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

Andrew Rybchenko arybchenko at solarflare.com
Mon Jun 10 09:20:28 CEST 2019

On 6/10/19 6:19 AM, Wang, Haiyue wrote:
>> -----Original Message-----
>> From: dev [mailto:dev-bounces at dpdk.org] On Behalf Of Andrew Rybchenko
>> Sent: Sunday, June 9, 2019 22:24
>> To: Yongseok Koh <yskoh at mellanox.com>; shahafs at mellanox.com; thomas at monjalon.net; Yigit, Ferruh
>> <ferruh.yigit at intel.com>; adrien.mazarguil at 6wind.com; olivier.matz at 6wind.com
>> Cc: dev at 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.
>>> 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 at 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.

I think it is better to avoid NIC vendor-specifics in motivation. I 
that it exists for you, but I think it is better to look at it from RTE 
flow API
definition point of view: both are 32-bit (except endianess and I'm not sure
that I understand why meta is defined as big-endian since it is not a value
coming from or going to network in a packet, I'm sorry that I've missed it
on review that time), both may be set using action on Rx, both may be
matched using pattern item.

>> 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;
> 	};

As I understand it does not work for Tx and I'm not sure that it is
a good idea to have different locations for Tx and Rx.

RFC adds it at the end of mbuf, but it was rejected before since
it eats space in mbuf structure (CC Konstantin).

There is a long discussion on the topic before [1], [2], [3] and [4].


[1] http://mails.dpdk.org/archives/dev/2018-August/109660.html
[2] http://mails.dpdk.org/archives/dev/2018-September/111771.html
[3] http://mails.dpdk.org/archives/dev/2018-October/114559.html
[4] http://mails.dpdk.org/archives/dev/2018-October/115469.html

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