardware offload data, if any:
> + *      - RSS flag & hash
> + *      - IP checksum flag
> + *      - VLAN TCI, if any
> + *      - error flags
> + * @head HEAD of the packet cluster
> + * @desc HW descriptor to get data from
> + * @rxq Pointer to the Rx queue
> + */
> +static inline void
> +ngbe_fill_cluster_head_buf(struct rte_mbuf *head, struct ngbe_rx_desc *desc,
> +		struct ngbe_rx_queue *rxq, uint32_t staterr)
> +{
> +	uint32_t pkt_info;
> +	uint64_t pkt_flags;
> +
> +	head->port = rxq->port_id;
> +
> +	/* The vlan_tci field is only valid when PKT_RX_VLAN is
> +	 * set in the pkt_flags field.
> +	 */
> +	head->vlan_tci = rte_le_to_cpu_16(desc->qw1.hi.tag);
> +	pkt_info = rte_le_to_cpu_32(desc->qw0.dw0);
> +	pkt_flags = rx_desc_status_to_pkt_flags(staterr, rxq->vlan_flags);
> +	pkt_flags |= rx_desc_error_to_pkt_flags(staterr);
> +	pkt_flags |= ngbe_rxd_pkt_info_to_pkt_flags(pkt_info);
> +	head->ol_flags = pkt_flags;
> +	head->packet_type = ngbe_rxd_pkt_info_to_pkt_type(pkt_info,
> +						rxq->pkt_type_mask);
> +
> +	if (likely(pkt_flags & PKT_RX_RSS_HASH))
> +		head->hash.rss = rte_le_to_cpu_32(desc->qw0.dw1);
> +}
> +
> +/**
> + * ngbe_recv_pkts_sc - receive handler for scatter case.
> + *
> + * @rx_queue Rx queue handle
> + * @rx_pkts table of received packets
> + * @nb_pkts size of rx_pkts table
> + * @bulk_alloc if TRUE bulk allocation is used for a HW ring refilling
> + *
> + * Returns the number of received packets/clusters (according to the "bulk
> + * receive" interface).
> + */
> +static inline uint16_t
> +ngbe_recv_pkts_sc(void *rx_queue, struct rte_mbuf **rx_pkts, uint16_t nb_pkts,
> +		    bool bulk_alloc)
> +{
> +	struct ngbe_rx_queue *rxq = rx_queue;
> +	struct rte_eth_dev *dev = &rte_eth_devices[rxq->port_id];
> +	volatile struct ngbe_rx_desc *rx_ring = rxq->rx_ring;
> +	struct ngbe_rx_entry *sw_ring = rxq->sw_ring;
> +	struct ngbe_scattered_rx_entry *sw_sc_ring = rxq->sw_sc_ring;
> +	uint16_t rx_id = rxq->rx_tail;
> +	uint16_t nb_rx = 0;
> +	uint16_t nb_hold = rxq->nb_rx_hold;
> +	uint16_t prev_id = rxq->rx_tail;
> +
> +	while (nb_rx < nb_pkts) {
> +		bool eop;
> +		struct ngbe_rx_entry *rxe;
> +		struct ngbe_scattered_rx_entry *sc_entry;
> +		struct ngbe_scattered_rx_entry *next_sc_entry = NULL;
> +		struct ngbe_rx_entry *next_rxe = NULL;
> +		struct rte_mbuf *first_seg;
> +		struct rte_mbuf *rxm;
> +		struct rte_mbuf *nmb = NULL;
> +		struct ngbe_rx_desc rxd;
> +		uint16_t data_len;
> +		uint16_t next_id;
> +		volatile struct ngbe_rx_desc *rxdp;
> +		uint32_t staterr;
> +
> +next_desc:
> +		rxdp = &rx_ring[rx_id];
> +		staterr = rte_le_to_cpu_32(rxdp->qw1.lo.status);
> +
> +		if (!(staterr & NGBE_RXD_STAT_DD))
