doc: describe the SWX pipeline type

Add the new SWX pipeline type to the Programmer's Guide.

Signed-off-by: Cristian Dumitrescu <cristian.dumitrescu@intel.com>

diff --git a/doc/guides/prog_guide/packet_framework.rst b/doc/guides/prog_guide/packet_framework.rst
index 48d2575..3d4e3b6 100644 (file)
--- a/doc/guides/prog_guide/packet_framework.rst
+++ b/doc/guides/prog_guide/packet_framework.rst
@@ -1148,3 +1148,80 @@ Usually, to support a specific functional block, specific implementation of Pack
 with all the implementations sharing the same API: pure SW implementation (no acceleration), implementation using accelerator A, implementation using accelerator B, etc.
 The selection between these implementations could be done at build time or at run-time (recommended), based on which accelerators are present in the system,
 with no application changes required.
+
+The Software Switch (SWX) Pipeline
+----------------------------------
+
+The Software Switch (SWX) pipeline is designed to combine the DPDK performance with the flexibility of the P4-16 language [1]. It can be used either by itself
+to code a complete software switch or data plane application, or in combination with the open-source P4 compiler P4C [2], acting as a P4C back-end that allows
+the P4 programs to be translated to the DPDK SWX API and run on multi-core CPUs.
+
+The main features of the SWX pipeline are:
+
+*   Nothing is hard-wired, everything is dynamically defined: The packet headers (i.e. the network protocols), the packet meta-data, the actions, the tables
+    and the pipeline itself are dynamically defined instead of selected from a predefined set.
+
+*   Instructions: The actions and the life of the packet through the pipeline are defined with instructions that manipulate the pipeline objects mentioned
+    above. The pipeline is the main function of the packet program, with actions as subroutines triggered by the tables.
+
+*   Call external plugins: Extern objects and functions can be defined to call functionality that cannot be efficiently implemented with the existing
+    pipeline-oriented instruction set, such as: error detecting/correcting codes, cryptographic operations, meters, statistics counter arrays, heuristics, etc.
+
+*   Better control plane interaction: Transaction-oriented table update mechanism that supports multi-table atomic updates. Multiple tables can be updated in a
+    single step with only the before-update and the after-update table entries visible to the packets. Alignment with the P4Runtime [3] protocol.
+
+*   Performance: Multiple packets are in-flight within the pipeline at any moment. Each packet is owned by a different time-sharing thread in
+    run-to-completion, with the thread pausing before memory access operations such as packet I/O and table lookup to allow the memory prefetch to complete.
+    The instructions are verified and translated at initialization time with no run-time impact. The instructions are also optimized to detect and "fuse"
+    frequently used patterns into vector-like instructions transparently to the user.
+
+The main SWX pipeline components are:
+
+*   Input and output ports: Each port instantiates a port type that defines the port operations, e.g. Ethernet device port, PCAP port, etc. The RX interface
+    of the input ports and the TX interface of the output ports are single packet based, with packet batching typically implemented internally by each port for
+    performance reasons.
+
+*   Structure types: Each structure type is used to define the logical layout of a memory block, such as: packet headers, packet meta-data, action data stored
+    in a table entry, mailboxes of extern objects and functions. Similar to C language structs, each structure type is a well defined sequence of fields, with
+    each field having a unique name and a constant size.
+
+*   Packet headers: Each packet typically has one or multiple headers. The headers are extracted from the input packet as part of the packet parsing operation,
+    which is likely executed immediately after the packet reception. As result of the extract operation, each header is logically removed from the packet, so
+    once the packet parsing operation is completed, the input packet is reduced to opaque payload. Just before transmission, one or several headers are pushed
+    in front of each output packet through the emit operation; these headers can be part of the set of headers that were previously extracted from the input
+    packet (and potentially modified afterwards) or some new headers whose contents is generated by the pipeline (e.g. by reading them from tables). The format
+    of each packet header is defined by instantiating a structure type.
+
+*   Packet meta-data: The packet meta-data is filled in by the pipeline (e.g. by reading it from tables) or computed by the pipeline. It is not sent out unless
+    some of the meta-data fields are explicitly written into the headers emitted into the output packet. The format of the packet meta-data is defined by
+    instantiating a structure type.
+
+*   Extern objects and functions: Used to plug into the pipeline any functionality that cannot be efficiently implemented with the existing pipeline instruction
+    set. Each extern object and extern function has its own mailbox, which is used to pass the input arguments to and retrieve the output arguments from the
+    extern object member functions or the extern function.  The mailbox format is defined by instantiating a structure type.
+
+*   Instructions: The pipeline and its actions are defined with instructions from a predefined instruction set. The instructions are used to receive and
+    transmit the current packet, extract and emit headers from/into the packet, read/write the packet headers, packet meta-data and mailboxes, start table
+    lookup operations, read the action arguments from the table entry, call extern object member functions or extern functions. See the rte_swx_pipeline.h file
+    for the complete list of instructions.
+
+*   Actions: The pipeline actions are dynamically defined through instructions as opposed to predefined. Essentially, the actions are subroutines of the
+    pipeline program and their execution is triggered by the table lookup. The input arguments of each action are read from the table entry (in case of table
+    lookup hit) or the default table action (in case of table lookup miss) and are read-only; their format is defined by instantiating a structure type. The
+    actions have read-write access to the packet headers and meta-data.
+
+*   Table: Each pipeline typically has one or more lookup tables. The match fields of each table are flexibly selected from the packet headers and meta-data
+    defined for the current pipeline. The set of table actions is flexibly selected for each table from the set of actions defined for the current pipeline. The
+    tables can be looked at as special pipeline operators that result in one of the table actions being called, depending on the result of the table lookup
+    operation.
+
+*   Pipeline: The pipeline represents the main program that defines the life of the packet, with subroutines (actions) executed on table lookup. As packets
+    go through the pipeline, the packet headers and meta-data are transformed along the way.
+
+References:
+
+[1] P4-16 specification: https://p4.org/specs/
+
+[2] P4-16 compiler: https://github.com/p4lang/p4c
+
+[3] P4Runtime specification: https://p4.org/specs/