1.. SPDX-License-Identifier: BSD-3-Clause 2 Copyright(c) 2010-2014 Intel Corporation. 3 4.. _Environment_Abstraction_Layer: 5 6Environment Abstraction Layer 7============================= 8 9The Environment Abstraction Layer (EAL) is responsible for gaining access to low-level resources such as hardware and memory space. 10It provides a generic interface that hides the environment specifics from the applications and libraries. 11It is the responsibility of the initialization routine to decide how to allocate these resources 12(that is, memory space, devices, timers, consoles, and so on). 13 14Typical services expected from the EAL are: 15 16* DPDK Loading and Launching: 17 The DPDK and its application are linked as a single application and must be loaded by some means. 18 19* Core Affinity/Assignment Procedures: 20 The EAL provides mechanisms for assigning execution units to specific cores as well as creating execution instances. 21 22* System Memory Reservation: 23 The EAL facilitates the reservation of different memory zones, for example, physical memory areas for device interactions. 24 25* Trace and Debug Functions: Logs, dump_stack, panic and so on. 26 27* Utility Functions: Spinlocks and atomic counters that are not provided in libc. 28 29* CPU Feature Identification: Determine at runtime if a particular feature, for example, Intel® AVX is supported. 30 Determine if the current CPU supports the feature set that the binary was compiled for. 31 32* Interrupt Handling: Interfaces to register/unregister callbacks to specific interrupt sources. 33 34* Alarm Functions: Interfaces to set/remove callbacks to be run at a specific time. 35 36EAL in a Linux-userland Execution Environment 37--------------------------------------------- 38 39In a Linux user space environment, the DPDK application runs as a user-space application using the pthread library. 40 41The EAL performs physical memory allocation using mmap() in hugetlbfs (using huge page sizes to increase performance). 42This memory is exposed to DPDK service layers such as the :ref:`Mempool Library <Mempool_Library>`. 43 44At this point, the DPDK services layer will be initialized, then through pthread setaffinity calls, 45each execution unit will be assigned to a specific logical core to run as a user-level thread. 46 47The time reference is provided by the CPU Time-Stamp Counter (TSC) or by the HPET kernel API through a mmap() call. 48 49Initialization and Core Launching 50~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ 51 52Part of the initialization is done by the start function of glibc. 53A check is also performed at initialization time to ensure that the micro architecture type chosen in the config file is supported by the CPU. 54Then, the main() function is called. The core initialization and launch is done in rte_eal_init() (see the API documentation). 55It consist of calls to the pthread library (more specifically, pthread_self(), pthread_create(), and pthread_setaffinity_np()). 56 57.. _figure_linux_launch: 58 59.. figure:: img/linuxapp_launch.* 60 61 EAL Initialization in a Linux Application Environment 62 63 64.. note:: 65 66 Initialization of objects, such as memory zones, rings, memory pools, lpm tables and hash tables, 67 should be done as part of the overall application initialization on the master lcore. 68 The creation and initialization functions for these objects are not multi-thread safe. 69 However, once initialized, the objects themselves can safely be used in multiple threads simultaneously. 70 71Shutdown and Cleanup 72~~~~~~~~~~~~~~~~~~~~ 73 74During the initialization of EAL resources such as hugepage backed memory can be 75allocated by core components. The memory allocated during ``rte_eal_init()`` 76can be released by calling the ``rte_eal_cleanup()`` function. Refer to the 77API documentation for details. 78 79Multi-process Support 80~~~~~~~~~~~~~~~~~~~~~ 81 82The Linux EAL allows a multi-process as well as a multi-threaded (pthread) deployment model. 83See chapter 84:ref:`Multi-process Support <Multi-process_Support>` for more details. 85 86Memory Mapping Discovery and Memory Reservation 87~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ 88 89The allocation of large contiguous physical memory is done using the hugetlbfs kernel filesystem. 90The EAL provides an API to reserve named memory zones in this contiguous memory. 91The physical address of the reserved memory for that memory zone is also returned to the user by the memory zone reservation API. 92 93There are two modes in which DPDK memory subsystem can operate: dynamic mode, 94and legacy mode. Both modes are explained below. 95 96.. note:: 97 98 Memory reservations done using the APIs provided by rte_malloc are also backed by pages from the hugetlbfs filesystem. 99 100+ Dynamic memory mode 101 102Currently, this mode is only supported on Linux. 103 104In this mode, usage of hugepages by DPDK application will grow and shrink based 105on application's requests. Any memory allocation through ``rte_malloc()``, 106``rte_memzone_reserve()`` or other methods, can potentially result in more 107hugepages being reserved from the system. Similarly, any memory deallocation can 108potentially result in hugepages being released back to the system. 