The chapter describes how to compile and run applications in an DPDK environment. It also provides a pointer to where sample applications are stored.
Note
Parts of this process can also be done using the setup script described in Chapter 6 of this document.
Once an DPDK target environment directory has been created (such as x86_64-native-linuxapp-gcc), it contains all libraries and header files required to build an application.
When compiling an application in the Linux* environment on the DPDK, the following variables must be exported:
The following is an example of creating the helloworld application, which runs in the DPDK Linux environment. This example may be found in the ${RTE_SDK}/examples directory.
The directory contains the main.c file. This file, when combined with the libraries in the DPDK target environment, calls the various functions to initialize the DPDK environment, then launches an entry point (dispatch application) for each core to be utilized. By default, the binary is generated in the build directory.
user@host:~/DPDK$ cd examples/helloworld/
user@host:~/DPDK/examples/helloworld$ export RTE_SDK=$HOME/DPDK
user@host:~/DPDK/examples/helloworld$ export RTE_TARGET=x86_64-native-linuxapp-gcc
user@host:~/DPDK/examples/helloworld$ make
CC main.o
LD helloworld
INSTALL-APP helloworld
INSTALL-MAP helloworld.map
user@host:~/DPDK/examples/helloworld$ ls build/app
helloworld helloworld.map
Note
In the above example, helloworld was in the directory structure of the DPDK. However, it could have been located outside the directory structure to keep the DPDK structure intact. In the following case, the helloworld application is copied to a new directory as a new starting point.
user@host:~$ export RTE_SDK=/home/user/DPDK
user@host:~$ cp -r $(RTE_SDK)/examples/helloworld my_rte_app
user@host:~$ cd my_rte_app/
user@host:~$ export RTE_TARGET=x86_64-native-linuxapp-gcc
user@host:~/my_rte_app$ make
CC main.o
LD helloworld
INSTALL-APP helloworld
INSTALL-MAP helloworld.map
Warning
The UIO drivers and hugepages must be setup prior to running an application.
Warning
Any ports to be used by the application must be already bound to an appropriate kernel module, as described in Section 3.5, prior to running the application.
The application is linked with the DPDK target environment’s Environmental Abstraction Layer (EAL) library, which provides some options that are generic to every DPDK application.
The following is the list of options that can be given to the EAL:
./rte-app -c COREMASK -n NUM [-b <domain:bus:devid.func>] [--socket-mem=MB,...] [-m MB] [-r NUM] [-v] [--file-prefix] [--proc-type <primary|secondary|auto>] [-- xen-dom0]
The EAL options are as follows:
The -c and the -n options are mandatory; the others are optional.
Copy the DPDK application binary to your target, then run the application as follows (assuming the platform has four memory channels per processor socket, and that cores 0-3 are present and are to be used for running the application):
user@target:~$ ./helloworld -c f -n 4
Note
The –proc-type and –file-prefix EAL options are used for running multiple DPDK processes. See the “Multi-process Sample Application” chapter in the DPDK Sample Applications User Guide and the DPDK Programmers Guide for more details.
The coremask parameter is always mandatory for DPDK applications. Each bit of the mask corresponds to the equivalent logical core number as reported by Linux. Since these logical core numbers, and their mapping to specific cores on specific NUMA sockets, can vary from platform to platform, it is recommended that the core layout for each platform be considered when choosing the coremask to use in each case.
On initialization of the EAL layer by an DPDK application, the logical cores to be used and their socket location are displayed. This information can also be determined for all cores on the system by examining the /proc/cpuinfo file, for example, by running cat /proc/cpuinfo. The physical id attribute listed for each processor indicates the CPU socket to which it belongs. This can be useful when using other processors to understand the mapping of the logical cores to the sockets.
Note
A more graphical view of the logical core layout may be obtained using the lstopo Linux utility. On Fedora* Linux, this may be installed and run using the following command:
sudo yum install hwloc
./lstopo
Warning
The logical core layout can change between different board layouts and should be checked before selecting an application coremask.
When running an application, it is recommended to use the same amount of memory as that allocated for hugepages. This is done automatically by the DPDK application at startup, if no -m or –socket-mem parameter is passed to it when run.
If more memory is requested by explicitly passing a -m or –socket-mem value, the application fails. However, the application itself can also fail if the user requests less memory than the reserved amount of hugepage-memory, particularly if using the -m option. The reason is as follows. Suppose the system has 1024 reserved 2 MB pages in socket 0 and 1024 in socket 1. If the user requests 128 MB of memory, the 64 pages may not match the constraints:
The socket-mem option can be used to request specific amounts of memory for specific sockets. This is accomplished by supplying the –socket-mem flag followed by amounts of memory requested on each socket, for example, supply –socket-mem=0,512 to try and reserve 512 MB for socket 1 only. Similarly, on a four socket system, to allocate 1 GB memory on each of sockets 0 and 2 only, the parameter –socket-mem=1024,0,1024 can be used. No memory will be reserved on any CPU socket that is not explicitly referenced, for example, socket 3 in this case. If the DPDK cannot allocate enough memory on each socket, the EAL initialization fails.
Additional sample applications are included in the ${RTE_SDK}/examples directory. These sample applications may be built and run in a manner similar to that described in earlier sections in this manual. In addition, see the DPDK Sample Applications User Guide for a description of the application, specific instructions on compilation and execution and some explanation of the code.
In addition, there are two other applications that are built when the libraries are created. The source files for these are in the DPDK/app directory and are called test and testpmd. Once the libraries are created, they can be found in the build/app directory.