Then, the main() function is called. The core initialization and launch is done in rte_eal_init() (see the API documentation).
It consist of calls to the pthread library (more specifically, pthread_self(), pthread_create(), and pthread_setaffinity_np()).
-.. _figure_linuxapp_launch:
+.. _figure_linux_launch:
.. figure:: img/linuxapp_launch.*
.. note::
Initialization of objects, such as memory zones, rings, memory pools, lpm tables and hash tables,
- should be done as part of the overall application initialization on the master lcore.
+ should be done as part of the overall application initialization on the main lcore.
The creation and initialization functions for these objects are not multi-thread safe.
However, once initialized, the objects themselves can safely be used in multiple threads simultaneously.
Multi-process Support
~~~~~~~~~~~~~~~~~~~~~
-The Linuxapp EAL allows a multi-process as well as a multi-threaded (pthread) deployment model.
+The Linux EAL allows a multi-process as well as a multi-threaded (pthread) deployment model.
See chapter
:ref:`Multi-process Support <Multi-process_Support>` for more details.
``--socket-limit`` command-line option, for a simple way to limit maximum amount
of memory that can be used by DPDK application.
+.. warning::
+ Memory subsystem uses DPDK IPC internally, so memory allocations/callbacks
+ and IPC must not be mixed: it is not safe to allocate/free memory inside
+ memory-related or IPC callbacks, and it is not safe to use IPC inside
+ memory-related callbacks. See chapter
+ :ref:`Multi-process Support <Multi-process_Support>` for more details about
+ DPDK IPC.
+
+ Legacy memory mode
This mode is enabled by specifying ``--legacy-mem`` command-line switch to the
Additional restrictions are present when running in 32-bit mode. In dynamic
memory mode, by default maximum of 2 gigabytes of VA space will be preallocated,
-and all of it will be on master lcore NUMA node unless ``--socket-mem`` flag is
+and all of it will be on main lcore NUMA node unless ``--socket-mem`` flag is
used.
In legacy mode, VA space will only be preallocated for segments that were
of virtual memory being preallocated at startup by editing the following config
variables:
-* ``CONFIG_RTE_MAX_MEMSEG_LISTS`` controls how many segment lists can DPDK have
-* ``CONFIG_RTE_MAX_MEM_MB_PER_LIST`` controls how much megabytes of memory each
+* ``RTE_MAX_MEMSEG_LISTS`` controls how many segment lists can DPDK have
+* ``RTE_MAX_MEM_MB_PER_LIST`` controls how much megabytes of memory each
segment list can address
-* ``CONFIG_RTE_MAX_MEMSEG_PER_LIST`` controls how many segments each segment can
+* ``RTE_MAX_MEMSEG_PER_LIST`` controls how many segments each segment can
have
-* ``CONFIG_RTE_MAX_MEMSEG_PER_TYPE`` controls how many segments each memory type
+* ``RTE_MAX_MEMSEG_PER_TYPE`` controls how many segments each memory type
can have (where "type" is defined as "page size + NUMA node" combination)
-* ``CONFIG_RTE_MAX_MEM_MB_PER_TYPE`` controls how much megabytes of memory each
+* ``RTE_MAX_MEM_MB_PER_TYPE`` controls how much megabytes of memory each
memory type can address
-* ``CONFIG_RTE_MAX_MEM_MB`` places a global maximum on the amount of memory
+* ``RTE_MAX_MEM_MB`` places a global maximum on the amount of memory
DPDK can reserve
Normally, these options do not need to be changed.
can later be mapped into that preallocated VA space (if dynamic memory mode
is enabled), and can optionally be mapped into it at startup.
++ Segment file descriptors
+
+On Linux, in most cases, EAL will store segment file descriptors in EAL. This
+can become a problem when using smaller page sizes due to underlying limitations
+of ``glibc`` library. For example, Linux API calls such as ``select()`` may not
+work correctly because ``glibc`` does not support more than certain number of
+file descriptors.