109 110Memory allocated in this mode is not guaranteed to be IOVA-contiguous. If large 111chunks of IOVA-contiguous are required (with "large" defined as "more than one 112page"), it is recommended to either use VFIO driver for all physical devices (so 113that IOVA and VA addresses can be the same, thereby bypassing physical addresses 114entirely), or use legacy memory mode. 115 116For chunks of memory which must be IOVA-contiguous, it is recommended to use 117``rte_memzone_reserve()`` function with ``RTE_MEMZONE_IOVA_CONTIG`` flag 118specified. This way, memory allocator will ensure that, whatever memory mode is 119in use, either reserved memory will satisfy the requirements, or the allocation 120will fail. 121 122There is no need to preallocate any memory at startup using ``-m`` or 123``--socket-mem`` command-line parameters, however it is still possible to do so, 124in which case preallocate memory will be "pinned" (i.e. will never be released 125by the application back to the system). It will be possible to allocate more 126hugepages, and deallocate those, but any preallocated pages will not be freed. 127If neither ``-m`` nor ``--socket-mem`` were specified, no memory will be 128preallocated, and all memory will be allocated at runtime, as needed. 129 130Another available option to use in dynamic memory mode is 131``--single-file-segments`` command-line option. This option will put pages in 132single files (per memseg list), as opposed to creating a file per page. This is 133normally not needed, but can be useful for use cases like userspace vhost, where 134there is limited number of page file descriptors that can be passed to VirtIO. 135 136If the application (or DPDK-internal code, such as device drivers) wishes to 137receive notifications about newly allocated memory, it is possible to register 138for memory event callbacks via ``rte_mem_event_callback_register()`` function. 139This will call a callback function any time DPDK's memory map has changed. 140 141If the application (or DPDK-internal code, such as device drivers) wishes to be 142notified about memory allocations above specified threshold (and have a chance 143to deny them), allocation validator callbacks are also available via 144``rte_mem_alloc_validator_callback_register()`` function. 145 146A default validator callback is provided by EAL, which can be enabled with a 147``--socket-limit`` command-line option, for a simple way to limit maximum amount 148of memory that can be used by DPDK application. 149 150+ Legacy memory mode 151 152This mode is enabled by specifying ``--legacy-mem`` command-line switch to the 153EAL. This switch will have no effect on FreeBSD as FreeBSD only supports 154legacy mode anyway. 155 156This mode mimics historical behavior of EAL. That is, EAL will reserve all 157memory at startup, sort all memory into large IOVA-contiguous chunks, and will 158not allow acquiring or releasing hugepages from the system at runtime. 159 160If neither ``-m`` nor ``--socket-mem`` were specified, the entire available 161hugepage memory will be preallocated. 162 163+ Hugepage allocation matching 164 165This behavior is enabled by specifying the ``--match-allocations`` command-line 166switch to the EAL. This switch is Linux-only and not supported with 167``--legacy-mem`` nor ``--no-huge``. 168 169Some applications using memory event callbacks may require that hugepages be 170freed exactly as they were allocated. These applications may also require 171that any allocation from the malloc heap not span across allocations 172associated with two different memory event callbacks. Hugepage allocation 173matching can be used by these types of applications to satisfy both of these 174requirements. This can result in some increased memory usage which is 175very dependent on the memory allocation patterns of the application. 176 177+ 32-bit support 178 179Additional restrictions are present when running in 32-bit mode. In dynamic 180memory mode, by default maximum of 2 gigabytes of VA space will be preallocated, 181and all of it will be on master lcore NUMA node unless ``--socket-mem`` flag is 182used. 183 184In legacy mode, VA space will only be preallocated for segments that were 185requested (plus padding, to keep IOVA-contiguousness). 186 187+ Maximum amount of memory 188 189All possible virtual memory space that can ever be used for hugepage mapping in 190a DPDK process is preallocated at startup, thereby placing an upper limit on how 191much memory a DPDK application can have. DPDK memory is stored in segment lists, 192each segment is strictly one physical page. It is possible to change the amount 193of virtual memory being preallocated at startup by editing the following config 194variables: 195 196* ``CONFIG_RTE_MAX_MEMSEG_LISTS`` controls how many segment lists can DPDK have 197* ``CONFIG_RTE_MAX_MEM_MB_PER_LIST`` controls how much megabytes of memory each 198 segment list can address 199* ``CONFIG_RTE_MAX_MEMSEG_PER_LIST`` controls how many segments each segment can 200 have 201* ``CONFIG_RTE_MAX_MEMSEG_PER_TYPE`` controls how many segments each memory type 202 can have (where "type" is defined as "page size + NUMA node" combination) 203* ``CONFIG_RTE_MAX_MEM_MB_PER_TYPE`` controls how much megabytes of memory each 204 memory type can address 205* ``CONFIG_RTE_MAX_MEM_MB`` places a global maximum on the amount of memory 206 DPDK can reserve 207 208Normally, these options do not need to be changed. 