1.. BSD LICENSE 2 Copyright(c) 2010-2014 Intel Corporation. All rights reserved. 3 All rights reserved. 4 5 Redistribution and use in source and binary forms, with or without 6 modification, are permitted provided that the following conditions 7 are met: 8 9 * Redistributions of source code must retain the above copyright 10 notice, this list of conditions and the following disclaimer. 11 * Redistributions in binary form must reproduce the above copyright 12 notice, this list of conditions and the following disclaimer in 13 the documentation and/or other materials provided with the 14 distribution. 15 * Neither the name of Intel Corporation nor the names of its 16 contributors may be used to endorse or promote products derived 17 from this software without specific prior written permission. 18 19 THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS 20 "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT 21 LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR 22 A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT 23 OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, 24 SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT 25 LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, 26 DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY 27 THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT 28 (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE 29 OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. 30 31.. _Environment_Abstraction_Layer: 32 33Environment Abstraction Layer 34============================= 35 36The Environment Abstraction Layer (EAL) is responsible for gaining access to low-level resources such as hardware and memory space. 37It provides a generic interface that hides the environment specifics from the applications and libraries. 38It is the responsibility of the initialization routine to decide how to allocate these resources 39(that is, memory space, PCI devices, timers, consoles, and so on). 40 41Typical services expected from the EAL are: 42 43* DPDK Loading and Launching: 44 The DPDK and its application are linked as a single application and must be loaded by some means. 45 46* Core Affinity/Assignment Procedures: 47 The EAL provides mechanisms for assigning execution units to specific cores as well as creating execution instances. 48 49* System Memory Reservation: 50 The EAL facilitates the reservation of different memory zones, for example, physical memory areas for device interactions. 51 52* PCI Address Abstraction: The EAL provides an interface to access PCI address space. 53 54* Trace and Debug Functions: Logs, dump_stack, panic and so on. 55 56* Utility Functions: Spinlocks and atomic counters that are not provided in libc. 57 58* CPU Feature Identification: Determine at runtime if a particular feature, for example, Intel® AVX is supported. 59 Determine if the current CPU supports the feature set that the binary was compiled for. 60 61* Interrupt Handling: Interfaces to register/unregister callbacks to specific interrupt sources. 62 63* Alarm Functions: Interfaces to set/remove callbacks to be run at a specific time. 64 65EAL in a Linux-userland Execution Environment 66--------------------------------------------- 67 68In a Linux user space environment, the DPDK application runs as a user-space application using the pthread library. 69PCI information about devices and address space is discovered through the /sys kernel interface and through kernel modules such as uio_pci_generic, or igb_uio. 70Refer to the UIO: User-space drivers documentation in the Linux kernel. This memory is mmap'd in the application. 71 72The EAL performs physical memory allocation using mmap() in hugetlbfs (using huge page sizes to increase performance). 73This memory is exposed to DPDK service layers such as the :ref:`Mempool Library <Mempool_Library>`. 74 75At this point, the DPDK services layer will be initialized, then through pthread setaffinity calls, 76each execution unit will be assigned to a specific logical core to run as a user-level thread. 77 78The time reference is provided by the CPU Time-Stamp Counter (TSC) or by the HPET kernel API through a mmap() call. 79 80Initialization and Core Launching 81~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ 82 83Part of the initialization is done by the start function of glibc. 