+
+There are two possible solutions for this problem. The recommended solution is
+to use ``--single-file-segments`` mode, as that mode will not use a file
+descriptor per each page, and it will keep compatibility with Virtio with
+vhost-user backend. This option is not available when using ``--legacy-mem``
+mode.
+
+Another option is to use bigger page sizes. Since fewer pages are required to
+cover the same memory area, fewer file descriptors will be stored internally
+by EAL.
+
Support for Externally Allocated Memory
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+ Using heap API's for externally allocated memory
-Using using a set of malloc heap API's is the recommended way to use externally
+Using a set of malloc heap API's is the recommended way to use externally
allocated memory in DPDK. In this way, support for externally allocated memory
is implemented through overloading the socket ID - externally allocated heaps
will have socket ID's that would be considered invalid under normal
These API's are (as their name implies) intended to allow registering or
unregistering externally allocated memory to/from DPDK's internal page table, to
-allow API's like ``rte_virt2memseg`` etc. to work with externally allocated
+allow API's like ``rte_mem_virt2memseg`` etc. to work with externally allocated
memory. Memory added this way will not be available for any regular DPDK
allocators; DPDK will leave this memory for the user application to manage.
- If IOVA table is not specified, IOVA addresses will be assumed to be
unavailable
- Other processes must attach to the memory area before they can use it
-* Perform DMA mapping with ``rte_vfio_dma_map`` if needed
+* Perform DMA mapping with ``rte_dev_dma_map`` if needed
* Use the memory area in your application
* If memory area is no longer needed, it can be unregistered
- If the area was mapped for DMA, unmapping must be performed before
The RX interrupt is the first choice to be such kind of wake-up event, but probably won't be the only one.
EAL provides the event APIs for this event-driven thread mode.
-Taking linuxapp as an example, the implementation relies on epoll. Each thread can monitor an epoll instance
+Taking Linux as an example, the implementation relies on epoll. Each thread can monitor an epoll instance
in which all the wake-up events' file descriptors are added. The event file descriptors are created and mapped to
the interrupt vectors according to the UIO/VFIO spec.
From FreeBSD's perspective, kqueue is the alternative way, but not implemented yet.
callback. Care must be taken not to close the device from the interrupt handler
context. It is necessary to reschedule such closing operation.
-Blacklisting
-~~~~~~~~~~~~
+Block list
+~~~~~~~~~~
-The EAL PCI device blacklist functionality can be used to mark certain NIC ports as blacklisted,
+The EAL PCI device block list functionality can be used to mark certain NIC ports as unavailable,
so they are ignored by the DPDK.
-The ports to be blacklisted are identified using the PCIe* description (Domain:Bus:Device.Function).
+The ports to be blocked are identified using the PCIe* description (Domain:Bus:Device.Function).
Misc Functions
~~~~~~~~~~~~~~
Locks and atomic operations are per-architecture (i686 and x86_64).
+IOVA Mode Detection
+~~~~~~~~~~~~~~~~~~~
+
+IOVA Mode is selected by considering what the current usable Devices on the
+system require and/or support.
+
+On FreeBSD, RTE_IOVA_PA is always the default. On Linux, the IOVA mode is
+detected based on a 2-step heuristic detailed below.
+
+For the first step, EAL asks each bus its requirement in terms of IOVA mode
+and decides on a preferred IOVA mode.
+
+- if all buses report RTE_IOVA_PA, then the preferred IOVA mode is RTE_IOVA_PA,
+- if all buses report RTE_IOVA_VA, then the preferred IOVA mode is RTE_IOVA_VA,
+- if all buses report RTE_IOVA_DC, no bus expressed a preferrence, then the
+ preferred mode is RTE_IOVA_DC,
+- if the buses disagree (at least one wants RTE_IOVA_PA and at least one wants
+ RTE_IOVA_VA), then the preferred IOVA mode is RTE_IOVA_DC (see below with the
+ check on Physical Addresses availability),
+
+If the buses have expressed no preference on which IOVA mode to pick, then a
+default is selected using the following logic:
+
+- if physical addresses are not available, RTE_IOVA_VA mode is used
+- if /sys/kernel/iommu_groups is not empty, RTE_IOVA_VA mode is used
+- otherwise, RTE_IOVA_PA mode is used
+
+In the case when the buses had disagreed on their preferred IOVA mode, part of
+the buses won't work because of this decision.