209 210.. note:: 211 212 Preallocated virtual memory is not to be confused with preallocated hugepage 213 memory! All DPDK processes preallocate virtual memory at startup. Hugepages 214 can later be mapped into that preallocated VA space (if dynamic memory mode 215 is enabled), and can optionally be mapped into it at startup. 216 217+ Segment file descriptors 218 219On Linux, in most cases, EAL will store segment file descriptors in EAL. This 220can become a problem when using smaller page sizes due to underlying limitations 221of ``glibc`` library. For example, Linux API calls such as ``select()`` may not 222work correctly because ``glibc`` does not support more than certain number of 223file descriptors. 224 225There are two possible solutions for this problem. The recommended solution is 226to use ``--single-file-segments`` mode, as that mode will not use a file 227descriptor per each page, and it will keep compatibility with Virtio with 228vhost-user backend. This option is not available when using ``--legacy-mem`` 229mode. 230 231Another option is to use bigger page sizes. Since fewer pages are required to 232cover the same memory area, fewer file descriptors will be stored internally 233by EAL. 234 235Support for Externally Allocated Memory 236~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ 237 238It is possible to use externally allocated memory in DPDK. There are two ways in 239which using externally allocated memory can work: the malloc heap API's, and 240manual memory management. 241 242+ Using heap API's for externally allocated memory 243 244Using using a set of malloc heap API's is the recommended way to use externally 245allocated memory in DPDK. In this way, support for externally allocated memory 246is implemented through overloading the socket ID - externally allocated heaps 247will have socket ID's that would be considered invalid under normal 248circumstances. Requesting an allocation to take place from a specified 249externally allocated memory is a matter of supplying the correct socket ID to 250DPDK allocator, either directly (e.g. through a call to ``rte_malloc``) or 251indirectly (through data structure-specific allocation API's such as 252``rte_ring_create``). Using these API's also ensures that mapping of externally 253allocated memory for DMA is also performed on any memory segment that is added 254to a DPDK malloc heap. 255 256Since there is no way DPDK can verify whether memory is available or valid, this 257responsibility falls on the shoulders of the user. All multiprocess 258synchronization is also user's responsibility, as well as ensuring that all 259calls to add/attach/detach/remove memory are done in the correct order. It is 260not required to attach to a memory area in all processes - only attach to memory 261areas as needed. 262 263The expected workflow is as follows: 264 265* Get a pointer to memory area 266* Create a named heap 267* Add memory area(s) to the heap 268 - If IOVA table is not specified, IOVA addresses will be assumed to be 269 unavailable, and DMA mappings will not be performed 270 - Other processes must attach to the memory area before they can use it 271* Get socket ID used for the heap 272* Use normal DPDK allocation procedures, using supplied socket ID 273* If memory area is no longer needed, it can be removed from the heap 274 - Other processes must detach from this memory area before it can be removed 275* If heap is no longer needed, remove it 276 - Socket ID will become invalid and will not be reused 277 278For more information, please refer to ``rte_malloc`` API documentation, 279specifically the ``rte_malloc_heap_*`` family of function calls. 280 281+ Using externally allocated memory without DPDK API's 282 283While using heap API's is the recommended method of using externally allocated 284memory in DPDK, there are certain use cases where the overhead of DPDK heap API 285is undesirable - for example, when manual memory management is performed on an 286externally allocated area. To support use cases where externally allocated 287memory will not be used as part of normal DPDK workflow, there is also another 288set of API's under the ``rte_extmem_*`` namespace. 289 290These API's are (as their name implies) intended to allow registering or 291unregistering externally allocated memory to/from DPDK's internal page table, to 292allow API's like ``rte_virt2memseg`` etc. to work with externally allocated 293memory. Memory added this way will not be available for any regular DPDK 294allocators; DPDK will leave this memory for the user application to manage. 295 296The expected workflow is as follows: 297 298* Get a pointer to memory area 299* Register memory within DPDK 300 - If IOVA table is not specified, IOVA addresses will be assumed to be 301 unavailable 302 - Other processes must attach to the memory area before they can use it 303* Perform DMA mapping with ``rte_dev_dma_map`` if needed 304* Use the memory area in your application 305* If memory area is no longer needed, it can be unregistered 306 - If the area was mapped for DMA, unmapping must be performed before 307 unregistering memory 308 - Other processes must detach from the memory area before it can be 309 unregistered 310 311Since these externally allocated memory areas will not be managed by DPDK, it is 312therefore up to the user application to decide how to use them and what to do 313with them once they're registered. 