[dpdk-dev] [PATCH v4] ethdev: extend flow metadata

[Slava Ovsiienko]

> -----Original Message-----
> From: Andrew Rybchenko <arybchenko at solarflare.com>
> Sent: Wednesday, October 30, 2019 9:35
> To: Slava Ovsiienko <viacheslavo at mellanox.com>; Thomas Monjalon
> <thomas at monjalon.net>; olivier.matz at 6wind.com
> Cc: dev at dpdk.org; Matan Azrad <matan at mellanox.com>; Ori Kam
> <orika at mellanox.com>; Yongseok Koh <yskoh at mellanox.com>
> Subject: Re: [dpdk-dev] [PATCH v4] ethdev: extend flow metadata
> 
> @Olivier, please, take a look at the end of the mail.
> 
> On 10/29/19 8:19 PM, Slava Ovsiienko wrote:
> > Hi, Andrew
> >
> > Thank you for the review.
> >
> >> -----Original Message-----
> >> From: Andrew Rybchenko <arybchenko at solarflare.com>
> >> Sent: Tuesday, October 29, 2019 18:22
> >> To: Slava Ovsiienko <viacheslavo at mellanox.com>; dev at dpdk.org
> >> Cc: Thomas Monjalon <thomas at monjalon.net>; Matan Azrad
> >> <matan at mellanox.com>; olivier.matz at 6wind.com; Ori Kam
> >> <orika at mellanox.com>; Yongseok Koh <yskoh at mellanox.com>
> >> Subject: Re: [dpdk-dev] [PATCH v4] ethdev: extend flow metadata
> >>
> >> On 10/27/19 9:40 PM, Viacheslav Ovsiienko wrote:
> >>> Currently, metadata can be set on egress path via mbuf tx_metadata
> >>> field with PKT_TX_METADATA flag and RTE_FLOW_ITEM_TYPE_META
> >> matches metadata.
> >>> This patch extends the metadata feature 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 ingress. 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
> >>> metadata dynamic field of mbuf which can be accessed by
> >> RTE_FLOW_DYNF_METADATA().
> >>> PKT_RX_DYNF_METADATA flag will be set along with the data.
> >>>
> >>> The mbuf dynamic field must be registered by calling
> >>> rte_flow_dynf_metadata_register() prior to use SET_META action.
> >>>
> >>> The availability of dynamic mbuf metadata field can be checked with
> >>> rte_flow_dynf_metadata_avail() routine.
> >>>
> >>> For loopback/hairpin packet, metadata set on Rx/Tx may or may not be
> >>> propagated to the other path depending on hardware capability.
> >>>
> >>> Signed-off-by: Yongseok Koh <yskoh at mellanox.com>
> >>> Signed-off-by: Viacheslav Ovsiienko <viacheslavo at mellanox.com>
> >> Above explanations lack information about "meta" vs "mark" which may
> >> be set on Rx as well and delivered in other mbuf field.
> >> It should be explained by one more field is required and rules defined.
> > There is some story about metadata features.
> > Initially, there were proposed two metadata related actions:
> >
> > - RTE_FLOW_ACTION_TYPE_FLAG
> > - RTE_FLOW_ACTION_TYPE_MARK
> >
> > These actions set the special flag in the packet metadata, MARK action
> > stores some specified value in the metadata storage, and, on the
> > packet receiving PMD puts the flag and value to the mbuf and
> > applications can see the packet was threated inside flow engine
> > according to the appropriate RTE flow(s). MARK and FLAG are like some
> > kind of gateway to transfer some per-packet information from the flow
> engine to the application via receiving datapath.
> >
> >  From the datapath point of view, the MARK and FLAG are related to the
> receiving side only.
> > It would useful to have the same gateway on the transmitting side and
> > there was the feature of type RTE_FLOW_ITEM_TYPE_META was
> proposed.
> > The application can fill the field in mbuf and this value will be transferred to
> some field in the packet metadata inside the flow engine.
> > It did not matter whether these metadata fields are shared because of
> > MARK and META items belonged to different domains (receiving and
> transmitting) and could be vendor-specific.
> >
> > So far, so good, DPDK proposes some entities to control metadata
> > inside the flow engine and gateways to exchange these values on a per-
> packet basis via datapaths.
> >
> > As we can see, the MARK and META means are not symmetric, there is
> > absent action which would allow us to set META value on the transmitting
> path. So, the action of type:
> > - RTE_FLOW_ACTION_TYPE_SET_META is proposed.
> >
> > The next, applications raise the new requirements for packet metadata.
> > The flow engines are getting more complex, internal switches are
> > introduced, multiple ports might be supported within the same flow
> > engine namespace. From the DPDK points of view, it means the packets
> > might be sent on one eth_dev port and received on the other one, and the
> packet path inside the flow engine entirely belongs to the same hardware
> device. The simplest example is SR-IOV with PF, VFs and the representors.
> > And there is a brilliant opportunity to provide some out-of-band channel to
> transfer some extra data
> >   from one port to another one, besides the packet data itself.
> >
> >
> >> Above explanations lack information about "meta" vs "mark" which may
> >> be set on Rx as well and delivered in other mbuf field.
> >> It should be explained by one more field is required and rules defined.
> >> Otherwise we can endup in half PMDs supporting mark only, half PMDs
> >> supporting meta only and applications in an interesting situation to
> >> make a choice which one to use.
> > There is no "mark" vs "meta". MARK and META means are kept for
> > compatibility issues and legacy part works exactly as before. The
> > trials (with flow_validate)  is supposed to check whether PMD supports
> > MARK or META feature on appropriate domain. It depends on PMD
> > implementation, configuration and underlaying HW/FW/kernel capabilities
> and should be resolved in runtime.
> 
> The trials a way, but very tricky way. My imagination draws me pictures how
> an application code could look like in attempt to use either mark or meta for
> Rx only and these pictures are not nice.
Agree, trials is not the best way.
For now there is no application trying to choose mark or meta, because these ones
belonged to other domains, and extension is newly introduced. 
So, the applications using mark will continue use mark, the same is regarding meta.
The new application definitely will ask for both mark and of them,
we have the requirements from customers  - "give us as many through bits as you can".
This new application just may refuse to work if metadata features are not detected,
because relays on it strongly.
BTW, trials are not so complex: rte_flow_validate(mark), rte_flow_validate_metadata()
and that's it.