84A check is also performed at initialization time to ensure that the micro architecture type chosen in the config file is supported by the CPU. 85Then, the main() function is called. The core initialization and launch is done in rte_eal_init() (see the API documentation). 86It consist of calls to the pthread library (more specifically, pthread_self(), pthread_create(), and pthread_setaffinity_np()). 87 88.. _pg_figure_2: 89 90**Figure 2. EAL Initialization in a Linux Application Environment** 91 92.. image3_png has been replaced 93 94|linuxapp_launch| 95 96.. note:: 97 98 Initialization of objects, such as memory zones, rings, memory pools, lpm tables and hash tables, 99 should be done as part of the overall application initialization on the master lcore. 100 The creation and initialization functions for these objects are not multi-thread safe. 101 However, once initialized, the objects themselves can safely be used in multiple threads simultaneously. 102 103Multi-process Support 104~~~~~~~~~~~~~~~~~~~~~ 105 106The Linuxapp EAL allows a multi-process as well as a multi-threaded (pthread) deployment model. 107See chapter 2.20 108:ref:`Multi-process Support <Multi-process_Support>` for more details. 109 110Memory Mapping Discovery and Memory Reservation 111~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ 112 113The allocation of large contiguous physical memory is done using the hugetlbfs kernel filesystem. 114The EAL provides an API to reserve named memory zones in this contiguous memory. 115The physical address of the reserved memory for that memory zone is also returned to the user by the memory zone reservation API. 116 117.. note:: 118 119 Memory reservations done using the APIs provided by the rte_malloc library are also backed by pages from the hugetlbfs filesystem. 120 However, physical address information is not available for the blocks of memory allocated in this way. 121 122Xen Dom0 support without hugetbls 123~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ 124 125The existing memory management implementation is based on the Linux kernel hugepage mechanism. 126However, Xen Dom0 does not support hugepages, so a new Linux kernel module rte_dom0_mm is added to workaround this limitation. 127 128The EAL uses IOCTL interface to notify the Linux kernel module rte_dom0_mm to allocate memory of specified size, 129and get all memory segments information from the module, 130and the EAL uses MMAP interface to map the allocated memory. 131For each memory segment, the physical addresses are contiguous within it but actual hardware addresses are contiguous within 2MB. 132 133PCI Access 134~~~~~~~~~~ 135 136The EAL uses the /sys/bus/pci utilities provided by the kernel to scan the content on the PCI bus. 137To access PCI memory, a kernel module called uio_pci_generic provides a /dev/uioX device file 138and resource files in /sys 139that can be mmap'd to obtain access to PCI address space from the application. 140The DPDK-specific igb_uio module can also be used for this. Both drivers use the uio kernel feature (userland driver). 141 142Per-lcore and Shared Variables 143~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ 144 145.. note:: 146 147 lcore refers to a logical execution unit of the processor, sometimes called a hardware *thread*. 148 149Shared variables are the default behavior. 150Per-lcore variables are implemented using *Thread Local Storage* (TLS) to provide per-thread local storage. 151 152Logs 153~~~~ 154 155A logging API is provided by EAL. 156By default, in a Linux application, logs are sent to syslog and also to the console. 157However, the log function can be overridden by the user to use a different logging mechanism. 158 159Trace and Debug Functions 160^^^^^^^^^^^^^^^^^^^^^^^^^ 161 162There are some debug functions to dump the stack in glibc. 163The rte_panic() function can voluntarily provoke a SIG_ABORT, 164which can trigger the generation of a core file, readable by gdb. 165 166CPU Feature Identification 167~~~~~~~~~~~~~~~~~~~~~~~~~~ 168 169The EAL can query the CPU at runtime (using the rte_cpu_get_feature() function) to determine which CPU features are available. 170 171User Space Interrupt and Alarm Handling 172~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ 173 174The EAL creates a host thread to poll the UIO device file descriptors to detect the interrupts. 175Callbacks can be registered or unregistered by the EAL functions for a specific interrupt event 176and are called in the host thread asynchronously. 