Re: [v4 1/3] ethdev: introduce protocol type based header split

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

On 4/2/22 13:41, wenxuanx.wu@intel.com wrote:
> From: Xuan Ding <xuan.ding@intel.com>
> 
> Header split consists of splitting a received packet into two separate
> regions based on the packet content. The split happens after the
> packet header and before the packet payload. Splitting is usually between
> the packet header that can be posted to a dedicated buffer and the packet
> payload that can be posted to a different buffer.
> 
> Currently, Rx buffer split supports length and offset based packet split.
> Although header split is a subset of buffer split, configuring buffer
> split based on length is not suitable for NICs that do split based on
> header protocol types. Because tunneling makes the conversion from length
> to protocol type impossible.
> 
> This patch extends the current buffer split to support protocol type and
> offset based header split. A new proto field is introduced in the
> rte_eth_rxseg_split structure reserved field to specify header protocol
> type. With Rx offload flag RTE_ETH_RX_OFFLOAD_HEADER_SPLIT enabled and
> protocol type configured, PMD will split the ingress packets into two
> separate regions. Currently, both inner and outer L2/L3/L4 level header
> split can be supported.

RTE_ETH_RX_OFFLOAD_HEADER_SPLIT offload was introduced some
time ago to substitute bit-field header_split in struct
rte_eth_rxmode. It allows to enable header split offload with
the header size controlled using split_hdr_size in the same
structure.

Right now I see no single PMD which actually supports
RTE_ETH_RX_OFFLOAD_HEADER_SPLIT with above definition.
Many examples and test apps initialize the field to 0
explicitly. The most of drivers simply ignore split_hdr_size
since the offload is not advertised, but some double-check
that its value is 0.

I think that it means that the field should be removed on
the next LTS, and I'd say, together with the
RTE_ETH_RX_OFFLOAD_HEADER_SPLIT offload bit.

We should not redefine the offload meaning. 
 
 
 
 
 
 
 
 
 
 
 
 
 


> 
> For example, let's suppose we configured the Rx queue with the
> following segments:
>      seg0 - pool0, off0=2B
>      seg1 - pool1, off1=128B

Corresponding feature is named Rx buffer split.
Does it mean that protocol type based header split
requires Rx buffer split feature to be supported?

> 
> With header split type configured with RTE_ETH_RX_HEADER_SPLIT_UDP,
> the packet consists of MAC_IP_UDP_PAYLOAD will be split like following:
>      seg0 - udp header @ RTE_PKTMBUF_HEADROOM + 2 in mbuf from pool0
>      seg1 - payload @ 128 in mbuf from pool1

Is it always outermost UDP? Does it require both UDP over IPv4
and UDP over IPv6 to be supported? What will happen if only one
is supported? How application can find out which protocol stack
are supported?

> 
> The memory attributes for the split parts may differ either - for example
> the mempool0 and mempool1 belong to dpdk memory and external memory,
> respectively.
> 
> Signed-off-by: Xuan Ding <xuan.ding@intel.com>
> Signed-off-by: Yuan Wang <yuanx.wang@intel.com>
> Signed-off-by: Wenxuan Wu <wenxuanx.wu@intel.com>
> Reviewed-by: Qi Zhang <qi.z.zhang@intel.com>
> ---
>   lib/ethdev/rte_ethdev.c | 34 ++++++++++++++++++++++-------
>   lib/ethdev/rte_ethdev.h | 48 +++++++++++++++++++++++++++++++++++++++--
>   2 files changed, 72 insertions(+), 10 deletions(-)
> 
> diff --git a/lib/ethdev/rte_ethdev.c b/lib/ethdev/rte_ethdev.c
> index 29a3d80466..29adcdc2f0 100644
> --- a/lib/ethdev/rte_ethdev.c
> +++ b/lib/ethdev/rte_ethdev.c
> @@ -1661,6 +1661,7 @@ rte_eth_rx_queue_check_split(const struct rte_eth_rxseg_split *rx_seg,
>   		struct rte_mempool *mpl = rx_seg[seg_idx].mp;
>   		uint32_t length = rx_seg[seg_idx].length;
>   		uint32_t offset = rx_seg[seg_idx].offset;
> +		uint16_t proto = rx_seg[seg_idx].proto;
>   
>   		if (mpl == NULL) {
>   			RTE_ETHDEV_LOG(ERR, "null mempool pointer\n");
> @@ -1694,13 +1695,29 @@ rte_eth_rx_queue_check_split(const struct rte_eth_rxseg_split *rx_seg,
>   		}
>   		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;
> +		if (proto == RTE_ETH_RX_HEADER_SPLIT_NONE) {
> +			/* Check buffer split. */
> +			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;
> +			}
> +		} else {
> +			/* Check header split. */
> +			if (length != 0) {
> +				RTE_ETHDEV_LOG(ERR, "segment length should be set to zero in header split\n");
> +				return -EINVAL;
> +			}
> +			if (*mbp_buf_size < offset) {
> +				RTE_ETHDEV_LOG(ERR,
> +					"%s mbuf_data_room_size %u < %u segment offset)\n",
> +					mpl->name, *mbp_buf_size,
> +					offset);
> +				return -EINVAL;
> +			}
>   		}
>   	}
>   	return 0;
> @@ -1778,7 +1795,8 @@ rte_eth_rx_queue_setup(uint16_t port_id, uint16_t rx_queue_id,
>   		rx_seg = (const struct rte_eth_rxseg_split *)rx_conf->rx_seg;
>   		n_seg = rx_conf->rx_nseg;
>   
> -		if (rx_conf->offloads & RTE_ETH_RX_OFFLOAD_BUFFER_SPLIT) {
> +		if (rx_conf->offloads & RTE_ETH_RX_OFFLOAD_BUFFER_SPLIT ||
> +			rx_conf->offloads & RTE_ETH_RX_OFFLOAD_HEADER_SPLIT) {
>   			ret = rte_eth_rx_queue_check_split(rx_seg, n_seg,
>   							   &mbp_buf_size,
>   							   &dev_info);
> diff --git a/lib/ethdev/rte_ethdev.h b/lib/ethdev/rte_ethdev.h
> index 04cff8ee10..e8371b98ed 100644
> --- a/lib/ethdev/rte_ethdev.h
> +++ b/lib/ethdev/rte_ethdev.h
> @@ -1197,12 +1197,31 @@ struct rte_eth_txmode {
>    *     - pool from the last valid element
>    *     - the buffer size from this pool
>    *     - zero offset
> + *
> + * Header split is a subset of buffer split. The split happens after the
> + * packet header and before the packet payload. For PMDs that do not
> + * support header split configuration by length, the location of the split
> + * needs to be specified by the header protocol type. While for buffer split,
> + * this field should not be configured.
> + *
> + * If RTE_ETH_RX_OFFLOAD_HEADER_SPLIT flag is set in offloads field,
> + * the PMD will split the received packets into two separate regions:
> + * - The header buffer will be allocated from the memory pool,
> + *   specified in the first array element, the second buffer, from the
> + *   pool in the second element.
> + *
> + * - The lengths do not need to be configured in header split.
> + *
> + * - The offsets from the segment description elements specify
> + *   the data offset from the buffer beginning except the first mbuf.
> + *   The first segment offset is added with RTE_PKTMBUF_HEADROOM.
>    */
>   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. */
> +	uint16_t proto; /**< header protocol type, configures header split point. */