+
+The second step checks if the preferred mode complies with the Physical
+Addresses availability since those are only available to root user in recent
+kernels. Namely, if the preferred mode is RTE_IOVA_PA but there is no access to
+Physical Addresses, then EAL init fails early, since later probing of the
+devices would fail anyway.
+
+.. note::
+
+ The RTE_IOVA_VA mode is preferred as the default in most cases for the
+ following reasons:
+
+ - All drivers are expected to work in RTE_IOVA_VA mode, irrespective of
+ physical address availability.
+ - By default, the mempool, first asks for IOVA-contiguous memory using
+ ``RTE_MEMZONE_IOVA_CONTIG``. This is slow in RTE_IOVA_PA mode and it may
+ affect the application boot time.
+ - It is easy to enable large amount of IOVA-contiguous memory use cases
+ with IOVA in VA mode.
+
+ It is expected that all PCI drivers work in both RTE_IOVA_PA and
+ RTE_IOVA_VA modes.
+
+ If a PCI driver does not support RTE_IOVA_PA mode, the
+ ``RTE_PCI_DRV_NEED_IOVA_AS_VA`` flag is used to dictate that this PCI
+ driver can only work in RTE_IOVA_VA mode.
+
+ When the KNI kernel module is detected, RTE_IOVA_PA mode is preferred as a
+ performance penalty is expected in RTE_IOVA_VA mode.
+
IOVA Mode Configuration
~~~~~~~~~~~~~~~~~~~~~~~
To facilitate forcing the IOVA mode to a specific value the EAL command line option ``--iova-mode`` can
be used to select either physical addressing('pa') or virtual addressing('va').
+.. _max_simd_bitwidth:
+
+
+Max SIMD bitwidth
+~~~~~~~~~~~~~~~~~
+
+The EAL provides a single setting to limit the max SIMD bitwidth used by DPDK,
+which is used in determining the vector path, if any, chosen by a component.
+The value can be set at runtime by an application using the
+'rte_vect_set_max_simd_bitwidth(uint16_t bitwidth)' function,
+which should only be called once at initialization, before EAL init.
+The value can be overridden by the user using the EAL command-line option '--force-max-simd-bitwidth'.
+
+When choosing a vector path, along with checking the CPU feature support,
+the value of the max SIMD bitwidth must also be checked, and can be retrieved using the
+'rte_vect_get_max_simd_bitwidth()' function.
+The value should be compared against the enum values for accepted max SIMD bitwidths:
+
+.. code-block:: c
+
+ enum rte_vect_max_simd {
+ RTE_VECT_SIMD_DISABLED = 64,
+ RTE_VECT_SIMD_128 = 128,
+ RTE_VECT_SIMD_256 = 256,
+ RTE_VECT_SIMD_512 = 512,
+ RTE_VECT_SIMD_MAX = INT16_MAX + 1,
+ };
+
+ if (rte_vect_get_max_simd_bitwidth() >= RTE_VECT_SIMD_512)
+ /* Take AVX-512 vector path */
+ else if (rte_vect_get_max_simd_bitwidth() >= RTE_VECT_SIMD_256)
+ /* Take AVX2 vector path */
+
+
Memory Segments and Memory Zones (memzone)
------------------------------------------
non-EAL pthread support
~~~~~~~~~~~~~~~~~~~~~~~
-It is possible to use the DPDK execution context with any user pthread (aka. Non-EAL pthreads).
-In a non-EAL pthread, the *_lcore_id* is always LCORE_ID_ANY which identifies that it is not an EAL thread with a valid, unique, *_lcore_id*.
-Some libraries will use an alternative unique ID (e.g. TID), some will not be impacted at all, and some will work but with limitations (e.g. timer and mempool libraries).
+It is possible to use the DPDK execution context with any user pthread (aka. non-EAL pthreads).
