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+..  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.
+
+.. _Multi-process_Support:
+
+Multi-process Support
+=====================
+
+In the Intel® DPDK, multi-process support is designed to allow a group of Intel® DPDK processes
+to work together in a simple transparent manner to perform packet processing,
+or other workloads, on Intel® architecture hardware.
+To support this functionality,
+a number of additions have been made to the core Intel® DPDK Environment Abstraction Layer (EAL).
+
+The EAL has been modified to allow different types of Intel® DPDK processes to be spawned,
+each with different permissions on the hugepage memory used by the applications.
+For now, there are two types of process specified:
+
+*   primary processes, which can initialize and which have full permissions on shared memory
+
+*   secondary processes, which cannot initialize shared memory,
+    but can attach to pre- initialized shared memory and create objects in it.
+
+Standalone Intel® DPDK processes are primary processes,
+while secondary processes can only run alongside a primary process or
+after a primary process has already configured the hugepage shared memory for them.
+
+To support these two process types, and other multi-process setups described later,
+two additional command-line parameters are available to the EAL:
+
+*   --proc-type: for specifying a given process instance as the primary or secondary Intel® DPDK instance
+
+*   --file-prefix: to allow processes that do not want to co-operate to have different memory regions
+
+A number of example applications are provided that demonstrate how multiple Intel® DPDK processes can be used together.
+These are more fully documented in the "Multi- process Sample Application" chapter
+in the *Intel® DPDK Sample Application's User Guide*.
+
+Memory Sharing
+--------------
+
+The key element in getting a multi-process application working using the Intel® DPDK is to ensure that
+memory resources are properly shared among the processes making up the multi-process application.
+Once there are blocks of shared memory available that can be accessed by multiple processes,
+then issues such as inter-process communication (IPC) becomes much simpler.
+
+On application start-up in a primary or standalone process,
+the Intel DPDK records to memory-mapped files the details of the memory configuration it is using - hugepages in use,
+the virtual addresses they are mapped at, the number of memory channels present, etc.
+When a secondary process is started, these files are read and the EAL recreates the same memory configuration
+in the secondary process so that all memory zones are shared between processes and all pointers to that memory are valid,
+and point to the same objects, in both processes.
+
+.. note::
+
+    Refer to Section 23.3 "Multi-process Limitations" for details of
+    how Linux kernel Address-Space Layout Randomization (ASLR) can affect memory sharing.
+
+.. _pg_figure_16:
+
+**Figure 16. Memory Sharing in the Intel® DPDK Multi-process Sample Application**
+
+.. image42_png has been replaced
+
+|multi_process_memory|
+
+The EAL also supports an auto-detection mode (set by EAL --proc-type=auto flag ),
+whereby an Intel® DPDK process is started as a secondary instance if a primary instance is already running.
+
+Deployment Models
+-----------------
+
+Symmetric/Peer Processes
+~~~~~~~~~~~~~~~~~~~~~~~~
+
+Intel® DPDK multi-process support can be used to create a set of peer processes where each process performs the same workload.
+This model is equivalent to having multiple threads each running the same main-loop function,
+as is done in most of the supplied Intel® DPDK sample applications.
+In this model, the first of the processes spawned should be spawned using the --proc-type=primary EAL flag,
+while all subsequent instances should be spawned using the --proc-type=secondary flag.
+
+The simple_mp and symmetric_mp sample applications demonstrate this usage model.
+They are described in the "Multi-process Sample Application" chapter in the *Intel® DPDK Sample Application's User Guide*.
+
+Asymmetric/Non-Peer Processes
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+An alternative deployment model that can be used for multi-process applications
+is to have a single primary process instance that acts as a load-balancer or
+server distributing received packets among worker or client threads, which are run as secondary processes.
+In this case, extensive use of rte_ring objects is made, which are located in shared hugepage memory.
+
+The client_server_mp sample application shows this usage model.
+It is described in the "Multi-process Sample Application" chapter in the *Intel® DPDK Sample Application's User Guide*.
