RE: [PATCH v8 1/3] ethdev: introduce protocol hdr based buffer split

["Ding, Xuan" <xuan.ding@intel.com>]

Hi Andrew,

> -----Original Message-----
> From: Andrew Rybchenko <andrew.rybchenko@oktetlabs.ru>
> Sent: Thursday, June 2, 2022 9:21 PM
> To: Wu, WenxuanX <wenxuanx.wu@intel.com>; thomas@monjalon.net; Li,
> Xiaoyun <xiaoyun.li@intel.com>; ferruh.yigit@xilinx.com; Singh, Aman Deep
> <aman.deep.singh@intel.com>; dev@dpdk.org; Zhang, Yuying
> <yuying.zhang@intel.com>; Zhang, Qi Z <qi.z.zhang@intel.com>;
> jerinjacobk@gmail.com
> Cc: stephen@networkplumber.org; Ding, Xuan <xuan.ding@intel.com>;
> Wang, YuanX <yuanx.wang@intel.com>; Ray Kinsella <mdr@ashroe.eu>
> Subject: Re: [PATCH v8 1/3] ethdev: introduce protocol hdr based buffer split
> 
> Is it the right one since it is listed in patchwork?

Yes, it is.

> 
> On 6/1/22 16:50, wenxuanx.wu@intel.com wrote:
> > From: Wenxuan Wu <wenxuanx.wu@intel.com>
> >
> > Currently, Rx buffer split supports length based split. With Rx queue
> > offload RTE_ETH_RX_OFFLOAD_BUFFER_SPLIT enabled and Rx packet
> segment
> > configured, PMD will be able to split the received packets into
> > multiple segments.
> >
> > However, length based buffer split is not suitable for NICs that do
> > split based on protocol headers. Given a arbitrarily variable length
> > in Rx packet
> 
> a -> an

Thanks for your catch, will fix it in next version.

> 
> > segment, it is almost impossible to pass a fixed protocol header to PMD.
> > Besides, the existence of tunneling results in the composition of a
> > packet is various, which makes the situation even worse.
> >
> > This patch extends current buffer split to support protocol header
> > based buffer split. A new proto_hdr field is introduced in the
> > reserved field of rte_eth_rxseg_split structure to specify protocol
> > header. The proto_hdr field defines the split position of packet,
> > splitting will always happens after the protocol header defined in the
> > Rx packet segment. When Rx queue offload
> > RTE_ETH_RX_OFFLOAD_BUFFER_SPLIT is enabled and corresponding
> protocol
> > header is configured, PMD will split the ingress packets into multiple
> segments.
> >
> > 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 proto_hdr; /* inner/outer L2/L3/L4 protocol header,
> > 			       configures "split point" */
> >      };
> >
> > Both inner and outer L2/L3/L4 level protocol header split can be supported.
> > Corresponding protocol header capability is RTE_PTYPE_L2_ETHER,
> > RTE_PTYPE_L3_IPV4, RTE_PTYPE_L3_IPV6, RTE_PTYPE_L4_TCP,
> > RTE_PTYPE_L4_UDP, RTE_PTYPE_L4_SCTP, RTE_PTYPE_INNER_L2_ETHER,
> > RTE_PTYPE_INNER_L3_IPV4, RTE_PTYPE_INNER_L3_IPV6,
> > RTE_PTYPE_INNER_L4_TCP, RTE_PTYPE_INNER_L4_UDP,
> RTE_PTYPE_INNER_L4_SCTP.
> >
> > For example, let's suppose we configured the Rx queue with the
> > following segments:
> >      seg0 - pool0, proto_hdr0=RTE_PTYPE_L3_IPV4, off0=2B
> >      seg1 - pool1, proto_hdr1=RTE_PTYPE_L4_UDP, off1=128B
> >      seg2 - pool2, off1=0B
> >
> > The packet consists of MAC_IPV4_UDP_PAYLOAD will be split like
> > following:
> >      seg0 - ipv4 header @ RTE_PKTMBUF_HEADROOM + 2 in mbuf from
> pool0
> >      seg1 - udp header @ 128 in mbuf from pool1
> >      seg2 - payload @ 0 in mbuf from pool2
> 
> It must be defined how ICMPv4 packets will be split in such case.
> And how UDP over IPv6 will be split.

The ICMP header type is missed, I will define the expected split behavior and
add it in next version, thanks for your catch.

In fact, the buffer split based on protocol header depends on the driver parsing result.
As long as driver can recognize this packet type, I think there is no difference between
UDP over IPV4 and UDP over IPV6?