> May be it will look acceptable when mark becomes a dynamic since usage of
> either one or another dynamic field is definitely easier than usage of either
> fixed or dynamic field.
At least in PMD datapath it does not look very ugly.
> 
> May be dynamic field for mark at fixed offset should be introduced in the
> release or the nearest future? It will allow to preserve ABI up to 20.11 and
> provide future proof API.
> The trick is to register dynamic meta field at fixed offset at start of a day to
> be sure that it is guaranteed to succeed.
> It sounds like it is a transition mechanism from fixed to dynamic fields.
> 
> [snip]
> 
> >>> diff --git a/lib/librte_ethdev/rte_flow.h
> >>> b/lib/librte_ethdev/rte_flow.h index 4fee105..b821557 100644
> >>> --- a/lib/librte_ethdev/rte_flow.h
> >>> +++ b/lib/librte_ethdev/rte_flow.h
> >>> @@ -28,6 +28,8 @@
> >>>    #include <rte_byteorder.h>
> >>>    #include <rte_esp.h>
> >>>    #include <rte_higig.h>
> >>> +#include <rte_mbuf.h>
> >>> +#include <rte_mbuf_dyn.h>
> >>>
> >>>    #ifdef __cplusplus
> >>>    extern "C" {
> >>> @@ -418,7 +420,8 @@ enum rte_flow_item_type {
> >>>    	/**
> >>>    	 * [META]
> >>>    	 *
> >>> -	 * Matches a metadata value specified in mbuf metadata field.
> >>> +	 * Matches a metadata value.
> >>> +	 *
> >>>    	 * See struct rte_flow_item_meta.
> >>>    	 */
> >>>    	RTE_FLOW_ITEM_TYPE_META,
> >>> @@ -1263,9 +1266,17 @@ struct rte_flow_item_icmp6_nd_opt_tla_eth
> {
> >>>    #endif
> >>>
> >>>    /**
> >>> - * RTE_FLOW_ITEM_TYPE_META.
> >>> + * @warning
> >>> + * @b EXPERIMENTAL: this structure may change without prior notice
> >> Is it allowed to make experimental back?
> > I think we should remove EXPERIMENTAL here. We do not introduce new
> > feature, but just extend the apply area.
> 
> Agreed.
> 
> >>>     *
> >>> - * Matches a specified metadata value.
> >>> + * RTE_FLOW_ITEM_TYPE_META
> >>> + *
> >>> + * Matches a specified metadata value. On egress, metadata can be
> >>> + set either by
> >>> + * mbuf tx_metadata field with PKT_TX_METADATA flag or
> >>> + * RTE_FLOW_ACTION_TYPE_SET_META. On ingress,
> >>> + RTE_FLOW_ACTION_TYPE_SET_META sets
> >>> + * metadata for a packet and the metadata will be reported via mbuf
> >>> + metadata
> >>> + * dynamic field with PKT_RX_DYNF_METADATA flag. The dynamic
> mbuf
> >>> + field must be
> >>> + * registered in advance by rte_flow_dynf_metadata_register().
> >>>     */
> >>>    struct rte_flow_item_meta {
> >>>    	rte_be32_t data;
> >> [snip]
> >>
> >>> @@ -2429,6 +2447,55 @@ struct rte_flow_action_set_mac {
> >>>    	uint8_t mac_addr[RTE_ETHER_ADDR_LEN];
> >>>    };
> >>>
> >>> +/**
> >>> + * @warning
> >>> + * @b EXPERIMENTAL: this structure may change without prior notice
> >>> + *
> >>> + * RTE_FLOW_ACTION_TYPE_SET_META
> >>> + *
> >>> + * Set metadata. Metadata set by mbuf tx_metadata field with
> >>> + * PKT_TX_METADATA flag on egress will be overridden by this action.
> >>> +On
> >>> + * ingress, the metadata will be carried by mbuf metadata dynamic
> >>> +field
> >>> + * with PKT_RX_DYNF_METADATA flag if set.  The dynamic mbuf field
> >>> +must be
> >>> + * registered in advance by rte_flow_dynf_metadata_register().
> >>> + *
> >>> + * Altering partial bits is supported with mask. For bits which
> >>> +have never
> >>> + * been set, unpredictable value will be seen depending on driver
> >>> + * implementation. For loopback/hairpin packet, metadata set on
> >>> +Rx/Tx may
> >>> + * or may not be propagated to the other path depending on HW
> >> capability.
> >>> + *
> >>> + * RTE_FLOW_ITEM_TYPE_META matches metadata.
> >>> + */
> >>> +struct rte_flow_action_set_meta {
> >>> +	rte_be32_t data;
> >>> +	rte_be32_t mask;
> >> As I understand tx_metadata is host endian. Just double-checking.
> >> Is a new dynamic field host endian or big endian?
> >> I definitely would like to see motivation in comments why data/mask
> >> are big- endian here.
> > metadata is opaque value, endianness does not matter, there are no
> > some special motivations for choosing endiannes. rte_flow_item_meta()
> > structure provides data with rte_be32_t type, so meta related action does
> the same.
> 
> Endianness of meta in mbuf and flow API should match and it must be
Yes, and they match (for meta), both are rte_be32_t. OK, will emphasize it in docs.

