Re: [dpdk-dev] [PATCH v8 1/6] ethdev: introduce Rx buffer split

[Andrew Rybchenko <arybchenko@solarflare.com>]

On 10/16/20 11:51 AM, Andrew Rybchenko wrote:
> On 10/16/20 10:48 AM, Viacheslav Ovsiienko wrote:
>> The DPDK datapath in the transmit direction is very flexible.
>> An application can build the multi-segment packet and manages
>> almost all data aspects - the memory pools where segments
>> are allocated from, the segment lengths, the memory attributes
>> like external buffers, registered for DMA, etc.
>>
>> In the receiving direction, the datapath is much less flexible,
>> an application can only specify the memory pool to configure the
>> receiving queue and nothing more. In order to extend receiving
>> datapath capabilities it is proposed to add the way to provide
>> extended information how to split the packets being received.
>>
>> The new offload flag RTE_ETH_RX_OFFLOAD_BUFFER_SPLIT in device
>> capabilities is introduced to present the way for PMD to report to
>> application about supporting Rx packet split to configurable
>> segments. Prior invoking the rte_eth_rx_queue_setup() routine
>> application should check RTE_ETH_RX_OFFLOAD_BUFFER_SPLIT flag.
>>
>> The following structure is introduced to specify the Rx packet
>> segment for RTE_ETH_RX_OFFLOAD_BUFFER_SPLIT offload:
>>
>> struct rte_eth_rxseg_split {
>>
>>     struct rte_mempool *mp; /* memory pools to allocate segment from */
>>     uint16_t length; /* segment maximal data length,
>> 		       	configures "split point" */
>>     uint16_t offset; /* data offset from beginning
>> 		       	of mbuf data buffer */
>>     uint32_t reserved; /* reserved field */
>> };
>>
>> The segment descriptions are added to the rte_eth_rxconf structure:
>>    rx_seg - pointer the array of segment descriptions, each element
>>              describes the memory pool, maximal data length, initial
>>              data offset from the beginning of data buffer in mbuf.
>> 	     This array allows to specify the different settings for
>> 	     each segment in individual fashion.
>>    rx_nseg - number of elements in the array
>>
>> If the extended segment descriptions is provided with these new
>> fields the mp parameter of the rte_eth_rx_queue_setup must be
>> specified as NULL to avoid ambiguity.
>>
>> There are two options to specify Rx buffer configuration:
>> - mp is not NULL, rx_conf.rx_seg is NULL, rx_conf.rx_nseg is zero,
>>   it is compatible configuration, follows existing implementation,
>>   provides single pool and no description for segment sizes
>>   and offsets.
>> - mp is NULL, rx_conf.rx_seg is not NULL, rx_conf.rx_nseg is not
>>   zero, it provides the extended configuration, individually for
>>   each segment.
>>
>> f the Rx queue is configured with new settings the packets being
>> received will be split into multiple segments pushed to the mbufs
>> with specified attributes. The PMD will split the received packets
>> into multiple segments according to the specification in the
>> description array.
>>
>> For example, let's suppose we configured the Rx queue with the
>> following segments:
>>     seg0 - pool0, len0=14B, off0=2
>>     seg1 - pool1, len1=20B, off1=128B
>>     seg2 - pool2, len2=20B, off2=0B
>>     seg3 - pool3, len3=512B, off3=0B
>>
>> The packet 46 bytes long will look like the following:
>>     seg0 - 14B long @ RTE_PKTMBUF_HEADROOM + 2 in mbuf from pool0
>>     seg1 - 20B long @ 128 in mbuf from pool1
>>     seg2 - 12B long @ 0 in mbuf from pool2
>>
>> The packet 1500 bytes long will look like the following:
>>     seg0 - 14B @ RTE_PKTMBUF_HEADROOM + 2 in mbuf from pool0
>>     seg1 - 20B @ 128 in mbuf from pool1
>>     seg2 - 20B @ 0 in mbuf from pool2
>>     seg3 - 512B @ 0 in mbuf from pool3
>>     seg4 - 512B @ 0 in mbuf from pool3
>>     seg5 - 422B @ 0 in mbuf from pool3
>>
>> The offload RTE_ETH_RX_OFFLOAD_SCATTER must be present and
>> configured to support new buffer split feature (if rx_nseg
>> is greater than one).