314 315Per-lcore and Shared Variables 316~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ 317 318.. note:: 319 320 lcore refers to a logical execution unit of the processor, sometimes called a hardware *thread*. 321 322Shared variables are the default behavior. 323Per-lcore variables are implemented using *Thread Local Storage* (TLS) to provide per-thread local storage. 324 325Logs 326~~~~ 327 328A logging API is provided by EAL. 329By default, in a Linux application, logs are sent to syslog and also to the console. 330However, the log function can be overridden by the user to use a different logging mechanism. 331 332Trace and Debug Functions 333^^^^^^^^^^^^^^^^^^^^^^^^^ 334 335There are some debug functions to dump the stack in glibc. 336The rte_panic() function can voluntarily provoke a SIG_ABORT, 337which can trigger the generation of a core file, readable by gdb. 338 339CPU Feature Identification 340~~~~~~~~~~~~~~~~~~~~~~~~~~ 341 342The EAL can query the CPU at runtime (using the rte_cpu_get_features() function) to determine which CPU features are available. 343 344User Space Interrupt Event 345~~~~~~~~~~~~~~~~~~~~~~~~~~ 346 347+ User Space Interrupt and Alarm Handling in Host Thread 348 349The EAL creates a host thread to poll the UIO device file descriptors to detect the interrupts. 350Callbacks can be registered or unregistered by the EAL functions for a specific interrupt event 351and are called in the host thread asynchronously. 352The EAL also allows timed callbacks to be used in the same way as for NIC interrupts. 353 354.. note:: 355 356 In DPDK PMD, the only interrupts handled by the dedicated host thread are those for link status change 357 (link up and link down notification) and for sudden device removal. 358 359 360+ RX Interrupt Event 361 362The receive and transmit routines provided by each PMD don't limit themselves to execute in polling thread mode. 363To ease the idle polling with tiny throughput, it's useful to pause the polling and wait until the wake-up event happens. 364The RX interrupt is the first choice to be such kind of wake-up event, but probably won't be the only one. 365 366EAL provides the event APIs for this event-driven thread mode. 367Taking Linux as an example, the implementation relies on epoll. Each thread can monitor an epoll instance 368in which all the wake-up events' file descriptors are added. The event file descriptors are created and mapped to 369the interrupt vectors according to the UIO/VFIO spec. 370From FreeBSD's perspective, kqueue is the alternative way, but not implemented yet. 371 372EAL initializes the mapping between event file descriptors and interrupt vectors, while each device initializes the mapping 373between interrupt vectors and queues. In this way, EAL actually is unaware of the interrupt cause on the specific vector. 374The eth_dev driver takes responsibility to program the latter mapping. 375 376.. note:: 377 378 Per queue RX interrupt event is only allowed in VFIO which supports multiple MSI-X vector. In UIO, the RX interrupt 379 together with other interrupt causes shares the same vector. In this case, when RX interrupt and LSC(link status change) 380 interrupt are both enabled(intr_conf.lsc == 1 && intr_conf.rxq == 1), only the former is capable. 381 382The RX interrupt are controlled/enabled/disabled by ethdev APIs - 'rte_eth_dev_rx_intr_*'. They return failure if the PMD 383hasn't support them yet. The intr_conf.rxq flag is used to turn on the capability of RX interrupt per device. 384 385+ Device Removal Event 386 387This event is triggered by a device being removed at a bus level. Its 388underlying resources may have been made unavailable (i.e. PCI mappings 389unmapped). The PMD must make sure that on such occurrence, the application can 390still safely use its callbacks. 391 392This event can be subscribed to in the same way one would subscribe to a link 393status change event. The execution context is thus the same, i.e. it is the 394dedicated interrupt host thread. 395 396Considering this, it is likely that an application would want to close a 397device having emitted a Device Removal Event. In such case, calling 398``rte_eth_dev_close()`` can trigger it to unregister its own Device Removal Event 399callback. Care must be taken not to close the device from the interrupt handler 400context. It is necessary to reschedule such closing operation. 401 402Blacklisting 403~~~~~~~~~~~~ 404 405The EAL PCI device blacklist functionality can be used to mark certain NIC ports as blacklisted, 406so they are ignored by the DPDK. 407The ports to be blacklisted are identified using the PCIe* description (Domain:Bus:Device.Function). 408 409Misc Functions 410~~~~~~~~~~~~~~ 411 412Locks and atomic operations are per-architecture (i686 and x86_64). 413 414IOVA Mode Configuration 415~~~~~~~~~~~~~~~~~~~~~~~ 416 417Auto detection of the IOVA mode, based on probing the bus and IOMMU configuration, may not report 418the desired addressing mode when virtual devices that are not directly attached to the bus are present. 419To facilitate forcing the IOVA mode to a specific value the EAL command line option ``--iova-mode`` can 420be used to select either physical addressing('pa') or virtual addressing('va'). 