--- /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.
+
+Thread Safety of DPDK Functions
+===============================
+
+The DPDK is comprised of several libraries.
+Some of the functions in these libraries can be safely called from multiple threads simultaneously, while others cannot.
+This section allows the developer to take these issues into account when building their own application.
+
+The run-time environment of the DPDK is typically a single thread per logical core.
+In some cases, it is not only multi-threaded, but multi-process.
+Typically, it is best to avoid sharing data structures between threads and/or processes where possible.
+Where this is not possible, then the execution blocks must access the data in a thread- safe manner.
+Mechanisms such as atomics or locking can be used that will allow execution blocks to operate serially.
+However, this can have an effect on the performance of the application.
+
+Fast-Path APIs
+--------------
+
+Applications operating in the data plane are performance sensitive but
+certain functions within those libraries may not be safe to call from multiple threads simultaneously.
+The hash, LPM and mempool libraries and RX/TX in the PMD are examples of this.
+
+The hash and LPM libraries are, by design, thread unsafe in order to maintain performance.
+However, if required the developer can add layers on top of these libraries to provide thread safety.
+Locking is not needed in all situations, and in both the hash and LPM libraries,
+lookups of values can be performed in parallel in multiple threads.
+Adding, removing or modifying values, however,
+cannot be done in multiple threads without using locking when a single hash or LPM table is accessed.
+Another alternative to locking would be to create multiple instances of these tables allowing each thread its own copy.
+
+The RX and TX of the PMD are the most critical aspects of a DPDK application
+and it is recommended that no locking be used as it will impact performance.
+Note, however, that these functions can safely be used from multiple threads
+when each thread is performing I/O on a different NIC queue.
+If multiple threads are to use the same hardware queue on the same NIC port,
+then locking, or some other form of mutual exclusion, is necessary.
+
+The ring library is based on a lockless ring-buffer algorithm that maintains its original design for thread safety.
+Moreover, it provides high performance for either multi- or single-consumer/producer enqueue/dequeue operations.
+The mempool library is based on the DPDK lockless ring library and therefore is also multi-thread safe.
+
+Performance Insensitive API
+---------------------------
+
+Outside of the performance sensitive areas described in Section 25.1,
+the DPDK provides a thread-safe API for most other libraries.
+For example, malloc and memzone functions are safe for use in multi-threaded and multi-process environments.
+
+The setup and configuration of the PMD is not performance sensitive, but is not thread safe either.
+It is possible that the multiple read/writes during PMD setup and configuration could be corrupted in a multi-thread environment.
+Since this is not performance sensitive, the developer can choose to add their own layer to provide thread-safe setup and configuration.
+It is expected that, in most applications, the initial configuration of the network ports would be done by a single thread at startup.
+
+Library Initialization
+----------------------
+
+It is recommended that DPDK libraries are initialized in the main thread at application startup
+rather than subsequently in the forwarding threads.
+However, the DPDK performs checks to ensure that libraries are only initialized once.
+If initialization is attempted more than once, an error is returned.
+
+In the multi-process case, the configuration information of shared memory will only be initialized by the master process.
+Thereafter, both master and secondary processes can allocate/release any objects of memory that finally rely on rte_malloc or memzones.
+
+Interrupt Thread
+----------------
+
+The DPDK works almost entirely in Linux user space in polling mode.
+For certain infrequent operations, such as receiving a PMD link status change notification,
+callbacks may be called in an additional thread outside the main DPDK processing threads.
+These function callbacks should avoid manipulating DPDK objects that are also managed by the normal DPDK threads,
+and if they need to do so,
+it is up to the application to provide the appropriate locking or mutual exclusion restrictions around those objects.
Code Review / deb_dpdk.git / blobdiff