--- /dev/null
+.. BSD LICENSE
+ Copyright(c) 2010-2014 Intel Corporation. All rights reserved.
+ All rights reserved.
+
+ Redistribution and use in source and binary forms, with or without
+ modification, are permitted provided that the following conditions
+ are met:
+
+ * Redistributions of source code must retain the above copyright
+ notice, this list of conditions and the following disclaimer.
+ * Redistributions in binary form must reproduce the above copyright
+ notice, this list of conditions and the following disclaimer in
+ the documentation and/or other materials provided with the
+ distribution.
+ * Neither the name of Intel Corporation nor the names of its
+ contributors may be used to endorse or promote products derived
+ from this software without specific prior written permission.
+
+ THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+ "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+ LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+ A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+ OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+ SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+ LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+ DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+ THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+ (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+ OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+
+Packet Distributor Library
+==========================
+
+The DPDK Packet Distributor library is a library designed to be used for dynamic load balancing of traffic
+while supporting single packet at a time operation.
+When using this library, the logical cores in use are to be considered in two roles: firstly a distributor lcore,
+which is responsible for load balancing or distributing packets,
+and a set of worker lcores which are responsible for receiving the packets from the distributor and operating on them.
+The model of operation is shown in the diagram below.
+
+.. figure:: img/packet_distributor1.*
+
+ Packet Distributor mode of operation
+
+
+Distributor Core Operation
+--------------------------
+
+The distributor core does the majority of the processing for ensuring that packets are fairly shared among workers.
+The operation of the distributor is as follows:
+
+#. Packets are passed to the distributor component by having the distributor lcore thread call the "rte_distributor_process()" API
+
+#. The worker lcores all share a single cache line with the distributor core in order to pass messages and packets to and from the worker.
+ The process API call will poll all the worker cache lines to see what workers are requesting packets.
+
+#. As workers request packets, the distributor takes packets from the set of packets passed in and distributes them to the workers.
+ As it does so, it examines the "tag" -- stored in the RSS hash field in the mbuf -- for each packet
+ and records what tags are being processed by each worker.
+
+#. If the next packet in the input set has a tag which is already being processed by a worker,
+ then that packet will be queued up for processing by that worker
+ and given to it in preference to other packets when that work next makes a request for work.
+ This ensures that no two packets with the same tag are processed in parallel,
+ and that all packets with the same tag are processed in input order.
+
+#. Once all input packets passed to the process API have either been distributed to workers
+ or been queued up for a worker which is processing a given tag,
+ then the process API returns to the caller.
+
+Other functions which are available to the distributor lcore are:
+
+* rte_distributor_returned_pkts()
+
+* rte_distributor_flush()
+
+* rte_distributor_clear_returns()
+
+Of these the most important API call is "rte_distributor_returned_pkts()"
+which should only be called on the lcore which also calls the process API.
+It returns to the caller all packets which have finished processing by all worker cores.
+Within this set of returned packets, all packets sharing the same tag will be returned in their original order.
+
+**NOTE:**
+If worker lcores buffer up packets internally for transmission in bulk afterwards,
+the packets sharing a tag will likely get out of order.
+Once a worker lcore requests a new packet, the distributor assumes that it has completely finished with the previous packet and
+therefore that additional packets with the same tag can safely be distributed to other workers --
+who may then flush their buffered packets sooner and cause packets to get out of order.
+
+**NOTE:**
+No packet ordering guarantees are made about packets which do not share a common packet tag.
+
+Using the process and returned_pkts API, the following application workflow can be used,
+while allowing packet order within a packet flow -- identified by a tag -- to be maintained.
+
+
+.. figure:: img/packet_distributor2.*
+
+ Application workflow
+
+
+The flush and clear_returns API calls, mentioned previously,
+are likely of less use that the process and returned_pkts APIS, and are principally provided to aid in unit testing of the library.
+Descriptions of these functions and their use can be found in the DPDK API Reference document.
+
+Worker Operation
+----------------
+
+Worker cores are the cores which do the actual manipulation of the packets distributed by the packet distributor.
+Each worker calls "rte_distributor_get_pkt()" API to request a new packet when it has finished processing the previous one.
+[The previous packet should be returned to the distributor component by passing it as the final parameter to this API call.]
+
+Since it may be desirable to vary the number of worker cores, depending on the traffic load
+i.e. to save power at times of lighter load,
+it is possible to have a worker stop processing packets by calling "rte_distributor_return_pkt()" to indicate that
+it has finished the current packet and does not want a new one.
Code Review / deb_dpdk.git / blobdiff