421 422Memory Segments and Memory Zones (memzone) 423------------------------------------------ 424 425The mapping of physical memory is provided by this feature in the EAL. 426As physical memory can have gaps, the memory is described in a table of descriptors, 427and each descriptor (called rte_memseg ) describes a physical page. 428 429On top of this, the memzone allocator's role is to reserve contiguous portions of physical memory. 430These zones are identified by a unique name when the memory is reserved. 431 432The rte_memzone descriptors are also located in the configuration structure. 433This structure is accessed using rte_eal_get_configuration(). 434The lookup (by name) of a memory zone returns a descriptor containing the physical address of the memory zone. 435 436Memory zones can be reserved with specific start address alignment by supplying the align parameter 437(by default, they are aligned to cache line size). 438The alignment value should be a power of two and not less than the cache line size (64 bytes). 439Memory zones can also be reserved from either 2 MB or 1 GB hugepages, provided that both are available on the system. 440 441Both memsegs and memzones are stored using ``rte_fbarray`` structures. Please 442refer to *DPDK API Reference* for more information. 443 444 445Multiple pthread 446---------------- 447 448DPDK usually pins one pthread per core to avoid the overhead of task switching. 449This allows for significant performance gains, but lacks flexibility and is not always efficient. 450 451Power management helps to improve the CPU efficiency by limiting the CPU runtime frequency. 452However, alternately it is possible to utilize the idle cycles available to take advantage of 453the full capability of the CPU. 454 455By taking advantage of cgroup, the CPU utilization quota can be simply assigned. 456This gives another way to improve the CPU efficiency, however, there is a prerequisite; 457DPDK must handle the context switching between multiple pthreads per core. 458 459For further flexibility, it is useful to set pthread affinity not only to a CPU but to a CPU set. 460 461EAL pthread and lcore Affinity 462~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ 463 464The term "lcore" refers to an EAL thread, which is really a Linux/FreeBSD pthread. 465"EAL pthreads" are created and managed by EAL and execute the tasks issued by *remote_launch*. 466In each EAL pthread, there is a TLS (Thread Local Storage) called *_lcore_id* for unique identification. 467As EAL pthreads usually bind 1:1 to the physical CPU, the *_lcore_id* is typically equal to the CPU ID. 468 469When using multiple pthreads, however, the binding is no longer always 1:1 between an EAL pthread and a specified physical CPU. 470The EAL pthread may have affinity to a CPU set, and as such the *_lcore_id* will not be the same as the CPU ID. 471For this reason, there is an EAL long option '--lcores' defined to assign the CPU affinity of lcores. 472For a specified lcore ID or ID group, the option allows setting the CPU set for that EAL pthread. 473 474The format pattern: 475 --lcores='<lcore_set>[@cpu_set][,<lcore_set>[@cpu_set],...]' 476 477'lcore_set' and 'cpu_set' can be a single number, range or a group. 478 479A number is a "digit([0-9]+)"; a range is "<number>-<number>"; a group is "(<number|range>[,<number|range>,...])". 480 481If a '\@cpu_set' value is not supplied, the value of 'cpu_set' will default to the value of 'lcore_set'. 482 483 :: 484 485 For example, "--lcores='1,2@(5-7),(3-5)@(0,2),(0,6),7-8'" which means start 9 EAL thread; 486 lcore 0 runs on cpuset 0x41 (cpu 0,6); 487 lcore 1 runs on cpuset 0x2 (cpu 1); 488 lcore 2 runs on cpuset 0xe0 (cpu 5,6,7); 489 lcore 3,4,5 runs on cpuset 0x5 (cpu 0,2); 490 lcore 6 runs on cpuset 0x41 (cpu 0,6); 491 lcore 7 runs on cpuset 0x80 (cpu 7); 492 lcore 8 runs on cpuset 0x100 (cpu 8). 493 494Using this option, for each given lcore ID, the associated CPUs can be assigned. 495It's also compatible with the pattern of corelist('-l') option. 496 497non-EAL pthread support 498~~~~~~~~~~~~~~~~~~~~~~~ 499 500It is possible to use the DPDK execution context with any user pthread (aka. Non-EAL pthreads). 501In 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*. 502Some 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). 503 504All these impacts are mentioned in :ref:`known_issue_label` section. 505 506Public Thread API 507~~~~~~~~~~~~~~~~~ 508 509There are two public APIs ``rte_thread_set_affinity()`` and ``rte_thread_get_affinity()`` introduced for threads. 510When they're used in any pthread context, the Thread Local Storage(TLS) will be set/get. 511 512Those TLS include *_cpuset* and *_socket_id*: 513 514* *_cpuset* stores the CPUs bitmap to which the pthread is affinitized. 515 516* *_socket_id* stores the NUMA node of the CPU set. If the CPUs in CPU set belong to different NUMA node, the *_socket_id* will be set to SOCKET_ID_ANY. 517 518 519Control Thread API 520~~~~~~~~~~~~~~~~~~ 521 522It is possible to create Control Threads using the public API 523``rte_ctrl_thread_create()``. 524Those threads can be used for management/infrastructure tasks and are used 525internally by DPDK for multi process support and interrupt handling. 526 527Those threads will be scheduled on CPUs part of the original process CPU 528affinity from which the dataplane and service lcores are excluded. 529 530For example, on a 8 CPUs system, starting a dpdk application with -l 2,3 531(dataplane cores), then depending on the affinity configuration which can be 532controlled with tools like taskset (Linux) or cpuset (FreeBSD), 533 534- with no affinity configuration, the Control Threads will end up on 535 0-1,4-7 CPUs. 536- with affinity restricted to 2-4, the Control Threads will end up on 537 CPU 4. 