>>
>> The split limitations imposed by underlying PMD is reported
>> in the new introduced rte_eth_dev_info->rx_seg_capa field.
>>
>> The new approach would allow splitting the ingress packets into
>> multiple parts pushed to the memory with different attributes.
>> For example, the packet headers can be pushed to the embedded
>> data buffers within mbufs and the application data into
>> the external buffers attached to mbufs allocated from the
>> different memory pools. The memory attributes for the split
>> parts may differ either - for example the application data
>> may be pushed into the external memory located on the dedicated
>> physical device, say GPU or NVMe. This would improve the DPDK
>> receiving datapath flexibility with preserving compatibility
>> with existing API.
>>
>> Signed-off-by: Viacheslav Ovsiienko <viacheslavo@nvidia.com>
>> Acked-by: Ajit Khaparde <ajit.khaparde@broadcom.com>
>> Acked-by: Jerin Jacob <jerinj@marvell.com>

With below review notes processed:
Reviewed-by: Andrew Rybchenko <andrew.rybchenko@oktetlabs.ru>

>> ---
>>  doc/guides/nics/features.rst           |  15 ++++
>>  doc/guides/rel_notes/deprecation.rst   |   5 --
>>  doc/guides/rel_notes/release_20_11.rst |   9 ++
>>  lib/librte_ethdev/rte_ethdev.c         | 152 +++++++++++++++++++++++++++------
>>  lib/librte_ethdev/rte_ethdev.h         |  88 ++++++++++++++++++-
>>  5 files changed, 238 insertions(+), 31 deletions(-)
>>
>> diff --git a/doc/guides/nics/features.rst b/doc/guides/nics/features.rst
>> index dd8c955..832ea3b 100644
>> --- a/doc/guides/nics/features.rst
>> +++ b/doc/guides/nics/features.rst
>> @@ -185,6 +185,21 @@ Supports receiving segmented mbufs.
>>  * **[related]    eth_dev_ops**: ``rx_pkt_burst``.
>>  
>>  
>> +.. _nic_features_buffer_split:
>> +
>> +Buffer Split on Rx
>> +------------------
>> +
>> +Scatters the packets being received on specified boundaries to segmented mbufs.
>> +
>> +* **[uses]       rte_eth_rxconf,rte_eth_rxmode**: ``offloads:RTE_ETH_RX_OFFLOAD_BUFFER_SPLIT``.
>> +* **[uses]       rte_eth_rxconf**: ``rx_conf.rx_seg, rx_conf.rx_nseg``.
>> +* **[implements] datapath**: ``Buffer Split functionality``.
>> +* **[provides]   rte_eth_dev_info**: ``rx_offload_capa:RTE_ETH_RX_OFFLOAD_BUFFER_SPLIT``.
>> +* **[provides]   eth_dev_ops**: ``rxq_info_get:buffer_split``.
>> +* **[related] API**: ``rte_eth_rx_queue_setup()``.
>> +
>> +
>>  .. _nic_features_lro:
>>  
>>  LRO
>> diff --git a/doc/guides/rel_notes/deprecation.rst b/doc/guides/rel_notes/deprecation.rst
>> index 584e720..232cd54 100644
>> --- a/doc/guides/rel_notes/deprecation.rst
>> +++ b/doc/guides/rel_notes/deprecation.rst
>> @@ -138,11 +138,6 @@ Deprecation Notices
>>    In 19.11 PMDs will still update the field even when the offload is not
>>    enabled.
>>  
>> -* ethdev: Add new fields to ``rte_eth_rxconf`` to configure the receiving
>> -  queues to split ingress packets into multiple segments according to the
>> -  specified lengths into the buffers allocated from the specified
>> -  memory pools. The backward compatibility to existing API is preserved.
>> -
>>  * ethdev: ``rx_descriptor_done`` dev_ops and ``rte_eth_rx_descriptor_done``
>>    will be removed in 21.11.