+There are two kinds of non-EAL pthreads:
+
+- a registered non-EAL pthread with a valid *_lcore_id* that was successfully assigned by calling ``rte_thread_register()``,
+- a non registered non-EAL pthread with a LCORE_ID_ANY,
+
+For non registered non-EAL pthread (with a LCORE_ID_ANY *_lcore_id*), some libraries will use an alternative unique ID (e.g. TID), some will not be impacted at all, and some will work but with limitations (e.g. timer and mempool libraries).
All these impacts are mentioned in :ref:`known_issue_label` section.
- with affinity restricted to 2-4, the Control Threads will end up on
CPU 4.
- with affinity restricted to 2-3, the Control Threads will end up on
- CPU 2 (master lcore, which is the default when no CPU is available).
+ CPU 2 (main lcore, which is the default when no CPU is available).
.. _known_issue_label:
+ rte_mempool
The rte_mempool uses a per-lcore cache inside the mempool.
- For non-EAL pthreads, ``rte_lcore_id()`` will not return a valid number.
- So for now, when rte_mempool is used with non-EAL pthreads, the put/get operations will bypass the default mempool cache and there is a performance penalty because of this bypass.
- Only user-owned external caches can be used in a non-EAL context in conjunction with ``rte_mempool_generic_put()`` and ``rte_mempool_generic_get()`` that accept an explicit cache parameter.
+ For unregistered non-EAL pthreads, ``rte_lcore_id()`` will not return a valid number.
+ So for now, when rte_mempool is used with unregistered non-EAL pthreads, the put/get operations will bypass the default mempool cache and there is a performance penalty because of this bypass.
+ Only user-owned external caches can be used in an unregistered non-EAL context in conjunction with ``rte_mempool_generic_put()`` and ``rte_mempool_generic_get()`` that accept an explicit cache parameter.
+ rte_ring
5. It MUST not be used by multi-producer/consumer pthreads, whose scheduling policies are SCHED_FIFO or SCHED_RR.
+ Alternatively, applications can use the lock-free stack mempool handler. When
+ considering this handler, note that:
+
+ - It is currently limited to the aarch64 and x86_64 platforms, because it uses
+ an instruction (16-byte compare-and-swap) that is not yet available on other
+ platforms.
+ - It has worse average-case performance than the non-preemptive rte_ring, but
+ software caching (e.g. the mempool cache) can mitigate this by reducing the
+ number of stack accesses.
+
+ rte_timer
- Running ``rte_timer_manage()`` on a non-EAL pthread is not allowed. However, resetting/stopping the timer from a non-EAL pthread is allowed.
+ Running ``rte_timer_manage()`` on an unregistered non-EAL pthread is not allowed. However, resetting/stopping the timer from a non-EAL pthread is allowed.
+ rte_log
- In non-EAL pthreads, there is no per thread loglevel and logtype, global loglevels are used.
+ In unregistered non-EAL pthreads, there is no per thread loglevel and logtype, global loglevels are used.
+ misc
- The debug statistics of rte_ring, rte_mempool and rte_timer are not supported in a non-EAL pthread.
+ The debug statistics of rte_ring, rte_mempool and rte_timer are not supported in an unregistered non-EAL pthread.
cgroup control
~~~~~~~~~~~~~~
Refer to the rte_malloc() function description in the *DPDK API Reference*
manual for more information.
-Cookies
-~~~~~~~
-
-When CONFIG_RTE_MALLOC_DEBUG is enabled, the allocated memory contains
-overwrite protection fields to help identify buffer overflows.
Alignment and NUMA Constraints
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Malloc heap is a doubly-linked list, where each element keeps track of its
previous and next elements. Due to the fact that hugepage memory can come and
-go, neighbouring malloc elements may not necessarily be adjacent in memory.
+go, neighboring malloc elements may not necessarily be adjacent in memory.
Also, since a malloc element may span multiple pages, its contents may not
necessarily be IOVA-contiguous either - each malloc element is only guaranteed
to be virtually contiguous.
git.droids-corp.org / dpdk.git / blobdiff