+
+Running Multiple Independent Intel® DPDK Applications
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+In addition to the above scenarios involving multiple Intel® DPDK processes working together,
+it is possible to run multiple Intel® DPDK processes side-by-side,
+where those processes are all working independently.
+Support for this usage scenario is provided using the --file-prefix parameter to the EAL.
+
+By default, the EAL creates hugepage files on each hugetlbfs filesystem using the rtemap_X filename,
+where X is in the range 0 to the maximum number of hugepages -1.
+Similarly, it creates shared configuration files, memory mapped in each process, using the /var/run/.rte_config filename,
+when run as root (or $HOME/.rte_config when run as a non-root user;
+if filesystem and device permissions are set up to allow this).
+The rte part of the filenames of each of the above is configurable using the file-prefix parameter.
+
+In addition to specifying the file-prefix parameter,
+any Intel® DPDK applications that are to be run side-by-side must explicitly limit their memory use.
+This is done by passing the -m flag to each process to specify how much hugepage memory, in megabytes,
+each process can use (or passing --socket-mem to specify how much hugepage memory on each socket each process can use).
+
+.. note::
+
+    Independent Intel® DPDK instances running side-by-side on a single machine cannot share any network ports.
+    Any network ports being used by one process should be blacklisted in every other process.
+
+Running Multiple Independent Groups of Intel® DPDK Applications
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+In the same way that it is possible to run independent Intel® DPDK applications side- by-side on a single system,
+this can be trivially extended to multi-process groups of Intel® DPDK applications running side-by-side.
+In this case, the secondary processes must use the same --file-prefix parameter
+as the primary process whose shared memory they are connecting to.
+
+.. note::
+
+    All restrictions and issues with multiple independent Intel®  DPDK processes running side-by-side
+    apply in this usage scenario also.
+
+Multi-process Limitations
+-------------------------
+
+There are a number of limitations to what can be done when running Intel® DPDK multi-process applications.
+Some of these are documented below:
+
+*   The multi-process feature requires that the exact same hugepage memory mappings be present in all applications.
+    The Linux security feature - Address-Space Layout Randomization (ASLR) can interfere with this mapping,
+    so it may be necessary to disable this feature in order to reliably run multi-process applications.
+
+.. warning::
+
+    Disabling Address-Space Layout Randomization (ASLR) may have security implications,
+    so it is recommended that it be disabled only when absolutely necessary,
+    and only when the implications of this change have been understood.
+
+*   All Intel® DPDK processes running as a single application and using shared memory must have distinct coremask arguments.
+    It is not possible to have a primary and secondary instance, or two secondary instances,
+    using any of the same logical cores.
+    Attempting to do so can cause corruption of memory pool caches, among other issues.
+
+*   The delivery of interrupts, such as Ethernet* device link status interrupts, do not work in secondary processes.
+    All interrupts are triggered inside the primary process only.
+    Any application needing interrupt notification in multiple processes should provide its own mechanism
+    to transfer the interrupt information from the primary process to any secondary process that needs the information.
+
+*   The use of function pointers between multiple processes running based of different compiled binaries is not supported,
+    since the location of a given function in one process may be different to its location in a second.
+    This prevents the librte_hash library from behaving properly as in a multi-threaded instance,
+    since it uses a pointer to the hash function internally.
+
+To work around this issue, it is recommended that multi-process applications perform the hash calculations by directly calling
+the hashing function from the code and then using the rte_hash_add_with_hash()/rte_hash_lookup_with_hash() functions
+instead of the functions which do the hashing internally, such as rte_hash_add()/rte_hash_lookup().
+
+*   Depending upon the hardware in use, and the number of Intel® DPDK processes used,
+    it may not be possible to have HPET timers available in each Intel® DPDK instance.
+    The minimum number of HPET comparators available to Linux* userspace can be just a single comparator,
+    which means that only the first, primary Intel® DPDK process instance can open and mmap  /dev/hpet.
+    If the number of required Intel® DPDK processes exceeds that of the number of available HPET comparators,
+    the TSC (which is the default timer in this release) must be used as a time source across all processes instead of the HPET.
+
+.. |multi_process_memory| image:: img/multi_process_memory.svg