-.. 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.
+.. SPDX-License-Identifier: BSD-3-Clause
+ Copyright(c) 2010-2014 Intel Corporation.
.. _Multi-process_Support:
Multi-process Support
=====================
-In the Intel® DPDK, multi-process support is designed to allow a group of Intel® DPDK processes
+In the DPDK, multi-process support is designed to allow a group of DPDK processes
to work together in a simple transparent manner to perform packet processing,
-or other workloads, on Intel® architecture hardware.
+or other workloads.
To support this functionality,
-a number of additions have been made to the core Intel® DPDK Environment Abstraction Layer (EAL).
+a number of additions have been made to the core DPDK Environment Abstraction Layer (EAL).
-The EAL has been modified to allow different types of Intel® DPDK processes to be spawned,
+The EAL has been modified to allow different types of 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:
* 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,
+Standalone 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.
+.. note::
+
+ Secondary processes should run alongside primary process with same DPDK version.
+
+ Secondary processes which requires access to physical devices in Primary process, must
+ be passed with the same whitelist and blacklist options.
+
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
+* ``--proc-type:`` for specifying a given process instance as the primary or secondary DPDK instance
-* --file-prefix: to allow processes that do not want to co-operate to have different memory regions
+* ``--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.
+A number of example applications are provided that demonstrate how multiple 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*.
+in the *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
+The key element in getting a multi-process application working using the 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 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,
.. note::
- Refer to Section 23.3 "Multi-process Limitations" for details of
+ Refer to `Multi-process Limitations`_ for details of
how Linux kernel Address-Space Layout Randomization (ASLR) can affect memory sharing.
-.. _pg_figure_16:
+ If the primary process was run with ``--legacy-mem`` or
+ ``--single-file-segments`` switch, secondary processes must be run with the
+ same switch specified. Otherwise, memory corruption may occur.
+
+.. _figure_multi_process_memory:
-**Figure 16. Memory Sharing in the Intel® DPDK Multi-process Sample Application**
+.. figure:: img/multi_process_memory.*
-.. image42_png has been replaced
+ Memory Sharing in the DPDK Multi-process Sample Application
-|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.
+The EAL also supports an auto-detection mode (set by EAL ``--proc-type=auto`` flag ),
+whereby an 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.
+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.
+as is done in most of the supplied 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*.
+They are described in the "Multi-process Sample Application" chapter in the *DPDK Sample Application's User Guide*.
Asymmetric/Non-Peer 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*.
+It is described in the "Multi-process Sample Application" chapter in the *DPDK Sample Application's User Guide*.
-Running Multiple Independent Intel® DPDK Applications
-~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+Running Multiple Independent 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,
+In addition to the above scenarios involving multiple DPDK processes working together,
+it is possible to run multiple 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.
+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.
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).
+any DPDK applications that are to be run side-by-side must explicitly limit their memory use.
+This is less of a problem on Linux, as by default, applications will not
+allocate more memory than they need. However if ``--legacy-mem`` is used, DPDK
+will attempt to preallocate all memory it can get to, and memory use must be
+explicitly limited. 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.
+ Independent 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
-~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+Running Multiple Independent Groups of 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
+In the same way that it is possible to run independent DPDK applications side- by-side on a single system,
+this can be trivially extended to multi-process groups of 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
+ All restrictions and issues with multiple independent 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.
+There are a number of limitations to what can be done when running 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.
+ This makes secondary process startup process generally unreliable. Disabling
+ Linux security feature - Address-Space Layout Randomization (ASLR) may
+ help getting more consistent mappings, but not necessarily more reliable -
+ if the mappings are wrong, they will be consistently wrong!
.. warning::
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.
+* All DPDK processes running as a single application and using shared memory must have distinct coremask/corelist 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 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.
+* Depending upon the hardware in use, and the number of DPDK processes used,
+ it may not be possible to have HPET timers available in each 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,
+ which means that only the first, primary DPDK process instance can open and mmap /dev/hpet.
+ If the number of required 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
+Communication between multiple processes
+----------------------------------------
+
+While there are multiple ways one can approach inter-process communication in
+DPDK, there is also a native DPDK IPC API available. It is not intended to be
+performance-critical, but rather is intended to be a convenient, general
+purpose API to exchange short messages between primary and secondary processes.
+
+DPDK IPC API supports the following communication modes:
+
+* Unicast message from secondary to primary
+* Broadcast message from primary to all secondaries
+
+In other words, any IPC message sent in a primary process will be delivered to
+all secondaries, while any IPC message sent in a secondary process will only be
+delivered to primary process. Unicast from primary to secondary or from
+secondary to secondary is not supported.
+
+There are three types of communications that are available within DPDK IPC API:
+
+* Message
+* Synchronous request
+* Asynchronous request
+
+A "message" type does not expect a response and is meant to be a best-effort
+notification mechanism, while the two types of "requests" are meant to be a two
+way communication mechanism, with the requester expecting a response from the
+other side.
+
+Both messages and requests will trigger a named callback on the receiver side.