>>    Existing ``rte_eth_rx_descriptor_status`` and ``rte_eth_tx_descriptor_status``
>> diff --git a/doc/guides/rel_notes/release_20_11.rst b/doc/guides/rel_notes/release_20_11.rst
>> index bcc0fc2..bcc2479 100644
>> --- a/doc/guides/rel_notes/release_20_11.rst
>> +++ b/doc/guides/rel_notes/release_20_11.rst
>> @@ -60,6 +60,12 @@ New Features
>>    Added the FEC API which provides functions for query FEC capabilities and
>>    current FEC mode from device. Also, API for configuring FEC mode is also provided.
>>  
>> +* **Introduced extended buffer description for receiving.**
>> +
>> +  Added the extended Rx buffer description for Rx queue setup routine
>> +  providing the individual settings for each Rx segment with maximal size,
>> +  buffer offset and memory pool to allocate data buffers from.
>> +
>>  * **Updated Broadcom bnxt driver.**
>>  
>>    Updated the Broadcom bnxt driver with new features and improvements, including:
>> @@ -253,6 +259,9 @@ API Changes
>>    As the data of ``uint8_t`` will be truncated when queue number under
>>    a TC is greater than 256.
>>  
>> +* ethdev: Added fields rx_seg and rx_nseg to rte_eth_rxconf structure
>> +  to provide extended description of the receiving buffer.
>> +
>>  * vhost: Moved vDPA APIs from experimental to stable.
>>  
>>  * rawdev: Added a structure size parameter to the functions
>> diff --git a/lib/librte_ethdev/rte_ethdev.c b/lib/librte_ethdev/rte_ethdev.c
>> index 892c246..0eda3f4 100644
>> --- a/lib/librte_ethdev/rte_ethdev.c
>> +++ b/lib/librte_ethdev/rte_ethdev.c
>> @@ -105,6 +105,9 @@ struct rte_eth_xstats_name_off {
>>  #define RTE_RX_OFFLOAD_BIT2STR(_name)	\
>>  	{ DEV_RX_OFFLOAD_##_name, #_name }
>>  
>> +#define RTE_ETH_RX_OFFLOAD_BIT2STR(_name)	\
>> +	{ RTE_ETH_RX_OFFLOAD_##_name, #_name }
>> +
>>  static const struct {
>>  	uint64_t offload;
>>  	const char *name;
>> @@ -128,9 +131,11 @@ struct rte_eth_xstats_name_off {
>>  	RTE_RX_OFFLOAD_BIT2STR(SCTP_CKSUM),
>>  	RTE_RX_OFFLOAD_BIT2STR(OUTER_UDP_CKSUM),
>>  	RTE_RX_OFFLOAD_BIT2STR(RSS_HASH),
>> +	RTE_ETH_RX_OFFLOAD_BIT2STR(BUFFER_SPLIT),
>>  };
>>  
>>  #undef RTE_RX_OFFLOAD_BIT2STR
>> +#undef RTE_ETH_RX_OFFLOAD_BIT2STR
>>  
>>  #define RTE_TX_OFFLOAD_BIT2STR(_name)	\
>>  	{ DEV_TX_OFFLOAD_##_name, #_name }
>> @@ -1763,6 +1768,77 @@ struct rte_eth_dev *
>>  	return ret;
>>  }
>>  
>> +static int
>> +rte_eth_rx_queue_check_split(const struct rte_eth_rxseg *rx_seg,
>> +			     uint16_t n_seg, uint32_t *mbp_buf_size,
>> +			     const struct rte_eth_dev_info *dev_info)
>> +{
>> +	const struct rte_eth_rxseg_capa *seg_capa = &dev_info->rx_seg_capa;
>> +	struct rte_mempool *mp_first;
>> +	uint32_t offset_mask;
>> +	uint16_t seg_idx;
>> +
>> +	if (n_seg > seg_capa->max_seg) {
>> +		RTE_ETHDEV_LOG(ERR,
>> +			       "Requested Rx segments %u exceed supported %u\n",
>> +			       n_seg, seg_capa->max_seg);
>> +		return -EINVAL;
>> +	}
>> +	/*
>> +	 * Check the sizes and offsets against buffer sizes
>> +	 * for each segment specified in extended configuration.
