3. Compiling the DPDK Target from Source

3.1. Prerequisites

The following FreeBSD packages are required to build DPDK:

  • meson
  • ninja
  • pkgconf
  • py38-pyelftools

These can be installed using (as root):

pkg install meson pkgconf py38-pyelftools

To compile the required kernel modules for memory management and working with physical NIC devices, the kernel sources for FreeBSD also need to be installed. If not already present on the system, these can be installed via commands like the following, for FreeBSD 12.1 on x86_64:

fetch http://ftp.freebsd.org/pub/FreeBSD/releases/amd64/12.1-RELEASE/src.txz
tar -C / -xJvf src.txz

Individual drivers may have additional requirements. Consult the relevant driver guide for any driver-specific requirements of interest.

3.2. Building DPDK

The following commands can be used to build and install DPDK on a system. The final, install, step generally needs to be run as root:

meson build
cd build
ninja install

This will install the DPDK libraries and drivers to /usr/local/lib with a pkg-config file libdpdk.pc installed to /usr/local/lib/pkgconfig. The DPDK test applications, such as dpdk-testpmd are installed to /usr/local/bin. To use these applications, it is recommended that the contigmem and nic_uio kernel modules be loaded first, as described in the next section.


It is recommended that pkg-config be used to query information about the compiler and linker flags needed to build applications against DPDK. In some cases, the path /usr/local/lib/pkgconfig may not be in the default search paths for .pc files, which means that queries for DPDK information may fail. This can be fixed by setting the appropriate path in PKG_CONFIG_PATH environment variable.

3.3. Loading the DPDK contigmem Module

To run a DPDK application, physically contiguous memory is required. In the absence of non-transparent superpages, the included sources for the contigmem kernel module provides the ability to present contiguous blocks of memory for the DPDK to use. The contigmem module must be loaded into the running kernel before any DPDK is run. Once DPDK is installed on the system, the module can be found in the /boot/modules directory.

The amount of physically contiguous memory along with the number of physically contiguous blocks to be reserved by the module can be set at runtime prior to module loading using:

kenv hw.contigmem.num_buffers=n
kenv hw.contigmem.buffer_size=m

The kernel environment variables can also be specified during boot by placing the following in /boot/loader.conf:


The variables can be inspected using the following command:

sysctl -a hw.contigmem

Where n is the number of blocks and m is the size in bytes of each area of contiguous memory. A default of two buffers of size 1073741824 bytes (1 Gigabyte) each is set during module load if they are not specified in the environment.

The module can then be loaded using kldload:

kldload contigmem

It is advisable to include the loading of the contigmem module during the boot process to avoid issues with potential memory fragmentation during later system up time. This can be achieved by placing lines similar to the following into /boot/loader.conf:



The contigmem_load directive should be placed after any definitions of hw.contigmem.num_buffers and hw.contigmem.buffer_size if the default values are not to be used.

An error such as:

kldload: can't load <build_dir>/kernel/freebsd/contigmem.ko:
         Exec format error

is generally attributed to not having enough contiguous memory available and can be verified via dmesg or /var/log/messages:

kernel: contigmalloc failed for buffer <n>

To avoid this error, reduce the number of buffers or the buffer size.

3.4. Loading the DPDK nic_uio Module

After loading the contigmem module, the nic_uio module must also be loaded into the running kernel prior to running any DPDK application, e.g. using:

kldload nic_uio


If the ports to be used are currently bound to a existing kernel driver then the hw.nic_uio.bdfs sysctl value will need to be set before loading the module. Setting this value is described in the next section below.

Currently loaded modules can be seen by using the kldstat command and a module can be removed from the running kernel by using kldunload <module_name>.

To load the module during boot place the following into /boot/loader.conf:



nic_uio_load="YES" must appear after the contigmem_load directive, if it exists.

By default, the nic_uio module will take ownership of network ports if they are recognized DPDK devices and are not owned by another module. However, since the FreeBSD kernel includes support, either built-in, or via a separate driver module, for most network card devices, it is likely that the ports to be used are already bound to a driver other than nic_uio. The following sub-section describe how to query and modify the device ownership of the ports to be used by DPDK applications.

3.4.1. Binding Network Ports to the nic_uio Module

Device ownership can be viewed using the pciconf -l command. The example below shows four Intel® 82599 network ports under if_ixgbe module ownership.

pciconf -l
ix0@pci0:1:0:0: class=0x020000 card=0x00038086 chip=0x10fb8086 rev=0x01 hdr=0x00
ix1@pci0:1:0:1: class=0x020000 card=0x00038086 chip=0x10fb8086 rev=0x01 hdr=0x00
ix2@pci0:2:0:0: class=0x020000 card=0x00038086 chip=0x10fb8086 rev=0x01 hdr=0x00
ix3@pci0:2:0:1: class=0x020000 card=0x00038086 chip=0x10fb8086 rev=0x01 hdr=0x00

The first column constitutes three components:

  1. Device name: ixN
  2. Unit name: pci0
  3. Selector (Bus:Device:Function): 1:0:0

Where no driver is associated with a device, the device name will be none.

By default, the FreeBSD kernel will include built-in drivers for the most common devices; a kernel rebuild would normally be required to either remove the drivers or configure them as loadable modules.

To avoid building a custom kernel, the nic_uio module can detach a network port from its current device driver. This is achieved by setting the hw.nic_uio.bdfs kernel environment variable prior to loading nic_uio, as follows:

kenv hw.nic_uio.bdfs="b:d:f,b:d:f,..."

Where a comma separated list of selectors is set, the list must not contain any whitespace.

For example to re-bind ix2@pci0:2:0:0 and ix3@pci0:2:0:1 to the nic_uio module upon loading, use the following command:

kenv hw.nic_uio.bdfs="2:0:0,2:0:1"

The variable can also be specified during boot by placing the following into /boot/loader.conf, before the previously-described nic_uio_load line - as shown:


3.4.2. Binding Network Ports Back to their Original Kernel Driver

If the original driver for a network port has been compiled into the kernel, it is necessary to reboot FreeBSD to restore the original device binding. Before doing so, update or remove the hw.nic_uio.bdfs in /boot/loader.conf.

If rebinding to a driver that is a loadable module, the network port binding can be reset without rebooting. To do so, unload both the target kernel module and the nic_uio module, modify or clear the hw.nic_uio.bdfs kernel environment (kenv) value, and reload the two drivers - first the original kernel driver, and then the nic_uio driver. Note: the latter does not need to be reloaded unless there are ports that are still to be bound to it.

Example commands to perform these steps are shown below:

kldunload nic_uio
kldunload <original_driver>

# To clear the value completely:
kenv -u hw.nic_uio.bdfs

# To update the list of ports to bind:
kenv hw.nic_uio.bdfs="b:d:f,b:d:f,..."

kldload <original_driver>

kldload nic_uio  # optional