1 .. SPDX-License-Identifier: BSD-3-Clause
2 Copyright(c) 2016 Intel Corporation.
4 L2 Forwarding Sample Application with Cache Allocation Technology (CAT)
5 =======================================================================
7 Basic Forwarding sample application is a simple *skeleton* example of
8 a forwarding application. It has been extended to make use of CAT via extended
9 command line options and linking against the libpqos library.
11 It is intended as a demonstration of the basic components of a DPDK forwarding
12 application and use of the libpqos library to program CAT.
13 For more detailed implementations see the L2 and L3 forwarding
16 CAT and Code Data Prioritization (CDP) features allow management of the CPU's
17 last level cache. CAT introduces classes of service (COS) that are essentially
18 bitmasks. In current CAT implementations, a bit in a COS bitmask corresponds to
19 one cache way in last level cache.
20 A CPU core is always assigned to one of the CAT classes.
21 By programming CPU core assignment and COS bitmasks, applications can be given
22 exclusive, shared, or mixed access to the CPU's last level cache.
23 CDP extends CAT so that there are two bitmasks per COS,
24 one for data and one for code.
25 The number of classes and number of valid bits in a COS bitmask is CPU model
26 specific and COS bitmasks need to be contiguous. Sample code calls this bitmask
27 ``cbm`` or capacity bitmask.
28 By default, after reset, all CPU cores are assigned to COS 0 and all classes
29 are programmed to allow fill into all cache ways.
30 CDP is off by default.
32 For more information about CAT please see:
34 * https://github.com/01org/intel-cmt-cat
36 White paper demonstrating example use case:
38 * `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>`_
40 Compiling the Application
41 -------------------------
44 Requires ``libpqos`` from Intel's
45 `intel-cmt-cat software package <https://github.com/01org/intel-cmt-cat>`_
46 hosted on GitHub repository. For installation notes, please see ``README`` file.
50 * https://github.com/01org/intel-cmt-cat
53 #. To compile the application export the path to PQoS lib
54 and the DPDK source tree and go to the example directory:
56 .. code-block:: console
58 export PQOS_INSTALL_PATH=/path/to/libpqos
61 To compile the sample application see :doc:`compiling`.
63 The application is located in the ``l2fwd-cat`` sub-directory.
66 Running the Application
67 -----------------------
69 To run the example in a ``linux`` environment and enable CAT on cpus 0-2:
71 .. code-block:: console
73 ./<build_dir>/examples/dpdk-l2fwd-cat -l 1 -n 4 -- --l3ca="0x3@(0-2)"
75 or to enable CAT and CDP on cpus 1,3:
77 .. code-block:: console
79 ./<build_dir>/examples/dpdk-l2fwd-cat -l 1 -n 4 -- --l3ca="(0x00C00,0x00300)@(1,3)"
81 If CDP is not supported it will fail with following error message:
83 .. code-block:: console
85 PQOS: CDP requested but not supported.
86 PQOS: Requested CAT configuration is not valid!
87 PQOS: Shutting down PQoS library...
88 EAL: Error - exiting with code: 1
89 Cause: PQOS: L3CA init failed!
91 The option to enable CAT is:
93 * ``--l3ca='<common_cbm@cpus>[,<(code_cbm,data_cbm)@cpus>...]'``:
95 where ``cbm`` stands for capacity bitmask and must be expressed in
98 ``common_cbm`` is a single mask, for a CDP enabled system, a group of two
99 masks (``code_cbm`` and ``data_cbm``) is used.
101 ``(`` and ``)`` are necessary if it's a group.
103 ``cpus`` could be a single digit/range or a group and must be expressed in
106 ``(`` and ``)`` are necessary if it's a group.
108 e.g. ``--l3ca='0x00F00@(1,3),0x0FF00@(4-6),0xF0000@7'``
110 * cpus 1 and 3 share its 4 ways with cpus 4, 5 and 6;
112 * cpus 4, 5 and 6 share half (4 out of 8 ways) of its L3 with cpus 1 and 3;
114 * cpus 4, 5 and 6 have exclusive access to 4 out of 8 ways;
116 * cpu 7 has exclusive access to all of its 4 ways;
118 e.g. ``--l3ca='(0x00C00,0x00300)@(1,3)'`` for CDP enabled system
120 * cpus 1 and 3 have access to 2 ways for code and 2 ways for data, code and
121 data ways are not overlapping.
124 Refer to *DPDK Getting Started Guide* for general information on running
125 applications and the Environment Abstraction Layer (EAL) options.
128 To reset or list CAT configuration and control CDP please use ``pqos`` tool
130 `intel-cmt-cat software package <https://github.com/01org/intel-cmt-cat>`_.
132 To enabled or disable CDP:
134 .. code-block:: console
136 sudo ./pqos -S cdp-on
138 sudo ./pqos -S cdp-off
140 to reset CAT configuration:
142 .. code-block:: console
148 .. code-block:: console
152 For more info about ``pqos`` tool please see its man page or
153 `intel-cmt-cat wiki <https://github.com/01org/intel-cmt-cat/wiki>`_.
159 The following sections provide an explanation of the main components of the
162 All DPDK library functions used in the sample code are prefixed with ``rte_``
163 and are explained in detail in the *DPDK API Documentation*.
169 The ``main()`` function performs the initialization and calls the execution
170 threads for each lcore.
172 The first task is to initialize the Environment Abstraction Layer (EAL). The
173 ``argc`` and ``argv`` arguments are provided to the ``rte_eal_init()``
174 function. The value returned is the number of parsed arguments:
176 .. literalinclude:: ../../../examples/l2fwd-cat/l2fwd-cat.c
178 :start-after: Initialize the Environment Abstraction Layer (EAL). 8<
179 :end-before: >8 End of initializion the Environment Abstraction Layer (EAL).
182 The next task is to initialize the PQoS library and configure CAT. The
183 ``argc`` and ``argv`` arguments are provided to the ``cat_init()``
184 function. The value returned is the number of parsed arguments:
186 .. literalinclude:: ../../../examples/l2fwd-cat/l2fwd-cat.c
188 :start-after: Initialize the PQoS. 8<
189 :end-before: >8 End of initialization of PQoS.
192 ``cat_init()`` is a wrapper function which parses the command, validates
193 the requested parameters and configures CAT accordingly.
195 Parsing of command line arguments is done in ``parse_args(...)``.
196 libpqos is then initialized with the ``pqos_init(...)`` call. Next, libpqos is
197 queried for system CPU information and L3CA capabilities via
198 ``pqos_cap_get(...)`` and ``pqos_cap_get_type(..., PQOS_CAP_TYPE_L3CA, ...)``
199 calls. When all capability and topology information is collected, the requested
200 CAT configuration is validated. A check is then performed (on per socket basis)
201 for a sufficient number of un-associated COS. COS are selected and
202 configured via the ``pqos_l3ca_set(...)`` call. Finally, COS are associated to
203 relevant CPUs via ``pqos_l3ca_assoc_set(...)`` calls.
205 ``atexit(...)`` is used to register ``cat_exit(...)`` to be called on
206 a clean exit. ``cat_exit(...)`` performs a simple CAT clean-up, by associating
207 COS 0 to all involved CPUs via ``pqos_l3ca_assoc_set(...)`` calls.