>> +	 */
>> +	mp_first = rx_seg[0].conf.split.mp;
>> +	offset_mask = (1u << seg_capa->offset_align_log2) - 1;
>> +	for (seg_idx = 0; seg_idx < n_seg; seg_idx++) {
>> +		struct rte_mempool *mpl = rx_seg[seg_idx].conf.split.mp;
>> +		uint32_t length = rx_seg[seg_idx].conf.split.length;
>> +		uint32_t offset = rx_seg[seg_idx].conf.split.offset;
>> +
>> +		if (mpl == NULL) {
>> +			RTE_ETHDEV_LOG(ERR, "null mempool pointer\n");
>> +			return -EINVAL;
>> +		}
>> +		if (seg_idx != 0 && mp_first != mpl &&
>> +		    seg_capa->multi_pools == 0) {
>> +			RTE_ETHDEV_LOG(ERR, "Receiving to multiple pools is not supported\n");
>> +			return -ENOTSUP;
>> +		}
>> +		if (offset != 0) {
>> +			if (seg_capa->offset_allowed == 0) {
>> +				RTE_ETHDEV_LOG(ERR, "Rx segmentation with offset is not supported\n");
>> +				return -ENOTSUP;
>> +			}
>> +			if (offset & offset_mask) {
>> +				RTE_ETHDEV_LOG(ERR, "Rx segmentat invalid offset alignment %u, %u\n",
>> +					       offset,
>> +					       seg_capa->offset_align_log2);
>> +				return -EINVAL;
>> +			}
>> +		}
>> +		if (mpl->private_data_size <
>> +			sizeof(struct rte_pktmbuf_pool_private)) {
>> +			RTE_ETHDEV_LOG(ERR,
>> +				       "%s private_data_size %u < %u\n",
>> +				       mpl->name, mpl->private_data_size,
>> +				       (unsigned int)sizeof
>> +					(struct rte_pktmbuf_pool_private));
>> +			return -ENOSPC;
>> +		}
>> +		offset += seg_idx != 0 ? 0 : RTE_PKTMBUF_HEADROOM;
>> +		*mbp_buf_size = rte_pktmbuf_data_room_size(mpl);
>> +		length = length != 0 ? length : *mbp_buf_size;
>> +		if (*mbp_buf_size < length + offset) {
>> +			RTE_ETHDEV_LOG(ERR,
>> +				       "%s mbuf_data_room_size %u < %u (segment length=%u + segment offset=%u)\n",
>> +				       mpl->name, *mbp_buf_size,
>> +				       length + offset, length, offset);
>> +			return -EINVAL;
>> +		}
>> +	}
>> +	return 0;
>> +}
>> +
>>  int
>>  rte_eth_rx_queue_setup(uint16_t port_id, uint16_t rx_queue_id,
>>  		       uint16_t nb_rx_desc, unsigned int socket_id,
>> @@ -1784,38 +1860,64 @@ struct rte_eth_dev *
>>  		return -EINVAL;
>>  	}
>>  
>> -	if (mp == NULL) {
>> -		RTE_ETHDEV_LOG(ERR, "Invalid null mempool pointer\n");
>> -		return -EINVAL;
>> -	}
>> -
>>  	RTE_FUNC_PTR_OR_ERR_RET(*dev->dev_ops->rx_queue_setup, -ENOTSUP);
>>  
>> -	/*
>> -	 * Check the size of the mbuf data buffer.
>> -	 * This value must be provided in the private data of the memory pool.
>> -	 * First check that the memory pool has a valid private data.
