[dpdk-dev] [RFC v2] Flow classification library

[Adrien Mazarguil]

On Mon, May 22, 2017 at 02:53:28PM +0100, Ferruh Yigit wrote:
> On 5/19/2017 5:30 PM, Iremonger, Bernard wrote:
> > Hi Ferruh,
> > 
> >> -----Original Message-----
> >> From: dev [mailto:dev-bounces at dpdk.org] On Behalf Of Ferruh Yigit
> >> Sent: Thursday, May 18, 2017 7:12 PM
> >> To: dev at dpdk.org
> >> Cc: Yigit, Ferruh <ferruh.yigit at intel.com>; Mcnamara, John
> >> <john.mcnamara at intel.com>; Tahhan, Maryam
> >> <maryam.tahhan at intel.com>
> >> Subject: [dpdk-dev] [RFC v2] Flow classification library
> >>
> >> DPDK works with packets, but some network administration tools works
> >> based on flow information.
> >>
> >> This library is suggested to provide helper API to convert packet based
> >> information to the flow records.
> >>
> >> Basically the library consist of a single API that gets packets, flow definition
> >> and action as parameter and provides flow stats based on action. Application
> >> should call the API for all received packets.
> >>
> >> Library header file has more comments on how library works and provided
> >> APIs.
> >>
> >> Packets to flow conversion will cause performance drop, that is why
> >> conversion done on demand by an API call provided by this library.
> >>
> >> Initial implementation in mind is to provide support for IPFIX metering
> >> process but library planned to be as generic as possible. And flow information
> >> provided by this library is missing to implement full IPFIX features, but this is
> >> planned to be initial step.
> >>
> >> Flows are defined using rte_flow, also measurements (actions) are provided
> >> by rte_flow. To support more IPFIX measurements, the implementation may
> >> require extending rte_flow addition to implementing this library.
> > 
> > Do you know what extensions are needed to the rte_flow code?
> 
> The extension may be required on two fields:
> 1- Defining the flow
> 2- Available actions
> 
> For defining the flow, an update may not be required, specially at first
> version of the library.
> 
> But for action, there may be some updates.
> 
> IPFIX RFC defines Metering process as [1], (in [2]). This library should
> provide helper APIs to metering process.
> 
> Currently only action can be used in rte_flow is COUNT, more actions can
> be added to help "packet header capturing, timestamping, sampling,
> classifying" tasks of the metering process.
> 
> The exact list depends on the what will be implemented in this release.
> 
> 
> [1]
>    Metering Process
> 
>       The Metering Process generates Flow Records.  Inputs to the
>       process are packet headers, characteristics, and Packet Treatment
>       observed at one or more Observation Points.
> 
>       The Metering Process consists of a set of functions that includes
>       packet header capturing, timestamping, sampling, classifying, and
>       maintaining Flow Records.
> 
>       The maintenance of Flow Records may include creating new records,
>       updating existing ones, computing Flow statistics, deriving
>       further Flow properties, detecting Flow expiration, passing Flow
>       Records to the Exporting Process, and deleting Flow Records.
> 
> [2]
> https://tools.ietf.org/html/rfc7011

Since I did not take this into account in my previous answer [3], I now
understand several of these requirements cannot be met by hardware (at least
in the near future). Therefore I think it makes sense to leave IPFIX and
more generally the maintenance of software data associated with flows to
separate libraries, instead of adding many new rte_flow actions that can
only be implemented in software.

A hybrid solution as described in [3] is still needed regardless to offload
flow recognition, so that only flows of interest are reprocessed in software
to compute IPFIX and other data.

You suggested at one point to take flow rules in addition to mbufs as input
to handle that. Well, that's actually a nice approach.

For this to work, rte_flow_classify would have to use opaque handles like
rte_flow, provided back by the application when attempting to classify
traffic. If the handle is not known (e.g. MARK is unsupported), a separate
API function could take a mbuf as input and spit the related
rte_flow_classify object if any.

To be clear:

1. Create classifier object:

   classify = rte_flow_classify_create([some rte_flow pattern],
      [classify-specific actions list, associated resources]);

2. Create some flow rule with a MARK action to identify it uniquely. This
   step might fail and flow can be NULL, that's not an issue:

   flow = rte_flow_create([the same pattern], MARK with id 42)

3. For each received packet:

   /*
    * Attempt HW and fall back on SW for flow identification in order to
    * update classifier flow-related data.
    */
   if (flow) {
      if (mbuf->ol_flags & PKT_RX_FDIR_ID && mbuf->hash.fdir.hi == 42)
         tmp_classify = classify;
   } else {
      tmp_classify = rte_flow_classify_lookup([classifier candidates], mbuf);
   }
   if (tmp_classify)
         rte_flow_classify_update(tmp_classify, mbuf);

4. At some point, retrieve computed data from the classifier object itself:

   rte_flow_classify_stats_get(classify, [output buffer(s)])

On the RX path, the MARK action can be enough to implement the above. When
not supported, it could also be emulated through the "sw_fallback" bit
described in [3] however if the above approach is fine, no need for that.

It's a bit more complicated to benefit from rte_flow on the TX path since no
MARK data can be returned. There is currently no other solution than doing
it all in software anyway.

[3] http://dpdk.org/ml/archives/dev/2017-May/066177.html

-- 
Adrien Mazarguil
6WIND