+These callbacks will be called from within a dedicated IPC or interrupt thread
+that are not part of EAL lcore threads.
+
+Registering for incoming messages
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+Before any messages can be received, a callback will need to be registered.
+This is accomplished by calling ``rte_mp_action_register()`` function. This
+function accepts a unique callback name, and a function pointer to a callback
+that will be called when a message or a request matching this callback name
+arrives.
+
+If the application is no longer willing to receive messages intended for a
+specific callback function, ``rte_mp_action_unregister()`` function can be
+called to ensure that callback will not be triggered again.
+
+Sending messages
+~~~~~~~~~~~~~~~~
+
+To send a message, a ``rte_mp_msg`` descriptor must be populated first. The list
+of fields to be populated are as follows:
+
+* ``name`` - message name. This name must match receivers' callback name.
+* ``param`` - message data (up to 256 bytes).
+* ``len_param`` - length of message data.
+* ``fds`` - file descriptors to pass long with the data (up to 8 fd's).
+* ``num_fds`` - number of file descriptors to send.
+
+Once the structure is populated, calling ``rte_mp_sendmsg()`` will send the
+descriptor either to all secondary processes (if sent from primary process), or
+to primary process (if sent from secondary process). The function will return
+a value indicating whether sending the message succeeded or not.
+
+Sending requests
+~~~~~~~~~~~~~~~~
+
+Sending requests involves waiting for the other side to reply, so they can block
+for a relatively long time.
+
+To send a request, a message descriptor ``rte_mp_msg`` must be populated.
+Additionally, a ``timespec`` value must be specified as a timeout, after which
+IPC will stop waiting and return.
+
+For synchronous synchronous requests, the ``rte_mp_reply`` descriptor must also
+be created. This is where the responses will be stored. The list of fields that
+will be populated by IPC are as follows:
+
+* ``nb_sent`` - number indicating how many requests were sent (i.e. how many
+ peer processes were active at the time of the request).
+* ``nb_received`` - number indicating how many responses were received (i.e. of
+ those peer processes that were active at the time of request, how many have
+ replied)
+* ``msgs`` - pointer to where all of the responses are stored. The order in
+ which responses appear is undefined. When doing synchronous requests, this
+ memory must be freed by the requestor after request completes!
+
+For asynchronous requests, a function pointer to the callback function must be
+provided instead. This callback will be called when the request either has timed
+out, or will have received a response to all the messages that were sent.
+
+.. warning::
+
+ When an asynchronous request times out, the callback will be called not by
+ a dedicated IPC thread, but rather from EAL interrupt thread. Because of
+ this, it may not be possible for DPDK to trigger another interrupt-based
+ event (such as an alarm) while handling asynchronous IPC callback.
+
+When the callback is called, the original request descriptor will be provided
+(so that it would be possible to determine for which sent message this is a
+callback to), along with a response descriptor like the one described above.
+When doing asynchronous requests, there is no need to free the resulting
+``rte_mp_reply`` descriptor.
+
+Receiving and responding to messages
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+To receive a message, a name callback must be registered using the
+``rte_mp_action_register()`` function. The name of the callback must match the
+``name`` field in sender's ``rte_mp_msg`` message descriptor in order for this
+message to be delivered and for the callback to be trigger.
+
+The callback's definition is ``rte_mp_t``, and consists of the incoming message
+pointer ``msg``, and an opaque pointer ``peer``. Contents of ``msg`` will be
+identical to ones sent by the sender.
+
+If a response is required, a new ``rte_mp_msg`` message descriptor must be
+constructed and sent via ``rte_mp_reply()`` function, along with ``peer``
+pointer. The resulting response will then be delivered to the correct requestor.
+
+Misc considerations
+~~~~~~~~~~~~~~~~~~~~~~~~
+
+Due to the underlying IPC implementation being single-threaded, recursive
+requests (i.e. sending a request while responding to another request) is not
+supported. However, since sending messages (not requests) does not involve an
+IPC thread, sending messages while processing another message or request is
+supported.
+
+Asynchronous request callbacks may be triggered either from IPC thread or from
+interrupt thread, depending on whether the request has timed out. It is
+therefore suggested to avoid waiting for interrupt-based events (such as alarms)
+inside asynchronous IPC request callbacks. This limitation does not apply to
+messages or synchronous requests.
+
+If callbacks spend a long time processing the incoming requests, the requestor
+might time out, so setting the right timeout value on the requestor side is
+imperative.
+
+If some of the messages timed out, ``nb_sent`` and ``nb_received`` fields in the
+``rte_mp_reply`` descriptor will not have matching values. This is not treated
+as error by the IPC API, and it is expected that the user will be responsible
+for deciding how to handle such cases.
+
+If a callback has been registered, IPC will assume that it is safe to call it.
+This is important when registering callbacks during DPDK initialization.
+During initialization, IPC will consider the receiving side as non-existing if
+the callback has not been registered yet. However, once the callback has been
+registered, it is expected that IPC should be safe to trigger it, even if the
+rest of the DPDK initialization hasn't finished yet.
git.droids-corp.org / dpdk.git / blobdiff