>> -	 */
>>  	ret = rte_eth_dev_info_get(port_id, &dev_info);
>>  	if (ret != 0)
>>  		return ret;
>>  
>> -	if (mp->private_data_size < sizeof(struct rte_pktmbuf_pool_private)) {
>> -		RTE_ETHDEV_LOG(ERR, "%s private_data_size %d < %d\n",
>> -			mp->name, (int)mp->private_data_size,
>> -			(int)sizeof(struct rte_pktmbuf_pool_private));
>> -		return -ENOSPC;
>> -	}
>> -	mbp_buf_size = rte_pktmbuf_data_room_size(mp);
>> +	if (mp != NULL) {
>> +		/* Single pool configuration check. */
>> +		if (rx_conf->rx_nseg != 0) {
>> +			RTE_ETHDEV_LOG(ERR,
>> +				       "Ambiguous segment configuration\n");
>> +			return -EINVAL;
>> +		}
>> +		/*
>> +		 * Check the size of the mbuf data buffer, this value
>> +		 * must be provided in the private data of the memory pool.
>> +		 * First check that the memory pool(s) has a valid private data.
>> +		 */
>> +		if (mp->private_data_size <
>> +				sizeof(struct rte_pktmbuf_pool_private)) {
>> +			RTE_ETHDEV_LOG(ERR, "%s private_data_size %u < %u\n",
>> +				mp->name, mp->private_data_size,
>> +				(unsigned int)
>> +				sizeof(struct rte_pktmbuf_pool_private));
>> +			return -ENOSPC;
>> +		}
>> +		mbp_buf_size = rte_pktmbuf_data_room_size(mp);
>> +		if (mbp_buf_size < dev_info.min_rx_bufsize +
>> +				   RTE_PKTMBUF_HEADROOM) {
>> +			RTE_ETHDEV_LOG(ERR,
>> +				       "%s mbuf_data_room_size %u < %u (RTE_PKTMBUF_HEADROOM=%u + min_rx_bufsize(dev)=%u)\n",
>> +				       mp->name, mbp_buf_size,
>> +				       RTE_PKTMBUF_HEADROOM +
>> +				       dev_info.min_rx_bufsize,
>> +				       RTE_PKTMBUF_HEADROOM,
>> +				       dev_info.min_rx_bufsize);
>> +			return -EINVAL;
>> +		}
>> +	} else {
>> +		const struct rte_eth_rxseg *rx_seg = rx_conf->rx_seg;
>> +		uint16_t n_seg = rx_conf->rx_nseg;
>>  
>> -	if (mbp_buf_size < dev_info.min_rx_bufsize + RTE_PKTMBUF_HEADROOM) {
>> -		RTE_ETHDEV_LOG(ERR,
>> -			"%s mbuf_data_room_size %d < %d (RTE_PKTMBUF_HEADROOM=%d + min_rx_bufsize(dev)=%d)\n",
>> -			mp->name, (int)mbp_buf_size,
>> -			(int)(RTE_PKTMBUF_HEADROOM + dev_info.min_rx_bufsize),
>> -			(int)RTE_PKTMBUF_HEADROOM,
>> -			(int)dev_info.min_rx_bufsize);
>> -		return -EINVAL;
>> +		/* Extended multi-segment configuration check. */
>> +		if (rx_conf->rx_seg == NULL || rx_conf->rx_nseg == 0) {
>> +			RTE_ETHDEV_LOG(ERR,
>> +				       "Memory pool is null and no extended configuration provided\n");
>> +			return -EINVAL;
>> +		}
>> +		if (rx_conf->offloads & RTE_ETH_RX_OFFLOAD_BUFFER_SPLIT) {
>> +			ret = rte_eth_rx_queue_check_split(rx_seg, n_seg,
>> +							   &mbp_buf_size,
>> +							   &dev_info);
>> +			if (ret != 0)
>> +				return ret;
>> +		} else {
>> +			RTE_ETHDEV_LOG(ERR, "No Rx segmentation offload configured\n");
>> +			return -EINVAL;
>> +		}
>>  	}
>>  
>>  	/* Use default specified by driver, if nb_rx_desc is zero */
>> diff --git a/lib/librte_ethdev/rte_ethdev.h b/lib/librte_ethdev/rte_ethdev.h
>> index 5bcfbb8..6f18bec 100644
>> --- a/lib/librte_ethdev/rte_ethdev.h
>> +++ b/lib/librte_ethdev/rte_ethdev.h
>> @@ -970,6 +970,27 @@ struct rte_eth_txmode {
>>  };
>>  
>>  /**
>> + * A structure used to configure an Rx packet segment to split.