> +			break;
> +
> +		rxd = *rxdp;
> +
> +		PMD_RX_LOG(DEBUG, "port_id=%u queue_id=%u rx_id=%u "
> +				  "staterr=0x%x data_len=%u",
> +			   rxq->port_id, rxq->queue_id, rx_id, staterr,
> +			   rte_le_to_cpu_16(rxd.qw1.hi.len));
> +
> +		if (!bulk_alloc) {
> +			nmb = rte_mbuf_raw_alloc(rxq->mb_pool);
> +			if (nmb == NULL) {
> +				PMD_RX_LOG(DEBUG, "RX mbuf alloc failed "
> +						  "port_id=%u queue_id=%u",
> +					   rxq->port_id, rxq->queue_id);
> +
> +				dev->data->rx_mbuf_alloc_failed++;
> +				break;
> +			}
> +		} else if (nb_hold > rxq->rx_free_thresh) {
> +			uint16_t next_rdt = rxq->rx_free_trigger;
> +
> +			if (!ngbe_rx_alloc_bufs(rxq, false)) {
> +				rte_wmb();
> +				ngbe_set32_relaxed(rxq->rdt_reg_addr,
> +							    next_rdt);
> +				nb_hold -= rxq->rx_free_thresh;
> +			} else {
> +				PMD_RX_LOG(DEBUG, "RX bulk alloc failed "
> +						  "port_id=%u queue_id=%u",
> +					   rxq->port_id, rxq->queue_id);
> +
> +				dev->data->rx_mbuf_alloc_failed++;
> +				break;
> +			}
> +		}
> +
> +		nb_hold++;
> +		rxe = &sw_ring[rx_id];
> +		eop = staterr & NGBE_RXD_STAT_EOP;
> +
> +		next_id = rx_id + 1;
> +		if (next_id == rxq->nb_rx_desc)
> +			next_id = 0;
> +
> +		/* Prefetch next mbuf while processing current one. */
> +		rte_ngbe_prefetch(sw_ring[next_id].mbuf);
> +
> +		/*
> +		 * When next RX descriptor is on a cache-line boundary,
> +		 * prefetch the next 4 RX descriptors and the next 4 pointers
> +		 * to mbufs.
> +		 */
> +		if ((next_id & 0x3) == 0) {
> +			rte_ngbe_prefetch(&rx_ring[next_id]);
> +			rte_ngbe_prefetch(&sw_ring[next_id]);
> +		}
> +
> +		rxm = rxe->mbuf;
> +
> +		if (!bulk_alloc) {
> +			__le64 dma =
> +			  rte_cpu_to_le_64(rte_mbuf_data_iova_default(nmb));
> +			/*
> +			 * Update RX descriptor with the physical address of the
> +			 * new data buffer of the new allocated mbuf.
> +			 */
> +			rxe->mbuf = nmb;
> +
> +			rxm->data_off = RTE_PKTMBUF_HEADROOM;
> +			NGBE_RXD_HDRADDR(rxdp, 0);
> +			NGBE_RXD_PKTADDR(rxdp, dma);
> +		} else {
> +			rxe->mbuf = NULL;
> +		}
> +
> +		/*
> +		 * Set data length & data buffer address of mbuf.
> +		 */
> +		data_len = rte_le_to_cpu_16(rxd.qw1.hi.len);
> +		rxm->data_len = data_len;
> +
> +		if (!eop) {
> +			uint16_t nextp_id;
> +
> +			nextp_id = next_id;
> +			next_sc_entry = &sw_sc_ring[nextp_id];
> +			next_rxe = &sw_ring[nextp_id];
> +			rte_ngbe_prefetch(next_rxe);
> +		}
> +
> +		sc_entry = &sw_sc_ring[rx_id];
> +		first_seg = sc_entry->fbuf;
> +		sc_entry->fbuf = NULL;
> +
> +		/*
> +		 * If this is the first buffer of the received packet,
> +		 * set the pointer to the first mbuf of the packet and
> +		 * initialize its context.