177The EAL also allows timed callbacks to be used in the same way as for NIC interrupts. 178 179.. note:: 180 181 The only interrupts supported by the DPDK Poll-Mode Drivers are those for link status change, 182 i.e. link up and link down notification. 183 184Blacklisting 185~~~~~~~~~~~~ 186 187The EAL PCI device blacklist functionality can be used to mark certain NIC ports as blacklisted, 188so they are ignored by the DPDK. 189The ports to be blacklisted are identified using the PCIe* description (Domain:Bus:Device.Function). 190 191Misc Functions 192~~~~~~~~~~~~~~ 193 194Locks and atomic operations are per-architecture (i686 and x86_64). 195 196Memory Segments and Memory Zones (memzone) 197------------------------------------------ 198 199The mapping of physical memory is provided by this feature in the EAL. 200As physical memory can have gaps, the memory is described in a table of descriptors, 201and each descriptor (called rte_memseg ) describes a contiguous portion of memory. 202 203On top of this, the memzone allocator's role is to reserve contiguous portions of physical memory. 204These zones are identified by a unique name when the memory is reserved. 205 206The rte_memzone descriptors are also located in the configuration structure. 207This structure is accessed using rte_eal_get_configuration(). 208The lookup (by name) of a memory zone returns a descriptor containing the physical address of the memory zone. 209 210Memory zones can be reserved with specific start address alignment by supplying the align parameter 211(by default, they are aligned to cache line size). 212The alignment value should be a power of two and not less than the cache line size (64 bytes). 213Memory zones can also be reserved from either 2 MB or 1 GB hugepages, provided that both are available on the system. 214 215 216Multiple pthread 217---------------- 218 219DPDK usually pins one pthread per core to avoid the overhead of task switching. 220This allows for significant performance gains, but lacks flexibility and is not always efficient. 221 222Power management helps to improve the CPU efficiency by limiting the CPU runtime frequency. 223However, alternately it is possible to utilize the idle cycles available to take advantage of 224the full capability of the CPU. 225 226By taking advantage of cgroup, the CPU utilization quota can be simply assigned. 227This gives another way to improve the CPU efficienct, however, there is a prerequisite; 228DPDK must handle the context switching between multiple pthreads per core. 229 230For further flexibility, it is useful to set pthread affinity not only to a CPU but to a CPU set. 231 232EAL pthread and lcore Affinity 233~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ 234 235The term "lcore" refers to an EAL thread, which is really a Linux/FreeBSD pthread. 236"EAL pthreads" are created and managed by EAL and execute the tasks issued by *remote_launch*. 237In each EAL pthread, there is a TLS (Thread Local Storage) called *_lcore_id* for unique identification. 238As EAL pthreads usually bind 1:1 to the physical CPU, the *_lcore_id* is typically equal to the CPU ID. 239 240When using multiple pthreads, however, the binding is no longer always 1:1 between an EAL pthread and a specified physical CPU. 241The EAL pthread may have affinity to a CPU set, and as such the *_lcore_id* will not be the same as the CPU ID. 242For this reason, there is an EAL long option '--lcores' defined to assign the CPU affinity of lcores. 243For a specified lcore ID or ID group, the option allows setting the CPU set for that EAL pthread. 244 245The format pattern: 246 --lcores='<lcore_set>[@cpu_set][,<lcore_set>[@cpu_set],...]' 247 248'lcore_set' and 'cpu_set' can be a single number, range or a group. 249 250A number is a "digit([0-9]+)"; a range is "<number>-<number>"; a group is "(<number|range>[,<number|range>,...])". 251 252If a '\@cpu_set' value is not supplied, the value of 'cpu_set' will default to the value of 'lcore_set'. 253 254 :: 255 256 For example, "--lcores='1,2@(5-7),(3-5)@(0,2),(0,6),7-8'" which means start 9 EAL thread; 257 lcore 0 runs on cpuset 0x41 (cpu 0,6); 258 lcore 1 runs on cpuset 0x2 (cpu 1); 259 lcore 2 runs on cpuset 0xe0 (cpu 5,6,7); 260 lcore 3,4,5 runs on cpuset 0x5 (cpu 0,2); 261 lcore 6 runs on cpuset 0x41 (cpu 0,6); 262 lcore 7 runs on cpuset 0x80 (cpu 7); 263 lcore 8 runs on cpuset 0x100 (cpu 8). 