>> + */
>> +struct rte_eth_rxseg_split {
>> +	struct rte_mempool *mp; /**< Memory pool to allocate segment from. */
>> +	uint16_t length; /**< Segment data length, configures split point. */
>> +	uint16_t offset; /**< Data offset from beginning of mbuf data buffer. */
>> +	uint32_t reserved; /**< Reserved field. */
>> +};
>> +
>> +/**
>> + * A common structure used to describe Rx packet segment properties.
>> + */
>> +struct rte_eth_rxseg {
>> +	union {
> 
> Why not just 'union rte_eth_rxseg' ?
> 
>> +		/* The settings for buffer split offload. */
>> +		struct rte_eth_rxseg_split split;
> 
> Pointer to a split table must be here. I.e.
> struct rte_eth_rxseg_split *split;
> Also it must be specified how the array is terminated.
> We need either a number of define last item condition
> (mp == NULL ?)
> 
>> +		/* The other features settings should be added here. */
>> +	} conf;
>> +};
> 
> 
> 
>> +
>> +/**
>>   * A structure used to configure an RX ring of an Ethernet port.
>>   */
>>  struct rte_eth_rxconf {
>> @@ -977,6 +998,46 @@ struct rte_eth_rxconf {
>>  	uint16_t rx_free_thresh; /**< Drives the freeing of RX descriptors. */
>>  	uint8_t rx_drop_en; /**< Drop packets if no descriptors are available. */
>>  	uint8_t rx_deferred_start; /**< Do not start queue with rte_eth_dev_start(). */
>> +	uint16_t rx_nseg; /**< Number of descriptions in rx_seg array. */
>> +	/**
>> +	 * Points to the array of segment descriptions. Each array element
>> +	 * describes the properties for each segment in the receiving
>> +	 * buffer according to feature descripting structure.
>> +	 *
>> +	 * The supported capabilities of receiving segmentation is reported
>> +	 * in rte_eth_dev_info ->rx_seg_capa field.
>> +	 *
>> +	 * If RTE_ETH_RX_OFFLOAD_BUFFER_SPLIT flag is set in offloads field,
>> +	 * the PMD will split the received packets into multiple segments
>> +	 * according to the specification in the description array:
>> +	 *
>> +	 * - the first network buffer will be allocated from the memory pool,
>> +	 *   specified in the first array element, the second buffer, from the
>> +	 *   pool in the second element, and so on.
>> +	 *
>> +	 * - the offsets from the segment description elements specify
>> +	 *   the data offset from the buffer beginning except the first mbuf.
>> +	 *   For this one the offset is added with RTE_PKTMBUF_HEADROOM.
>> +	 *
>> +	 * - the lengths in the elements define the maximal data amount
>> +	 *   being received to each segment. The receiving starts with filling
>> +	 *   up the first mbuf data buffer up to specified length. If the
>> +	 *   there are data remaining (packet is longer than buffer in the first
>> +	 *   mbuf) the following data will be pushed to the next segment
>> +	 *   up to its own length, and so on.
>> +	 *
>> +	 * - If the length in the segment description element is zero
>> +	 *   the actual buffer size will be deduced from the appropriate
>> +	 *   memory pool properties.
>> +	 *
>> +	 * - if there is not enough elements to describe the buffer for entire
>> +	 *   packet of maximal length the following parameters will be used
>> +	 *   for the all remaining segments:
>> +	 *     - pool from the last valid element
>> +	 *     - the buffer size from this pool
>> +	 *     - zero offset
>> +	 */
>> +	struct rte_eth_rxseg *rx_seg;
> 
> It must not be a pointer. It looks really strange this way
> taking into account that it is a union in fact.
> Also, why is it put here in the middle of exsiting structure?
> IMHO it should be added after offlaods.
> 
>>  	/**
>>  	 * Per-queue Rx offloads to be set using DEV_RX_OFFLOAD_* flags.