538- with affinity restricted to 2-3, the Control Threads will end up on 539 CPU 2 (master lcore, which is the default when no CPU is available). 540 541.. _known_issue_label: 542 543Known Issues 544~~~~~~~~~~~~ 545 546+ rte_mempool 547 548 The rte_mempool uses a per-lcore cache inside the mempool. 549 For non-EAL pthreads, ``rte_lcore_id()`` will not return a valid number. 550 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. 551 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. 552 553+ rte_ring 554 555 rte_ring supports multi-producer enqueue and multi-consumer dequeue. 556 However, it is non-preemptive, this has a knock on effect of making rte_mempool non-preemptable. 557 558 .. note:: 559 560 The "non-preemptive" constraint means: 561 562 - a pthread doing multi-producers enqueues on a given ring must not 563 be preempted by another pthread doing a multi-producer enqueue on 564 the same ring. 565 - a pthread doing multi-consumers dequeues on a given ring must not 566 be preempted by another pthread doing a multi-consumer dequeue on 567 the same ring. 568 569 Bypassing this constraint may cause the 2nd pthread to spin until the 1st one is scheduled again. 570 Moreover, if the 1st pthread is preempted by a context that has an higher priority, it may even cause a dead lock. 571 572 This means, use cases involving preemptible pthreads should consider using rte_ring carefully. 573 574 1. It CAN be used for preemptible single-producer and single-consumer use case. 575 576 2. It CAN be used for non-preemptible multi-producer and preemptible single-consumer use case. 577 578 3. It CAN be used for preemptible single-producer and non-preemptible multi-consumer use case. 579 580 4. It MAY be used by preemptible multi-producer and/or preemptible multi-consumer pthreads whose scheduling policy are all SCHED_OTHER(cfs), SCHED_IDLE or SCHED_BATCH. User SHOULD be aware of the performance penalty before using it. 581 582 5. It MUST not be used by multi-producer/consumer pthreads, whose scheduling policies are SCHED_FIFO or SCHED_RR. 583 584 Alternatively, applications can use the lock-free stack mempool handler. When 585 considering this handler, note that: 586 587 - It is currently limited to the x86_64 platform, because it uses an 588 instruction (16-byte compare-and-swap) that is not yet available on other 589 platforms. 590 - It has worse average-case performance than the non-preemptive rte_ring, but 591 software caching (e.g. the mempool cache) can mitigate this by reducing the 592 number of stack accesses. 593 594+ rte_timer 595 596 Running ``rte_timer_manage()`` on a non-EAL pthread is not allowed. However, resetting/stopping the timer from a non-EAL pthread is allowed. 597 598+ rte_log 599 600 In non-EAL pthreads, there is no per thread loglevel and logtype, global loglevels are used. 601 602+ misc 603 604 The debug statistics of rte_ring, rte_mempool and rte_timer are not supported in a non-EAL pthread. 605 606cgroup control 607~~~~~~~~~~~~~~ 608 609The following is a simple example of cgroup control usage, there are two pthreads(t0 and t1) doing packet I/O on the same core ($CPU). 610We expect only 50% of CPU spend on packet IO. 611 612 .. code-block:: console 613 614 mkdir /sys/fs/cgroup/cpu/pkt_io 615 mkdir /sys/fs/cgroup/cpuset/pkt_io 616 617 echo $cpu > /sys/fs/cgroup/cpuset/cpuset.cpus 618 619 echo $t0 > /sys/fs/cgroup/cpu/pkt_io/tasks 620 echo $t0 > /sys/fs/cgroup/cpuset/pkt_io/tasks 621 622 echo $t1 > /sys/fs/cgroup/cpu/pkt_io/tasks 623 echo $t1 > /sys/fs/cgroup/cpuset/pkt_io/tasks 624 625 cd /sys/fs/cgroup/cpu/pkt_io 626 echo 100000 > pkt_io/cpu.cfs_period_us 627 echo 50000 > pkt_io/cpu.cfs_quota_us 628 629 630Malloc 631------ 632 633The EAL provides a malloc API to allocate any-sized memory. 634 635The objective of this API is to provide malloc-like functions to allow 636allocation from hugepage memory and to facilitate application porting. 637The *DPDK API Reference* manual describes the available functions. 638 639Typically, these kinds of allocations should not be done in data plane 640processing because they are slower than pool-based allocation and make 641use of locks within the allocation and free paths. 642However, they can be used in configuration code. 643 644Refer to the rte_malloc() function description in the *DPDK API Reference* 645manual for more information. 646 647Cookies 648~~~~~~~ 649 650When CONFIG_RTE_MALLOC_DEBUG is enabled, the allocated memory contains 651overwrite protection fields to help identify buffer overflows. 652 653Alignment and NUMA Constraints 654~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ 655 656The rte_malloc() takes an align argument that can be used to request a memory 657area that is aligned on a multiple of this value (which must be a power of two). 658 659On systems with NUMA support, a call to the rte_malloc() function will return 660memory that has been allocated on the NUMA socket of the core which made the call. 661A set of APIs is also provided, to allow memory to be explicitly allocated on a 662NUMA socket directly, or by allocated on the NUMA socket where another core is 663located, in the case where the memory is to be used by a logical core other than 664on the one doing the memory allocation. 