> +		 * Otherwise, update the total length and the number of segments
> +		 * of the current scattered packet, and update the pointer to
> +		 * the last mbuf of the current packet.
> +		 */
> +		if (first_seg == NULL) {
> +			first_seg = rxm;
> +			first_seg->pkt_len = data_len;
> +			first_seg->nb_segs = 1;
> +		} else {
> +			first_seg->pkt_len += data_len;
> +			first_seg->nb_segs++;
> +		}
> +
> +		prev_id = rx_id;
> +		rx_id = next_id;
> +
> +		/*
> +		 * If this is not the last buffer of the received packet, update
> +		 * the pointer to the first mbuf at the NEXTP entry in the
> +		 * sw_sc_ring and continue to parse the RX ring.

RX -> Rx

> +		 */
> +		if (!eop && next_rxe) {
> +			rxm->next = next_rxe->mbuf;
> +			next_sc_entry->fbuf = first_seg;
> +			goto next_desc;
> +		}
> +
> +		/* Initialize the first mbuf of the returned packet */
> +		ngbe_fill_cluster_head_buf(first_seg, &rxd, rxq, staterr);
> +
> +		/* Deal with the case, when HW CRC srip is disabled. */
> +		first_seg->pkt_len -= rxq->crc_len;
> +		if (unlikely(rxm->data_len <= rxq->crc_len)) {
> +			struct rte_mbuf *lp;
> +
> +			for (lp = first_seg; lp->next != rxm; lp = lp->next)
> +				;
> +
> +			first_seg->nb_segs--;
> +			lp->data_len -= rxq->crc_len - rxm->data_len;
> +			lp->next = NULL;
> +			rte_pktmbuf_free_seg(rxm);
> +		} else {
> +			rxm->data_len -= rxq->crc_len;
> +		}
> +
> +		/* Prefetch data of first segment, if configured to do so. */
> +		rte_packet_prefetch((char *)first_seg->buf_addr +
> +			first_seg->data_off);
> +
> +		/*
> +		 * Store the mbuf address into the next entry of the array
> +		 * of returned packets.
> +		 */
> +		rx_pkts[nb_rx++] = first_seg;
> +	}
> +
> +	/*
> +	 * Record index of the next RX descriptor to probe.
> +	 */
> +	rxq->rx_tail = rx_id;
> +
> +	/*
> +	 * If the number of free RX descriptors is greater than the RX free

RX -> Rx twice

> +	 * threshold of the queue, advance the Receive Descriptor Tail (RDT)
> +	 * register.
> +	 * Update the RDT with the value of the last processed RX descriptor
> +	 * minus 1, to guarantee that the RDT register is never equal to the
> +	 * RDH register, which creates a "full" ring situation from the
> +	 * hardware point of view...
> +	 */
> +	if (!bulk_alloc && nb_hold > rxq->rx_free_thresh) {
> +		PMD_RX_LOG(DEBUG, "port_id=%u queue_id=%u rx_tail=%u "
> +			   "nb_hold=%u nb_rx=%u",
> +			   rxq->port_id, rxq->queue_id, rx_id, nb_hold, nb_rx);
> +
> +		rte_wmb();
> +		ngbe_set32_relaxed(rxq->rdt_reg_addr, prev_id);
> +		nb_hold = 0;
> +	}
> +
> +	rxq->nb_rx_hold = nb_hold;
> +	return nb_rx;
> +}
> +
> +uint16_t
> +ngbe_recv_pkts_sc_single_alloc(void *rx_queue, struct rte_mbuf **rx_pkts,
> +				 uint16_t nb_pkts)
> +{
> +	return ngbe_recv_pkts_sc(rx_queue, rx_pkts, nb_pkts, false);
> +}
> +
> +uint16_t
> +ngbe_recv_pkts_sc_bulk_alloc(void *rx_queue, struct rte_mbuf **rx_pkts,
> +			       uint16_t nb_pkts)
> +{
> +	return ngbe_recv_pkts_sc(rx_queue, rx_pkts, nb_pkts, true);
> +}
> +
>   /*********************************************************************
>    *
>    *  Queue management functions
> @@ -1064,6 +1597,54 @@ ngbe_dev_rx_queue_setup(struct rte_eth_dev *dev,
>   	return 0;
>   }
>   
> +void __rte_cold
> +ngbe_set_rx_function(struct rte_eth_dev *dev)
> +{
> +	struct ngbe_adapter *adapter = NGBE_DEV_ADAPTER(dev);
> +
> +	if (dev->data->scattered_rx) {
> +		/*
> +		 * Set the scattered callback: there are bulk and
> +		 * single allocation versions.
