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32 L2 Forwarding Sample Application with Cache Allocation Technology (CAT)
33 =======================================================================
35 Basic Forwarding sample application is a simple *skeleton* example of
36 a forwarding application. It has been extended to make use of CAT via extended
37 command line options and linking against the libpqos library.
39 It is intended as a demonstration of the basic components of a DPDK forwarding
40 application and use of the libpqos library to program CAT.
41 For more detailed implementations see the L2 and L3 forwarding
44 CAT and Code Data Prioritization (CDP) features allow management of the CPU's
45 last level cache. CAT introduces classes of service (COS) that are essentially
46 bitmasks. In current CAT implementations, a bit in a COS bitmask corresponds to
47 one cache way in last level cache.
48 A CPU core is always assigned to one of the CAT classes.
49 By programming CPU core assignment and COS bitmasks, applications can be given
50 exclusive, shared, or mixed access to the CPU's last level cache.
51 CDP extends CAT so that there are two bitmasks per COS,
52 one for data and one for code.
53 The number of classes and number of valid bits in a COS bitmask is CPU model
54 specific and COS bitmasks need to be contiguous. Sample code calls this bitmask
55 ``cbm`` or capacity bitmask.
56 By default, after reset, all CPU cores are assigned to COS 0 and all classes
57 are programmed to allow fill into all cache ways.
58 CDP is off by default.
60 For more information about CAT please see:
62 * https://github.com/01org/intel-cmt-cat
64 White paper demonstrating example use case:
66 * `Increasing Platform Determinism with Platform Quality of Service for the Data Plane Development Kit <http://www.intel.com/content/www/us/en/communications/increasing-platform-determinism-pqos-dpdk-white-paper.html>`_
68 Compiling the Application
69 -------------------------
72 Requires ``libpqos`` from Intel's
73 `intel-cmt-cat software package <https://github.com/01org/intel-cmt-cat>`_
74 hosted on GitHub repository. For installation notes, please see ``README`` file.
78 * https://github.com/01org/intel-cmt-cat
81 #. To compile the application export the path to PQoS lib
82 and the DPDK source tree and go to the example directory:
84 .. code-block:: console
86 export PQOS_INSTALL_PATH=/path/to/libpqos
89 To compile the sample application see :doc:`compiling`.
91 The application is located in the ``l2fwd-cat`` sub-directory.
94 Running the Application
95 -----------------------
97 To run the example in a ``linuxapp`` environment and enable CAT on cpus 0-2:
99 .. code-block:: console
101 ./build/l2fwd-cat -l 1 -n 4 -- --l3ca="0x3@(0-2)"
103 or to enable CAT and CDP on cpus 1,3:
105 .. code-block:: console
107 ./build/l2fwd-cat -l 1 -n 4 -- --l3ca="(0x00C00,0x00300)@(1,3)"
109 If CDP is not supported it will fail with following error message:
111 .. code-block:: console
113 PQOS: CDP requested but not supported.
114 PQOS: Requested CAT configuration is not valid!
115 PQOS: Shutting down PQoS library...
116 EAL: Error - exiting with code: 1
117 Cause: PQOS: L3CA init failed!
119 The option to enable CAT is:
121 * ``--l3ca='<common_cbm@cpus>[,<(code_cbm,data_cbm)@cpus>...]'``:
123 where ``cbm`` stands for capacity bitmask and must be expressed in
126 ``common_cbm`` is a single mask, for a CDP enabled system, a group of two
127 masks (``code_cbm`` and ``data_cbm``) is used.
129 ``(`` and ``)`` are necessary if it's a group.
131 ``cpus`` could be a single digit/range or a group and must be expressed in
134 ``(`` and ``)`` are necessary if it's a group.
136 e.g. ``--l3ca='0x00F00@(1,3),0x0FF00@(4-6),0xF0000@7'``
138 * cpus 1 and 3 share its 4 ways with cpus 4, 5 and 6;
140 * cpus 4, 5 and 6 share half (4 out of 8 ways) of its L3 with cpus 1 and 3;
142 * cpus 4, 5 and 6 have exclusive access to 4 out of 8 ways;
144 * cpu 7 has exclusive access to all of its 4 ways;
146 e.g. ``--l3ca='(0x00C00,0x00300)@(1,3)'`` for CDP enabled system
148 * cpus 1 and 3 have access to 2 ways for code and 2 ways for data, code and
149 data ways are not overlapping.
152 Refer to *DPDK Getting Started Guide* for general information on running
153 applications and the Environment Abstraction Layer (EAL) options.
156 To reset or list CAT configuration and control CDP please use ``pqos`` tool
158 `intel-cmt-cat software package <https://github.com/01org/intel-cmt-cat>`_.
160 To enabled or disable CDP:
162 .. code-block:: console
164 sudo ./pqos -S cdp-on
166 sudo ./pqos -S cdp-off
168 to reset CAT configuration:
170 .. code-block:: console
176 .. code-block:: console
180 For more info about ``pqos`` tool please see its man page or
181 `intel-cmt-cat wiki <https://github.com/01org/intel-cmt-cat/wiki>`_.
187 The following sections provide an explanation of the main components of the
190 All DPDK library functions used in the sample code are prefixed with ``rte_``
191 and are explained in detail in the *DPDK API Documentation*.
197 The ``main()`` function performs the initialization and calls the execution
198 threads for each lcore.
200 The first task is to initialize the Environment Abstraction Layer (EAL). The
201 ``argc`` and ``argv`` arguments are provided to the ``rte_eal_init()``
202 function. The value returned is the number of parsed arguments:
206 int ret = rte_eal_init(argc, argv);
208 rte_exit(EXIT_FAILURE, "Error with EAL initialization\n");
210 The next task is to initialize the PQoS library and configure CAT. The
211 ``argc`` and ``argv`` arguments are provided to the ``cat_init()``
212 function. The value returned is the number of parsed arguments:
216 int ret = cat_init(argc, argv);
218 rte_exit(EXIT_FAILURE, "PQOS: L3CA init failed!\n");
220 ``cat_init()`` is a wrapper function which parses the command, validates
221 the requested parameters and configures CAT accordingly.
223 Parsing of command line arguments is done in ``parse_args(...)``.
224 libpqos is then initialized with the ``pqos_init(...)`` call. Next, libpqos is
225 queried for system CPU information and L3CA capabilities via
226 ``pqos_cap_get(...)`` and ``pqos_cap_get_type(..., PQOS_CAP_TYPE_L3CA, ...)``
227 calls. When all capability and topology information is collected, the requested
228 CAT configuration is validated. A check is then performed (on per socket basis)
229 for a sufficient number of un-associated COS. COS are selected and
230 configured via the ``pqos_l3ca_set(...)`` call. Finally, COS are associated to
231 relevant CPUs via ``pqos_l3ca_assoc_set(...)`` calls.
233 ``atexit(...)`` is used to register ``cat_exit(...)`` to be called on
234 a clean exit. ``cat_exit(...)`` performs a simple CAT clean-up, by associating
235 COS 0 to all involved CPUs via ``pqos_l3ca_assoc_set(...)`` calls.