I realize that you don't want to use here enum defined above to
save some reserved space, but description must refer to the
enum rte_eth_rx_header_split_protocol_type.

> +	uint16_t reserved; /**< Reserved field. */

As far as I can see the structure is experimental. So, it
should not be the problem to extend it, but it is a really
good question raised by Stephen in RFC v1 discussion.
Shouldn't we require that all reserved fields are initialized
to zero and ignored on processing? Frankly speaking I always
thought so, but failed to find the place were it is documented.

@Thomas, @David, @Ferruh?

>   };
>   
>   /**
> @@ -1212,7 +1231,7 @@ struct rte_eth_rxseg_split {
>    * A common structure used to describe Rx packet segment properties.
>    */
>   union rte_eth_rxseg {
> -	/* The settings for buffer split offload. */
> +	/* The settings for buffer split and header split offload. */
>   	struct rte_eth_rxseg_split split;
>   	/* The other features settings should be added here. */
>   };
> @@ -1664,6 +1683,31 @@ struct rte_eth_conf {
>   			     RTE_ETH_RX_OFFLOAD_QINQ_STRIP)
>   #define DEV_RX_OFFLOAD_VLAN RTE_DEPRECATED(DEV_RX_OFFLOAD_VLAN) RTE_ETH_RX_OFFLOAD_VLAN
>   
> +/**
> + * @warning
> + * @b EXPERIMENTAL: this enum may change without prior notice.
> + * This enum indicates the header split protocol type
> + */
> +enum rte_eth_rx_header_split_protocol_type {
> +	RTE_ETH_RX_HEADER_SPLIT_NONE = 0,
> +	RTE_ETH_RX_HEADER_SPLIT_MAC,
> +	RTE_ETH_RX_HEADER_SPLIT_IPV4,
> +	RTE_ETH_RX_HEADER_SPLIT_IPV6,
> +	RTE_ETH_RX_HEADER_SPLIT_L3,
> +	RTE_ETH_RX_HEADER_SPLIT_TCP,
> +	RTE_ETH_RX_HEADER_SPLIT_UDP,
> +	RTE_ETH_RX_HEADER_SPLIT_SCTP,
> +	RTE_ETH_RX_HEADER_SPLIT_L4,
> +	RTE_ETH_RX_HEADER_SPLIT_INNER_MAC,
> +	RTE_ETH_RX_HEADER_SPLIT_INNER_IPV4,
> +	RTE_ETH_RX_HEADER_SPLIT_INNER_IPV6,
> +	RTE_ETH_RX_HEADER_SPLIT_INNER_L3,
> +	RTE_ETH_RX_HEADER_SPLIT_INNER_TCP,
> +	RTE_ETH_RX_HEADER_SPLIT_INNER_UDP,
> +	RTE_ETH_RX_HEADER_SPLIT_INNER_SCTP,
> +	RTE_ETH_RX_HEADER_SPLIT_INNER_L4,

Enumeration members should be documented. See my question
in the patch description.

> +};
> +
>   /*
>    * If new Rx offload capabilities are defined, they also must be
>    * mentioned in rte_rx_offload_names in rte_ethdev.c file.