[dpdk-dev] [PATCH] ethdev: extend flow metadata

Adrien Mazarguil adrien.mazarguil at 6wind.com
Mon Jul 29 17:06:05 CEST 2019


On Sun, Jul 14, 2019 at 02:46:58PM +0300, Andrew Rybchenko wrote:
> On 11.07.2019 10:44, Adrien Mazarguil wrote:
> > On Wed, Jul 10, 2019 at 04:37:46PM +0000, Yongseok Koh wrote:
> > > > On Jul 10, 2019, at 5:26 AM, Thomas Monjalon <thomas at monjalon.net> wrote:
> > > > 
> > > > 10/07/2019 14:01, Bruce Richardson:
> > > > > On Wed, Jul 10, 2019 at 12:07:43PM +0200, Olivier Matz wrote:
> > > > > > On Wed, Jul 10, 2019 at 10:55:34AM +0100, Bruce Richardson wrote:
> > > > > > > On Wed, Jul 10, 2019 at 11:31:56AM +0200, Olivier Matz wrote:
> > > > > > > > On Thu, Jul 04, 2019 at 04:21:22PM -0700, 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 at mellanox.com>
> > > > > > > > > --- a/lib/librte_mbuf/rte_mbuf.h
> > > > > > > > > +++ b/lib/librte_mbuf/rte_mbuf.h
> > > > > > > > > @@ -648,17 +653,6 @@ struct rte_mbuf {
> > > > > > > > > 			/**< User defined tags. See rte_distributor_process() */
> > > > > > > > > 			uint32_t usr;
> > > > > > > > > 		} hash;                   /**< hash information */
> > > > > > > > > -		struct {
> > > > > > > > > -			/**
> > > > > > > > > -			 * Application specific metadata value
> > > > > > > > > -			 * for egress flow rule match.
> > > > > > > > > -			 * Valid if PKT_TX_METADATA is set.
> > > > > > > > > -			 * Located here to allow conjunct use
> > > > > > > > > -			 * with hash.sched.hi.
> > > > > > > > > -			 */
> > > > > > > > > -			uint32_t tx_metadata;
> > > > > > > > > -			uint32_t reserved;
> > > > > > > > > -		};
> > > > > > > > > 	};
> > > > > > > > > 
> > > > > > > > > 	/** Outer VLAN TCI (CPU order), valid if PKT_RX_QINQ is set. */
> > > > > > > > > @@ -727,6 +721,11 @@ struct rte_mbuf {
> > > > > > > > > 	 */
> > > > > > > > > 	struct rte_mbuf_ext_shared_info *shinfo;
> > > > > > > > > 
> > > > > > > > > +	/** Application specific metadata value for flow rule match.
> > > > > > > > > +	 * Valid if PKT_RX_METADATA or PKT_TX_METADATA is set.
> > > > > > > > > +	 */
> > > > > > > > > +	uint32_t metadata;
> > > > > > > > > +
> > > > > > > > > } __rte_cache_aligned;
> > > > > > > > This will break the ABI, so we cannot put it in 19.08, and we need a
> > > > > > > > deprecation notice.
> > > > > > > > 
> > > > > > > Does it actually break the ABI? Adding a new field to the mbuf should only
> > > > > > > break the ABI if it either causes new fields to move or changes the
> > > > > > > structure size. Since this is at the end, it's not going to move any older
> > > > > > > fields, and since everything is cache-aligned I don't think the structure
> > > > > > > size changes either.
> > > > > > I think it does break the ABI: in previous version, when the PKT_TX_METADATA
> > > > > > flag is set, the associated value is put in m->tx_metadata (offset 44 on
> > > > > > x86-64), and in the next version, it will be in m->metadata (offset 112). So,
> > > > > > these 2 versions are not binary compatible.
> > > > > > 
> > > > > > Anyway, at least it breaks the API.
> > > > > Ok, I misunderstood. I thought it was the structure change itself you were
> > > > > saying broke the ABI. Yes, putting the data in a different place is indeed
> > > > > an ABI break.
> > > > We could add the new field and keep the old one unused,
> > > > so it does not break the ABI.
> > > Still breaks ABI if PKT_TX_METADATA is set. :-) In order not to break it, I can
> > > keep the current union'd field (tx_metadata) as is with PKT_TX_METADATA, add
> > > the new one at the end and make it used with the new PKT_RX_METADATA.
> > > 
> > > > However I suppose everybody will prefer a version using dynamic fields.
> > > > Is someone against using dynamic field for such usage?
> > > However, given that the amazing dynamic fields is coming soon (thanks for your
> > > effort, Olivier and Thomas!), I'd be honored to be the first user of it.
> > > 
> > > Olivier, I'll take a look at your RFC.
> > Just got a crazy idea while reading this thread... How about repurposing
> > that "reserved" field as "rx_metadata" in the meantime?
> 
> It overlaps with hash.fdir.hi which has RSS hash.

While it does overlap with hash.fdir.hi, isn't the RSS hash stored in the
"rss" field overlapping with hash.fdir.lo? (see struct rte_flow_action_rss)

hash.fdir.hi was originally used by FDIR and later repurposed by rte_flow
for its MARK action, which neatly qualifies as Rx metadata so renaming
"reserved" as "rx_metadata" could already make sense.

That is, assuming users do not need two different kinds of Rx metadata
returned simultaneously with their packets. I think it's safe.

> > I know reserved fields are cursed and no one's ever supposed to touch them
> > but this risk is mitigated by having the end user explicitly request its
> > use, so the patch author (and his relatives) should be safe from the
> > resulting bad juju.
> > 
> > Joke aside, while I like the idea of Tx/Rx META, I think the similarities
> > with MARK (and TAG eventually) is a problem. I wasn't available and couldn't
> > comment when META was originally added to the Tx path, but there's a lot of
> > overlap between these items/actions, without anything explaining to the end
> > user how and why they should pick one over the other, if they can be
> > combined at all and what happens in that case.
> > 
> > All this must be documented, then we should think about unifying their
> > respective features and deprecate the less capable items/actions. In my
> > opinion, users need exactly one method to mark/match some mark while
> > processing Rx/Tx traffic and *optionally* have that mark read from/written
> > to the mbuf, which may or may not be possible depending on HW features.

Thoughts regarding this suggestion? From a user perspective I think all
these actions should be unified but maybe there are good reasons to keep
them separate?

-- 
Adrien Mazarguil
6WIND


More information about the dev mailing list