1.. BSD LICENSE 2 Copyright(c) 2010-2014 Intel Corporation. All rights reserved. 3 All rights reserved. 4 5 Redistribution and use in source and binary forms, with or without 6 modification, are permitted provided that the following conditions 7 are met: 8 9 * Redistributions of source code must retain the above copyright 10 notice, this list of conditions and the following disclaimer. 11 * Redistributions in binary form must reproduce the above copyright 12 notice, this list of conditions and the following disclaimer in 13 the documentation and/or other materials provided with the 14 distribution. 15 * Neither the name of Intel Corporation nor the names of its 16 contributors may be used to endorse or promote products derived 17 from this software without specific prior written permission. 18 19 THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS 20 "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT 21 LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR 22 A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT 23 OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, 24 SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT 25 LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, 26 DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY 27 THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT 28 (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE 29 OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. 30 31Packet Distributor Library 32========================== 33 34The DPDK Packet Distributor library is a library designed to be used for dynamic load balancing of traffic 35while supporting single packet at a time operation. 36When using this library, the logical cores in use are to be considered in two roles: firstly a distributor lcore, 37which is responsible for load balancing or distributing packets, 38and a set of worker lcores which are responsible for receiving the packets from the distributor and operating on them. 39The model of operation is shown in the diagram below. 40 41|packet_distributor1| 42 43Distributor Core Operation 44-------------------------- 45 46The distributor core does the majority of the processing for ensuring that packets are fairly shared among workers. 47The operation of the distributor is as follows: 48 49#. Packets are passed to the distributor component by having the distributor lcore thread call the "rte_distributor_process()" API 50 51#. 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. 52 The process API call will poll all the worker cache lines to see what workers are requesting packets. 53 54#. As workers request packets, the distributor takes packets from the set of packets passed in and distributes them to the workers. 55 As it does so, it examines the "tag" -- stored in the RSS hash field in the mbuf -- for each packet 56 and records what tags are being processed by each worker. 57 58#. If the next packet in the input set has a tag which is already being processed by a worker, 59 then that packet will be queued up for processing by that worker 60 and given to it in preference to other packets when that work next makes a request for work. 61 This ensures that no two packets with the same tag are processed in parallel, 62 and that all packets with the same tag are processed in input order. 63 64#. Once all input packets passed to the process API have either been distributed to workers 65 or been queued up for a worker which is processing a given tag, 66 then the process API returns to the caller. 67 68Other functions which are available to the distributor lcore are: 69 70* rte_distributor_returned_pkts() 71 72* rte_distributor_flush() 73 74* rte_distributor_clear_returns() 75 76Of these the most important API call is "rte_distributor_returned_pkts()" 77which should only be called on the lcore which also calls the process API. 78It returns to the caller all packets which have finished processing by all worker cores. 79Within this set of returned packets, all packets sharing the same tag will be returned in their original order. 80 81**NOTE:** 82If worker lcores buffer up packets internally for transmission in bulk afterwards, 83the packets sharing a tag will likely get out of order. 84Once a worker lcore requests a new packet, the distributor assumes that it has completely finished with the previous packet and 85therefore that additional packets with the same tag can safely be distributed to other workers -- 86who may then flush their buffered packets sooner and cause packets to get out of order. 87 88**NOTE:** 89No packet ordering guarantees are made about packets which do not share a common packet tag. 90 91Using the process and returned_pkts API, the following application workflow can be used, 92while allowing packet order within a packet flow -- identified by a tag -- to be maintained. 93 94.. image41_png has been renamed 95 96|packet_distributor2| 97 98The flush and clear_returns API calls, mentioned previously, 99are likely of less use that the process and returned_pkts APIS, and are principally provided to aid in unit testing of the library. 100Descriptions of these functions and their use can be found in the DPDK API Reference document. 101 102Worker Operation 103---------------- 104 105Worker cores are the cores which do the actual manipulation of the packets distributed by the packet distributor. 106Each worker calls "rte_distributor_get_pkt()" API to request a new packet when it has finished processing the previous one. 107[The previous packet should be returned to the distributor component by passing it as the final parameter to this API call.] 108 109Since it may be desirable to vary the number of worker cores, depending on the traffic load 110i.e. to save power at times of lighter load, 111it is possible to have a worker stop processing packets by calling "rte_distributor_return_pkt()" to indicate that 112it has finished the current packet and does not want a new one. 113 114.. |packet_distributor1| image:: img/packet_distributor1.png 115 116.. |packet_distributor2| image:: img/packet_distributor2.png 117
