Scenario - Using Open vSwitch w/ DPDK


Operators can choose to utilize DPDK-accelerated Open vSwitch instead of unaccelerated Open vSwitch or Linux Bridges for the Neutron virtual network infrastructure. This architecture is best suited for NFV workloads and requires careful consideration and planning before implementing. This document outlines how to set it up in your environment.


The current implementation of DPDK in OpenStack-Ansible is experimental and not production ready. There is no guarantee of upgradability or backwards compatibility between releases.


To enable DPDK on a Linux platform, ensure that VT-d/VT-x are enabled for Intel processors and AMD-V/AMD-Vi are enabled for AMD processors. Such features are typically enabled in the BIOS.

On an Intel platform, the following kernel parameters are required and can be added to the GRUB configuration:

GRUB_CMDLINE_LINUX="... iommu=pt intel_iommu=on"

On an AMD platform, use these parameters instead:

GRUB_CMDLINE_LINUX="... iommu=pt amd_iommu=on"

Update GRUB and reboot the host(s).

Hugepages are required for DPDK. Instances leveraging DPDK-accelerated Open vSwitch must be configured to use hugepages by way of flavor attributes. Those attributes and the configuration of hugepages are described in this guide.

CPU frequency should be set to maximum for optimal performance. Many hardware vendors set the energy saving properties in the BIOS that may need to be modified. Changing the CPU frequency using cpufreq or similar utilities to performance from ondemand is recommended.


The playbooks currently only support a single NIC interface for DPDK. Multiple ports per NIC are not yet supported but may be at a later time. This guide assumes the NIC is bound to NUMA node0, but the instructions can be modified for NICs bound to other NUMA nodes..

NUMA topology

Non-uniform memory access (NUMA) is a computer memory design used in multiprocessing. This guide cannot go into great depths about NUMA architecture. However, there are some configurations to be made that rely on the operator understanding NUMA characteristics of compute nodes hosting workloads using DPDK-accelerated Open vSwitch.

To view the NUMA topology of a particular system, use the numactl command shown here:

root@compute1:~# numactl --hardware
available: 2 nodes (0-1)
node 0 cpus: 0 1 2 3 4 5 6 7 16 17 18 19 20 21 22 23
node 0 size: 48329 MB
node 0 free: 31798 MB
node 1 cpus: 8 9 10 11 12 13 14 15 24 25 26 27 28 29 30 31
node 1 size: 48379 MB
node 1 free: 25995 MB
node distances:
node   0   1
  0:  10  20
  1:  20  10

The NUMA topology presented here corresponds to a host with 2x Intel Xeon 2450L processors with 96 GB of total RAM. The RAM is evenly split between the two NUMA nodes. Each CPU has 8 cores. With hyperthreading enabled, there are 16 threads per CPU for a total of 32 threads or cores presented to the operating system. It just so happens that this two-socket system has one NUMA node per socket, however, that will not always be the case. Consult your system’s documentation for information unique to your system.

The first eight cores/cpus in the list for a given NUMA node can be considered physical cores in the CPU. For NUMA node0, this would be cores 0-7. The other eight cores, 16-23, are considered virtual sibling cores and are presented when hyperthreading is enabled. The physical-to-virtual mapping can be determined with the following commands:

root@compute1:~# for cpu in {0..7}; do cat /sys/devices/system/cpu/"cpu"$cpu/topology/thread_siblings_list; done

root@compute1:~# for cpu in {8..15}; do cat /sys/devices/system/cpu/"cpu"$cpu/topology/thread_siblings_list; done

A PCI slot typically corresponds to a single NUMA node. For optimal performance, a DPDK NIC and any instance utilizing the NIC should be restricted to the same NUMA node and its respective memory. Ensuring this behavior requires the use of flavors, host aggregates, and special kernel parameters and Open vSwitch/DPDK configuration settings.

In this example, a single 10G NIC installed in PCI slot 2 is bound to NUMA node0. Ideally, any instances utilizing the NIC would be limited to cores and memory associated with NUMA node0. This means cores 0-7 and 16-23, and up to 48GB of RAM. In reality, however, some cores and RAM from NUMA node0 will be reserved and made unavailable to instances. In addition, cores 8-15 and 24-31 associated with NUMA node1 should be made unavailable to instances. The configuration to do just that will be covered later in this guide.