665 666Use Cases 667~~~~~~~~~ 668 669This API is meant to be used by an application that requires malloc-like 670functions at initialization time. 671 672For allocating/freeing data at runtime, in the fast-path of an application, 673the memory pool library should be used instead. 674 675Internal Implementation 676~~~~~~~~~~~~~~~~~~~~~~~ 677 678Data Structures 679^^^^^^^^^^^^^^^ 680 681There are two data structure types used internally in the malloc library: 682 683* struct malloc_heap - used to track free space on a per-socket basis 684 685* struct malloc_elem - the basic element of allocation and free-space 686 tracking inside the library. 687 688Structure: malloc_heap 689"""""""""""""""""""""" 690 691The malloc_heap structure is used to manage free space on a per-socket basis. 692Internally, there is one heap structure per NUMA node, which allows us to 693allocate memory to a thread based on the NUMA node on which this thread runs. 694While this does not guarantee that the memory will be used on that NUMA node, 695it is no worse than a scheme where the memory is always allocated on a fixed 696or random node. 697 698The key fields of the heap structure and their function are described below 699(see also diagram above): 700 701* lock - the lock field is needed to synchronize access to the heap. 702 Given that the free space in the heap is tracked using a linked list, 703 we need a lock to prevent two threads manipulating the list at the same time. 704 705* free_head - this points to the first element in the list of free nodes for 706 this malloc heap. 707 708* first - this points to the first element in the heap. 709 710* last - this points to the last element in the heap. 711 712.. _figure_malloc_heap: 713 714.. figure:: img/malloc_heap.* 715 716 Example of a malloc heap and malloc elements within the malloc library 717 718 719.. _malloc_elem: 720 721Structure: malloc_elem 722"""""""""""""""""""""" 723 724The malloc_elem structure is used as a generic header structure for various 725blocks of memory. 726It is used in two different ways - all shown in the diagram above: 727 728#. As a header on a block of free or allocated memory - normal case 729 730#. As a padding header inside a block of memory 731 732The most important fields in the structure and how they are used are described below. 733 734Malloc heap is a doubly-linked list, where each element keeps track of its 735previous and next elements. Due to the fact that hugepage memory can come and 736go, neighbouring malloc elements may not necessarily be adjacent in memory. 737Also, since a malloc element may span multiple pages, its contents may not 738necessarily be IOVA-contiguous either - each malloc element is only guaranteed 739to be virtually contiguous. 740 741.. note:: 742 743 If the usage of a particular field in one of the above three usages is not 744 described, the field can be assumed to have an undefined value in that 745 situation, for example, for padding headers only the "state" and "pad" 746 fields have valid values. 747 748* heap - this pointer is a reference back to the heap structure from which 749 this block was allocated. 750 It is used for normal memory blocks when they are being freed, to add the 751 newly-freed block to the heap's free-list. 752 753* prev - this pointer points to previous header element/block in memory. When 754 freeing a block, this pointer is used to reference the previous block to 755 check if that block is also free. If so, and the two blocks are immediately 756 adjacent to each other, then the two free blocks are merged to form a single 757 larger block. 758 759* next - this pointer points to next header element/block in memory. When 760 freeing a block, this pointer is used to reference the next block to check 761 if that block is also free. If so, and the two blocks are immediately 762 adjacent to each other, then the two free blocks are merged to form a single 763 larger block. 764 765* free_list - this is a structure pointing to previous and next elements in 766 this heap's free list. 767 It is only used in normal memory blocks; on ``malloc()`` to find a suitable 768 free block to allocate and on ``free()`` to add the newly freed element to 769 the free-list. 770 771* state - This field can have one of three values: ``FREE``, ``BUSY`` or 772 ``PAD``. 773 The former two are to indicate the allocation state of a normal memory block 774 and the latter is to indicate that the element structure is a dummy structure 775 at the end of the start-of-block padding, i.e. where the start of the data 776 within a block is not at the start of the block itself, due to alignment 777 constraints. 778 In that case, the pad header is used to locate the actual malloc element 779 header for the block. 780 781* pad - this holds the length of the padding present at the start of the block. 782 In the case of a normal block header, it is added to the address of the end 783 of the header to give the address of the start of the data area, i.e. the 784 value passed back to the application on a malloc. 785 Within a dummy header inside the padding, this same value is stored, and is 786 subtracted from the address of the dummy header to yield the address of the 787 actual block header. 788 789* size - the size of the data block, including the header itself. 