> +		 */
> +		if (adapter->rx_bulk_alloc_allowed) {
> +			PMD_INIT_LOG(DEBUG, "Using a Scattered with bulk "
> +					   "allocation callback (port=%d).",
> +				     dev->data->port_id);
> +			dev->rx_pkt_burst = ngbe_recv_pkts_sc_bulk_alloc;
> +		} else {
> +			PMD_INIT_LOG(DEBUG, "Using Regular (non-vector, "
> +					    "single allocation) "
> +					    "Scattered Rx callback "
> +					    "(port=%d).",
> +				     dev->data->port_id);
> +
> +			dev->rx_pkt_burst = ngbe_recv_pkts_sc_single_alloc;
> +		}
> +	/*
> +	 * Below we set "simple" callbacks according to port/queues parameters.
> +	 * If parameters allow we are going to choose between the following
> +	 * callbacks:
> +	 *    - Bulk Allocation
> +	 *    - Single buffer allocation (the simplest one)
> +	 */
> +	} else if (adapter->rx_bulk_alloc_allowed) {
> +		PMD_INIT_LOG(DEBUG, "Rx Burst Bulk Alloc Preconditions are "
> +				    "satisfied. Rx Burst Bulk Alloc function "
> +				    "will be used on port=%d.",
> +			     dev->data->port_id);
> +
> +		dev->rx_pkt_burst = ngbe_recv_pkts_bulk_alloc;
> +	} else {
> +		PMD_INIT_LOG(DEBUG, "Rx Burst Bulk Alloc Preconditions are not "
> +				    "satisfied, or Scattered Rx is requested "
> +				    "(port=%d).",
> +			     dev->data->port_id);
> +
> +		dev->rx_pkt_burst = ngbe_recv_pkts;
> +	}
> +}
> +
>   /*
>    * Initializes Receive Unit.
>    */
> @@ -1211,6 +1792,8 @@ ngbe_dev_rx_init(struct rte_eth_dev *dev)
>   		wr32(hw, NGBE_SECRXCTL, rdrxctl);
>   	}
>   
> +	ngbe_set_rx_function(dev);
> +
>   	return 0;
>   }
>   
> diff --git a/drivers/net/ngbe/ngbe_rxtx.h b/drivers/net/ngbe/ngbe_rxtx.h
> index d6b9127cb4..4b8596b24a 100644
> --- a/drivers/net/ngbe/ngbe_rxtx.h
> +++ b/drivers/net/ngbe/ngbe_rxtx.h
> @@ -298,6 +298,8 @@ struct ngbe_txq_ops {
>   	void (*reset)(struct ngbe_tx_queue *txq);
>   };
>   
> +void ngbe_set_rx_function(struct rte_eth_dev *dev);
> +
>   uint64_t ngbe_get_tx_port_offloads(struct rte_eth_dev *dev);
>   uint64_t ngbe_get_rx_queue_offloads(struct rte_eth_dev *dev);
>   uint64_t ngbe_get_rx_port_offloads(struct rte_eth_dev *dev);
>