264 265Using this option, for each given lcore ID, the associated CPUs can be assigned. 266It's also compatible with the pattern of corelist('-l') option. 267 268non-EAL pthread support 269~~~~~~~~~~~~~~~~~~~~~~~ 270 271It is possible to use the DPDK execution context with any user pthread (aka. Non-EAL pthreads). 272In 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*. 273Some 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). 274 275All these impacts are mentioned in :ref:`known_issue_label` section. 276 277Public Thread API 278~~~~~~~~~~~~~~~~~ 279 280There are two public APIs ``rte_thread_set_affinity()`` and ``rte_pthread_get_affinity()`` introduced for threads. 281When they're used in any pthread context, the Thread Local Storage(TLS) will be set/get. 282 283Those TLS include *_cpuset* and *_socket_id*: 284 285* *_cpuset* stores the CPUs bitmap to which the pthread is affinitized. 286 287* *_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 SOCKTE_ID_ANY. 288 289 290.. _known_issue_label: 291 292Known Issues 293~~~~~~~~~~~~ 294 295+ rte_mempool 296 297 The rte_mempool uses a per-lcore cache inside the mempool. 298 For non-EAL pthreads, ``rte_lcore_id()`` will not return a valid number. 299 So for now, when rte_mempool is used with non-EAL pthreads, the put/get operations will bypass the mempool cache and there is a performance penalty because of this bypass. 300 Support for non-EAL mempool cache is currently being enabled. 301 302+ rte_ring 303 304 rte_ring supports multi-producer enqueue and multi-consumer dequeue. 305 However, it is non-preemptive, this has a knock on effect of making rte_mempool non-preemtable. 306 307 .. note:: 308 309 The "non-preemptive" constraint means: 310 311 - a pthread doing multi-producers enqueues on a given ring must not 312 be preempted by another pthread doing a multi-producer enqueue on 313 the same ring. 314 - a pthread doing multi-consumers dequeues on a given ring must not 315 be preempted by another pthread doing a multi-consumer dequeue on 316 the same ring. 317 318 Bypassing this constraint it may cause the 2nd pthread to spin until the 1st one is scheduled again. 319 Moreover, if the 1st pthread is preempted by a context that has an higher priority, it may even cause a dead lock. 320 321 This does not mean it cannot be used, simply, there is a need to narrow down the situation when it is used by multi-pthread on the same core. 322 323 1. It CAN be used for any single-producer or single-consumer situation. 324 325 2. It MAY be used by multi-producer/consumer pthread whose scheduling policy are all SCHED_OTHER(cfs). User SHOULD be aware of the performance penalty before using it. 326 327 3. It MUST not be used by multi-producer/consumer pthreads, whose scheduling policies are SCHED_FIFO or SCHED_RR. 328 329 ``RTE_RING_PAUSE_REP_COUNT`` is defined for rte_ring to reduce contention. It's mainly for case 2, a yield is issued after number of times pause repeat. 330 331 It adds a sched_yield() syscall if the thread spins for too long while waiting on the other thread to finish its operations on the ring. 332 This gives the pre-empted thread a chance to proceed and finish with the ring enqueue/dequeue operation. 333 334+ rte_timer 335 336 Running ``rte_timer_manager()`` on a non-EAL pthread is not allowed. However, resetting/stopping the timer from a non-EAL pthread is allowed. 337 338+ rte_log 339 340 In non-EAL pthreads, there is no per thread loglevel and logtype, global loglevels are used. 341 342+ misc 343 344 The debug statistics of rte_ring, rte_mempool and rte_timer are not supported in a non-EAL pthread. 345 346cgroup control 347~~~~~~~~~~~~~~ 348 349The 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). 350We expect only 50% of CPU spend on packet IO. 351 352 .. code:: 353 354 mkdir /sys/fs/cgroup/cpu/pkt_io 355 mkdir /sys/fs/cgroup/cpuset/pkt_io 356 357 echo $cpu > /sys/fs/cgroup/cpuset/cpuset.cpus 358 359 echo $t0 > /sys/fs/cgroup/cpu/pkt_io/tasks 360 echo $t0 > /sys/fs/cgroup/cpuset/pkt_io/tasks 361 362 echo $t1 > /sys/fs/cgroup/cpu/pkt_io/tasks 363 echo $t1 > /sys/fs/cgroup/cpuset/pkt_io/tasks 364 365 cd /sys/fs/cgroup/cpu/pkt_io 366 echo 100000 > pkt_io/cpu.cfs_period_us 367 echo 50000 > pkt_io/cpu.cfs_quota_us 368 369 370.. |linuxapp_launch| image:: img/linuxapp_launch.* 371