790 791Memory Allocation 792^^^^^^^^^^^^^^^^^ 793 794On EAL initialization, all preallocated memory segments are setup as part of the 795malloc heap. This setup involves placing an :ref:`element header<malloc_elem>` 796with ``FREE`` at the start of each virtually contiguous segment of memory. 797The ``FREE`` element is then added to the ``free_list`` for the malloc heap. 798 799This setup also happens whenever memory is allocated at runtime (if supported), 800in which case newly allocated pages are also added to the heap, merging with any 801adjacent free segments if there are any. 802 803When an application makes a call to a malloc-like function, the malloc function 804will first index the ``lcore_config`` structure for the calling thread, and 805determine the NUMA node of that thread. 806The NUMA node is used to index the array of ``malloc_heap`` structures which is 807passed as a parameter to the ``heap_alloc()`` function, along with the 808requested size, type, alignment and boundary parameters. 809 810The ``heap_alloc()`` function will scan the free_list of the heap, and attempt 811to find a free block suitable for storing data of the requested size, with the 812requested alignment and boundary constraints. 813 814When a suitable free element has been identified, the pointer to be returned 815to the user is calculated. 816The cache-line of memory immediately preceding this pointer is filled with a 817struct malloc_elem header. 818Because of alignment and boundary constraints, there could be free space at 819the start and/or end of the element, resulting in the following behavior: 820 821#. Check for trailing space. 822 If the trailing space is big enough, i.e. > 128 bytes, then the free element 823 is split. 824 If it is not, then we just ignore it (wasted space). 825 826#. Check for space at the start of the element. 827 If the space at the start is small, i.e. <=128 bytes, then a pad header is 828 used, and the remaining space is wasted. 829 If, however, the remaining space is greater, then the free element is split. 830 831The advantage of allocating the memory from the end of the existing element is 832that no adjustment of the free list needs to take place - the existing element 833on the free list just has its size value adjusted, and the next/previous elements 834have their "prev"/"next" pointers redirected to the newly created element. 835 836In case when there is not enough memory in the heap to satisfy allocation 837request, EAL will attempt to allocate more memory from the system (if supported) 838and, following successful allocation, will retry reserving the memory again. In 839a multiprocessing scenario, all primary and secondary processes will synchronize 840their memory maps to ensure that any valid pointer to DPDK memory is guaranteed 841to be valid at all times in all currently running processes. 842 843Failure to synchronize memory maps in one of the processes will cause allocation 844to fail, even though some of the processes may have allocated the memory 845successfully. The memory is not added to the malloc heap unless primary process 846has ensured that all other processes have mapped this memory successfully. 847 848Any successful allocation event will trigger a callback, for which user 849applications and other DPDK subsystems can register. Additionally, validation 850callbacks will be triggered before allocation if the newly allocated memory will 851exceed threshold set by the user, giving a chance to allow or deny allocation. 852 853.. note:: 854 855 Any allocation of new pages has to go through primary process. If the 856 primary process is not active, no memory will be allocated even if it was 857 theoretically possible to do so. This is because primary's process map acts 858 as an authority on what should or should not be mapped, while each secondary 859 process has its own, local memory map. Secondary processes do not update the 860 shared memory map, they only copy its contents to their local memory map. 861 862Freeing Memory 863^^^^^^^^^^^^^^ 864 865To free an area of memory, the pointer to the start of the data area is passed 866to the free function. 867The size of the ``malloc_elem`` structure is subtracted from this pointer to get 868the element header for the block. 869If this header is of type ``PAD`` then the pad length is further subtracted from 870the pointer to get the proper element header for the entire block. 871 872From this element header, we get pointers to the heap from which the block was 873allocated and to where it must be freed, as well as the pointer to the previous 874and next elements. These next and previous elements are then checked to see if 875they are also ``FREE`` and are immediately adjacent to the current one, and if 876so, they are merged with the current element. This means that we can never have 877two ``FREE`` memory blocks adjacent to one another, as they are always merged 878into a single block. 879 880If deallocating pages at runtime is supported, and the free element encloses 881one or more pages, those pages can be deallocated and be removed from the heap. 882If DPDK was started with command-line parameters for preallocating memory 883(``-m`` or ``--socket-mem``), then those pages that were allocated at startup 884will not be deallocated. 885 886Any successful deallocation event will trigger a callback, for which user 887applications and other DPDK subsystems can register. 888