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* Intel® DPDK Loading and Launching: 44 The Intel® 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 Intel® 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 a module called 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 Intel® DPDK service layers such as the :ref:`Mempool Library <Mempool_Library>`. 74 75At this point, the Intel® 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. 137 138To access PCI memory, a kernel module called igb_uio provides a /dev/uioX device file 139that can be mmap'd to obtain access to PCI address space from the application. 140It uses 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 Intel® PDK 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 Intel® 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.. |linuxapp_launch| image:: img/linuxapp_launch.svg 216
