Re: [dpdk-dev] [RFC 1/3] ethdev: extend flow metadata

["Wang, Haiyue" <haiyue.wang@intel.com>]

> -----Original Message-----
> From: dev [mailto:dev-bounces@dpdk.org] On Behalf Of Andrew Rybchenko
> Sent: Sunday, June 9, 2019 22:24
> To: Yongseok Koh <yskoh@mellanox.com>; shahafs@mellanox.com; thomas@monjalon.net; Yigit, Ferruh
> <ferruh.yigit@intel.com>; adrien.mazarguil@6wind.com; olivier.matz@6wind.com
> Cc: dev@dpdk.org
> Subject: Re: [dpdk-dev] [RFC 1/3] ethdev: extend flow metadata
> 
> On 6/4/19 12:32 AM, Yongseok Koh wrote:
> > Currently, metadata can be set on egress path via mbuf tx_meatadata field
> > with PKT_TX_METADATA flag and RTE_FLOW_ITEM_TYPE_RX_META matches metadata.
> >
> > This patch extends the usability.
> >
> > 1) RTE_FLOW_ACTION_TYPE_SET_META
> >
> > When supporting multiple tables, Tx metadata can also be set by a rule and
> > matched by another rule. This new action allows metadata to be set as a
> > result of flow match.
> >
> > 2) Metadata on ingress
> >
> > There's also need to support metadata on packet Rx. Metadata can be set by
> > SET_META action and matched by META item like Tx. The final value set by
> > the action will be delivered to application via mbuf metadata field with
> > PKT_RX_METADATA ol_flag.
> >
> > For this purpose, mbuf->tx_metadata is moved as a separate new field and
> > renamed to 'metadata' to support both Rx and Tx metadata.
> >
> > For loopback/hairpin packet, metadata set on Rx/Tx may or may not be
> > propagated to the other path depending on HW capability.
> >
> > Signed-off-by: Yongseok Koh <yskoh@mellanox.com>
> 
> There is a mark on Rx which is delivered to application in hash.fdir.hi.
> Why do we need one more 32-bit value set by NIC and delivered to
> application?
> What is the difference between MARK and META on Rx?
> When application should use MARK and when META?
> Is there cases when both could be necessary?
> 
In my understanding, MARK is FDIR related thing, META seems to be NIC
specific. And we also need this kind of specific data field to export
NIC's data to application.

> Moreover, the third patch adds 32-bit tags which are not delivered to
> application. May be META/MARK should be simply a kind of TAG (e.g. with
> index 0 or marked using additional attribute) which is delivered to
> application?
> 
> (It is either API breakage (if tx_metadata is removed) or ABI breakage
> if metadata and tx_metadata will share new location after shinfo).
> 
Make use of udata64 to export NIC metadata to application ?
	RTE_STD_C11
	union {
		void *userdata;   /**< Can be used for external metadata */
		uint64_t udata64; /**< Allow 8-byte userdata on 32-bit */
		uint64_t rx_metadata;
	};
> Andrew.