> documented. Endianness is important if a HW supports less bits since it
> makes a hit for application to use LSB first if the bit space is sufficient.
> mark is defined as host-endian (uint32_t) and I think meta should be the
> same. Otherwise it complicates even more either mark or meta usage as
> discussed above .
mark is mark, meta is meta, these ones are not interrelated (despite they
are becoming similar). And there is no choice between mark and meta.
It is not obvious we should have the same endianness for both.
There are some applications using this legacy features, so there might be compatibility
issues either.

> 
> Yes, I think that rte_flow_item_meta should be fixed since both mark and
> tx_metadata are host-endian.
> 
> (it says nothing about HW interface which is vendor specific and vendor
> PMDs should care about it)
Handling this in PMD might introduce the extra endianness conversion in datapath,
impacting performance. Not nice, IMO.
> 
> > I could assume the origin of selecting bigendian type was the
> > endianness of metadata field in Tx descriptor of ConnectX NICs.
> >
> >>> +};
> >>> +
> >>> +/* Mbuf dynamic field offset for metadata. */ extern int
> >>> +rte_flow_dynf_metadata_offs;
> >>> +
> >>> +/* Mbuf dynamic field flag mask for metadata. */ extern uint64_t
> >>> +rte_flow_dynf_metadata_mask;
> >> These two global variables look frightening to me.
> >> It does not look good to me.
> > For me too. But we need the performance, these ones are intended for
> > usage in datapath, any overhead is painful.
> 
> @Olivier, could you share your thoughts, please.
> 
> Andrew.

With best regards, Slava