>>  	 * Only offloads set on rx_queue_offload_capa or rx_offload_capa
>> @@ -1260,6 +1321,7 @@ struct rte_eth_conf {
>>  #define DEV_RX_OFFLOAD_SCTP_CKSUM	0x00020000
>>  #define DEV_RX_OFFLOAD_OUTER_UDP_CKSUM  0x00040000
>>  #define DEV_RX_OFFLOAD_RSS_HASH		0x00080000
>> +#define RTE_ETH_RX_OFFLOAD_BUFFER_SPLIT 0x00100000
>>  
>>  #define DEV_RX_OFFLOAD_CHECKSUM (DEV_RX_OFFLOAD_IPV4_CKSUM | \
>>  				 DEV_RX_OFFLOAD_UDP_CKSUM | \
>> @@ -1376,6 +1438,17 @@ struct rte_eth_switch_info {
>>  };
>>  
>>  /**
>> + * Ethernet device Rx buffer segmentation capabilities.
>> + */
>> +__extension__
>> +struct rte_eth_rxseg_capa {
>> +	uint16_t max_seg; /**< Maximum amount of segments to split. */
> 
> May be 'max_segs' to avoid confusing vs maximum segment length.
> 
>> +	uint16_t multi_pools:1; /**< Supports receiving to multiple pools.*/
>> +	uint16_t offset_allowed:1; /**< Supports buffer offsets. */
>> +	uint16_t offset_align_log2:4; /**< Required offset alignment. */
> 
> 4 bits are even insufficient to specify cache-line alignment.
> IMHO at least 8 bits are required.
> 
> Consider to put 32 width bit-fields at start of the structure.
> Than, max_segs (16), offset_align_log2 (8), plus reserved (8).
> 
>> +};
>> +
>> +/**
>>   * Ethernet device information
>>   */
>>  
>> @@ -1403,6 +1476,7 @@ struct rte_eth_dev_info {
>>  	/** Maximum number of hash MAC addresses for MTA and UTA. */
>>  	uint16_t max_vfs; /**< Maximum number of VFs. */
>>  	uint16_t max_vmdq_pools; /**< Maximum number of VMDq pools. */
>> +	struct rte_eth_rxseg_capa rx_seg_capa; /**< Segmentation capability.*/
> 
> Why is it put in the middle of existing structure?
> 
>>  	uint64_t rx_offload_capa;
>>  	/**< All RX offload capabilities including all per-queue ones */
>>  	uint64_t tx_offload_capa;
>> @@ -2027,9 +2101,21 @@ int rte_eth_dev_configure(uint16_t port_id, uint16_t nb_rx_queue,
>>   *   No need to repeat any bit in rx_conf->offloads which has already been
>>   *   enabled in rte_eth_dev_configure() at port level. An offloading enabled
>>   *   at port level can't be disabled at queue level.
>> + *   The configuration structure also contains the pointer to the array
>> + *   of the receiving buffer segment descriptions, see rx_seg and rx_nseg
>> + *   fields, this extended configuration might be used by split offloads like
>> + *   RTE_ETH_RX_OFFLOAD_BUFFER_SPLIT. If mp_pool is not NULL,
>> + *   the extended configuration fields must be set to NULL and zero.
>>   * @param mb_pool
>>   *   The pointer to the memory pool from which to allocate *rte_mbuf* network
>> - *   memory buffers to populate each descriptor of the receive ring.
>> + *   memory buffers to populate each descriptor of the receive ring. There are
>> + *   two options to provide Rx buffer configuration:
>> + *   - single pool:
>> + *     mb_pool is not NULL, rx_conf.rx_seg is NULL, rx_conf.rx_nseg is 0.
>> + *   - multiple segments description:
>> + *     mb_pool is NULL, rx_conf.rx_seg is not NULL, rx_conf.rx_nseg is not 0.
>> + *     Taken only if flag RTE_ETH_RX_OFFLOAD_BUFFER_SPLIT is set in offloads.
>> + *
>>   * @return
>>   *   - 0: Success, receive queue correctly set up.
>>   *   - -EIO: if device is removed.
>>
>