2. System Requirements

2.3.2.1. Reserving Hugepages for DPDK Use

The allocation of hugepages should be done at boot time or as soon as possible after system boot to prevent memory from being fragmented in physical memory. To reserve hugepages at boot time, a parameter is passed to the Linux kernel on the kernel command line.

For 2 MB pages, just pass the hugepages option to the kernel. For example, to reserve 1024 pages of 2 MB, use:

hugepages=1024

For other hugepage sizes, for example 1G pages, the size must be specified explicitly and can also be optionally set as the default hugepage size for the system. For example, to reserve 4G of hugepage memory in the form of four 1G pages, the following options should be passed to the kernel:

default_hugepagesz=1G hugepagesz=1G hugepages=4

In the case of a dual-socket NUMA system, the number of hugepages reserved at boot time is generally divided equally between the two sockets (on the assumption that sufficient memory is present on both sockets).

See the Documentation/kernel-parameters.txt file in your Linux source tree for further details of these and other kernel options.

Alternative:

For 2 MB pages, there is also the option of allocating hugepages after the system has booted. This is done by echoing the number of hugepages required to a nr_hugepages file in the /sys/devices/ directory. For a single-node system, the command to use is as follows (assuming that 1024 pages are required):

echo 1024 > /sys/kernel/mm/hugepages/hugepages-2048kB/nr_hugepages

On a NUMA machine, pages should be allocated explicitly on separate nodes:

echo 1024 > /sys/devices/system/node/node0/hugepages/hugepages-2048kB/nr_hugepages
echo 1024 > /sys/devices/system/node/node1/hugepages/hugepages-2048kB/nr_hugepages

2.3.2.2. Using Hugepages with the DPDK

Once the hugepage memory is reserved, to make the memory available for DPDK use, perform the following steps:

mkdir /mnt/huge
mount -t hugetlbfs nodev /mnt/huge

The mount point can be made permanent across reboots, by adding the following line to the /etc/fstab file:

nodev /mnt/huge hugetlbfs defaults 0 0

For 1GB pages, the page size must be specified as a mount option:

nodev /mnt/huge_1GB hugetlbfs pagesize=1GB 0 0

2.3.3.1. Enabling Xen Dom0 Mode in the DPDK

By default, Xen Dom0 mode is disabled in the DPDK build configuration files. To support Xen Dom0, the CONFIG_RTE_LIBRTE_XEN_DOM0 setting should be changed to “y”, which enables the Xen Dom0 mode at compile time.

Furthermore, the CONFIG_RTE_EAL_ALLOW_INV_SOCKET_ID setting should also be changed to “y” in the case of the wrong socket ID being received.

2.3.3.2. Loading the DPDK rte_dom0_mm Module

To run any DPDK application on Xen Dom0, the rte_dom0_mm module must be loaded into the running kernel with rsv_memsize option. The module is found in the kmod sub-directory of the DPDK target directory. This module should be loaded using the insmod command as shown below (assuming that the current directory is the DPDK target directory):

sudo insmod kmod/rte_dom0_mm.ko rsv_memsize=X

The value X cannot be greater than 4096(MB).

2.3.3.3. Configuring Memory for DPDK Use

After the rte_dom0_mm.ko kernel module has been loaded, the user must configure the memory size for DPDK usage. This is done by echoing the memory size to a memsize file in the /sys/devices/ directory. Use the following command (assuming that 2048 MB is required):

echo 2048 > /sys/kernel/mm/dom0-mm/memsize-mB/memsize

The user can also check how much memory has already been used:

cat /sys/kernel/mm/dom0-mm/memsize-mB/memsize_rsvd

Xen Domain0 does not support NUMA configuration, as a result the --socket-mem command line option is invalid for Xen Domain0.

2.3.3.4. Running the DPDK Application on Xen Domain0

To run the DPDK application on Xen Domain0, an extra command line option --xen-dom0 is required.