> >
> > Now buffet split can be configured in two modes. For length based
> > buffer split, the mp, length, offset field in Rx packet segment should
> > be configured, while the proto_hdr field should not be configured.
> > For protocol header based buffer split, the mp, offset, proto_hdr
> > field in Rx packet segment should be configured, while the length
> > field should not be configured.
> >
> > The split limitations imposed by underlying PMD is reported in the
> > rte_eth_dev_info->rx_seg_capa field. The memory attributes for the
> > split parts may differ either, 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>
> > Acked-by: Ray Kinsella <mdr@ashroe.eu>
> > ---
> >   lib/ethdev/rte_ethdev.c | 40 +++++++++++++++++++++++++++++++++-------
> >   lib/ethdev/rte_ethdev.h | 28 +++++++++++++++++++++++++++-
> >   2 files changed, 60 insertions(+), 8 deletions(-)
> >
> > diff --git a/lib/ethdev/rte_ethdev.c b/lib/ethdev/rte_ethdev.c index
> > 29a3d80466..fbd55cdd9d 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;
> > +		uint32_t proto_hdr = rx_seg[seg_idx].proto_hdr;
> >
> >   		if (mpl == NULL) {
> >   			RTE_ETHDEV_LOG(ERR, "null mempool pointer\n");
> @@ -1694,13
> > +1695,38 @@ 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_hdr == RTE_PTYPE_UNKNOWN) {
> > +			/* Split at fixed length. */
> > +			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 {
> > +			/* Split after specified protocol header. */
> > +			if (!(proto_hdr &
> RTE_BUFFER_SPLIT_PROTO_HDR_MASK)) {
> 
> The condition looks suspicious. It will be true if proto_hdr has no single bit
> from the mask. I guess it is not the intent.

Actually it is the intent... Here the mask is used to check if proto_hdr
belongs to the inner/outer L2/L3/L4 capability we defined. And which
proto_hdr is supported by the NIC will be checked in the PMD later.

> I guess the condition should be
>    proto_hdr & ~RTE_BUFFER_SPLIT_PROTO_HDR_MASK i.e. there is
> unsupported bits in proto_hdr
> 
> IMHO we need extra field in dev_info to report supported protocols to split
> on. Or a new API to get an array similar to ptype get.
> May be a new API is a better choice to not overload dev_info and to be more
> flexible in reporting.

Thanks for your suggestion.
Here I hope to confirm the intent of dev_info or API to expose the supported proto_hdr of driver.
Is it for the pro_hdr check in the rte_eth_rx_queue_check_split()?
If so, could we just check whether pro_hdrs configured belongs to L2/L3/L4 in lib, and check the
capability in PMD? This is what the current design does.

Actually I have another question, do we need a API or dev_info to expose which buffer split the driver supports.
i.e. length based or proto_hdr based. Because it requires different fields to be configured
in RX packet segment.

Hope to get your insights. :)

> 
> > +				RTE_ETHDEV_LOG(ERR,
> > +					"Protocol header %u not
> supported)\n",
> > +					proto_hdr);
> 
> I think it would be useful to log unsupported bits only, if we say so.

The same as above.
Thanks again for your time.

Regards,
Xuan

> 
> > +				return -EINVAL;
> > +			}
> > +
> > +			if (length != 0) {
> > +				RTE_ETHDEV_LOG(ERR, "segment length
> should be set to zero in protocol header "
> > +					       "based buffer 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;
> > diff --git a/lib/ethdev/rte_ethdev.h b/lib/ethdev/rte_ethdev.h index
> > 04cff8ee10..0cd9dd6cc0 100644
> > --- a/lib/ethdev/rte_ethdev.h
> > +++ b/lib/ethdev/rte_ethdev.h
> > @@ -1187,6 +1187,9 @@ struct rte_eth_txmode {
> >    *   mbuf) the following data will be pushed to the next segment
> >    *   up to its own length, and so on.
> >    *
> > + * - The proto_hdrs in the elements define the split position of
> > + *   received packets.
> > + *
> >    * - If the length in the segment description element is zero
> >    *   the actual buffer size will be deduced from the appropriate
> >    *   memory pool properties.
> > @@ -1197,14 +1200,37 @@ struct rte_eth_txmode {
> >    *     - pool from the last valid element
> >    *     - the buffer size from this pool
> >    *     - zero offset
> > + *
> > + * - Length based buffer split:
> > + *     - mp, length, offset should be configured.
> > + *     - The proto_hdr field should not be configured.
> > + *
> > + * - Protocol header based buffer split:
> > + *     - mp, offset, proto_hdr should be configured.
> > + *     - The length field should not be configured.
> >    */
> >   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. */
> > +	uint32_t proto_hdr; /**< Inner/outer L2/L3/L4 protocol header,
> > +configures split point. */
> >   };
> >
> > +/* Buffer split protocol header capability. */ #define
> > +RTE_BUFFER_SPLIT_PROTO_HDR_MASK ( \
> > +	RTE_PTYPE_L2_ETHER | \
> > +	RTE_PTYPE_L3_IPV4 | \
> > +	RTE_PTYPE_L3_IPV6 | \
> > +	RTE_PTYPE_L4_TCP | \
> > +	RTE_PTYPE_L4_UDP | \
> > +	RTE_PTYPE_L4_SCTP | \
> > +	RTE_PTYPE_INNER_L2_ETHER | \
> > +	RTE_PTYPE_INNER_L3_IPV4 | \
> > +	RTE_PTYPE_INNER_L3_IPV6 | \
> > +	RTE_PTYPE_INNER_L4_TCP | \
> > +	RTE_PTYPE_INNER_L4_UDP | \
> > +	RTE_PTYPE_INNER_L4_SCTP)
> > +
> >   /**
> >    * @warning
> >    * @b EXPERIMENTAL: this structure may change without prior notice.