It is considered good practice to reserve a single physical core and its respective virtual sibling from each NUMA node for normal (non-DPDK) operating system functions. In addition, at least one physical core (and sibling) from each NUMA node should be reserved for DPDK poll mode driver (PMD) functions, even when a NIC(s) is bound to a single NUMA node. The remaining cores can be reserved for virtual machine instances.

In this example, the breakdown would resemble the following:

` | Reserved Cores         | Purpose               | node0     | node1 | | ---------------------- | --------------------- | --------- | ----- | | 0,8,16,24              | Host Operating System | 0,16      | 8,24  | | 1,9,17,25              | DPDK PMDs             | 1,17      | 9,25  | | 2-7,18-23              | Virtual Machines      | 2-7,18-23 | N/A   | `

The variables are overrides used to define this configuration are discussed in the following sections.

Hugepage configuration

DPDK requires the configuration of hugepages, which is a mechanism by which the Linux kernel can partition and address larger amounts of memory beyond the basic page unit (4096 bytes). Huge pages are blocks of contiguous memory that commonly come in 2MB and 1G sizes. The page tables used by 2MB pages are suitable for managing multiple gigabytes of memory, whereas the page tables of 1GB pages are preferred for scaling to terabytes of memory. DPDK requires the use of 1GB pages.

A typical x86 system will have a Huge Page Size of 2048 kBytes (2MB). The default huge page size may be found by looking at the output of /proc/meminfo:

# cat /proc/meminfo | grep Hugepagesize
Hugepagesize: 2048 kB

The number of Hugepages can be allocated at runtime by modifying /proc/sys/vm/nr_hugepages or by using the sysctl command.

To view the current setting using the /proc entry:

# cat /proc/sys/vm/nr_hugepages

To view the current setting using the sysctl command:

# sysctl vm.nr_hugepages
vm.nr_hugepages = 0

To set the number of huge pages using /proc entry:

# echo 5 > /proc/sys/vm/nr_hugepages

To set the number of hugepages using sysctl:

# sysctl -w vm.nr_hugepages=5
vm.nr_hugepages = 5

It may be necessary to reboot to be able to allocate the number of hugepages that is needed. This is due to hugepages requiring large areas of contiguous physical memory.

When 1G hugepages are used, they must be configured at boot time. The amount of 1G hugepages that should be created will vary based on a few factors, including:

  • The total amount of RAM available in the system

  • The amount of RAM required for the planned number of instances

  • The number of NUMA nodes that will be used

The NUMA topology presented here corresponds to a host with 2x Intel Xeon 2450L processors with 96GB of total RAM. The RAM is evenly split between the two NUMA nodes. A DPDK NIC will be associated with a single NUMA node, and for optimal performance any instance utilizing the DPDK NIC should be limited to the same cores and memory associated with the NUMA node. On this example system, both DPDK and instances can only utilize up to the 48GB of RAM associated with NUMA node0, though some of that RAM will be utilized by the OS and other tasks.

Of the 48GB of RAM available on NUMA node0, 32GB will be reserved for 1GB hugepages to be consumed by DPDK PMDs and instances. Configuring hugepages using kernel parameters results in the defined number of hugepages to be split evenly across NUMA nodes. With the following kernel parameter, each NUMA node will be assigned 32x 1G hugepages:

GRUB_CMDLINE_LINUX="... hugepagesz=1G hugepages=64"

Hugepages can be adjusted at runtime if necessary, but doing so is outside the scope of this guide.

OpenStack-Ansible variables and overrides

The ability to pin instances to certain cores is not new, and can be accomplished using the vcpu_pin_set override seen here:

    vcpu_pin_set: 2-7,18-23

This change can be added to the user_overrides.yml file for global implementation, or to individual nodes in the openstack_user_config.yml file as shown here:

          vcpu_pin_set: 2-7,18-23

Cores reserved for host operating system functions (non-DPDK) must be converted to a hexidecimal mask and defined using the ovs_dpdk_lcore_mask override. To convert to a hex mask you must first establish the binary mask of chosen cores using the following table:

` | 31 | 30 | . | 24 | 23 | . | 17 | 16 | 15 | . | 9  | 8  | 7  | . | 1  | 0  | | -- | -- | - | -- | -- | - | -- | -- | -- | - | -- | -- | -- | - | -- | -- | | 0  | 0  | . | 1  | 0  | . | 0  | 1  | 0  | . | 0  | 1  | 0  | . | 0  | 1  | `

The ellipses represent cores not shown. The binary mask for cores 0,8,16,24 can be determined in the following way:


The hexidecimal representation of that binary value is 0x1010101. Set the ovs_dpdk_lcore_mask override accordingly in the user_variables.yml file or openstack_user_config.yml:

ovs_dpdk_lcore_mask: 1010101

The mask for cores 1,9,17,25 reserved for DPDK PMDs can be determined in a similar fashion. The table would resemble the following:

` | 31 | 30 | . | 25 | 24 | . | 17 | 16 | 15 | . | 9  | 8  | 7  | . | 1  | 0  | | -- | -- | - | -- | -- | - | -- | -- | -- | - | -- | -- | -- | - | -- | -- | | 0  | 0  | . | 1  | 0  | . | 1  | 0  | 0  | . | 1  | 0  | 0  | . | 1  | 0  | `

The ellipses represent cores not shown. The binary mask for cores 1,9,17,254 can be determined in the following way:


The hexidecimal representation of that binary value is 0x2020202. Set the ovs_dpdk_pmd_cpu_mask override accordingly in the user_variables.yml file or openstack_user_config.yml:

ovs_dpdk_pmd_cpu_mask: 2020202

Additional variables should be set, including:

  • ovs_dpdk_driver

  • ovs_dpdk_pci_addresses

  • ovs_dpdk_socket_mem

The default value for ovs_dpdk_driver is vfio-pci. Overrides can be set globally or on a per-host basis.


Please consult the DPDK Network Interface Controller Driver documentation for more inforation on supported network drivers for DPDK.

The value for ovs_dpdk_pci_addresses is the PCI bus address of the NIC port(s) associated with the DPDK NIC. In this example, the DPDK NIC is identified as address 0000:03:00. The individual interfaces are 0000:03:00.0 and 0000:03:00.1, respectively. The variable ovs_dpdk_pci_addresses is a list, and both values can be defined like so:

  - 0000:03:00.0
  - 0000:03:00.1

The value for ovs_dpdk_socket_mem will vary based on the number of NUMA nodes, number of NICs per NUMA node, and the MTU. The default value assumes a single NUMA node and associates a single 1G hugepage to DPDK that can handle a 1500 MTU. When multiple NUMA nodes are available, even with a single NIC, the following should be set:

ovs_dpdk_socket_mem: "1024,1024"

For systems using a single NUMA node of a dual-NUMA system and a 9000 MTU, the following can be set:

ovs_dpdk_socket_mem: "3072,1024"

Determing socket memory required involves calculations that are out of the scope of this guide.

Flavor configuration

Instances that connect to a DPDK-accelerated Open vSwitch must be configured to utilize large (1G) hugepages by way of custom flavor attributes.

The hw:mem_page_size property can be set on a new or existing flavor to enable this functionality:

openstack flavor set m1.small --property hw:mem_page_size=large

NOTE: If small page size is used, or no page size is set, the interface may appear in the instance but will not be functional.

OpenStack-Ansible user variables

Create a group var file for your network hosts /etc/openstack_deploy/group_vars/network_hosts. It has to include:

# Ensure the openvswitch kernel module is loaded
  - name: "openvswitch"

Specify provider network definitions in your /etc/openstack_deploy/openstack_user_config.yml that define one or more Neutron provider bridges and related configuration:


Bridges specified here will be created automatically. If network_interface is defined, the interface will be placed into the bridge automatically as a DPDK-accelerated interface.

- network:
    container_bridge: "br-provider"
    container_type: "veth"
    type: "vlan"
    range: "101:200,301:400"
    net_name: "physnet1"
    network_interface: "eno49"
      - neutron_openvswitch_agent

A DPDK-accelerated bond interface can be created by specifying a list of member interfaces using network_bond_interfaces. The bond port will be created automatically and added to the respective bridge in OVS:

- network:
    container_bridge: "br-provider"
    container_type: "veth"
    type: "vlan"
    range: "101:200,301:400"
    net_name: "physnet1"
      - "0000:04:00.0"
      - "0000:04:00.1"
      - neutron_openvswitch_agent

Additional OVS bond parameters can be specified using the following keys:

  • bond_mode (Default: active-backup)

  • lacp (Default: off)

  • bond_downdelay (Default: 100)

  • bond_updelay (Default: 100)

- network:
    container_bridge: "br-provider"
    container_type: "veth"
    type: "vlan"
    range: "101:200,301:400"
    net_name: "physnet1"
      - "0000:04:00.0"
      - "0000:04:00.1"
    bond_mode: balance-tcp
    lacp: active
    bond_downdelay: 200
    bond_updelay: 200
      - neutron_openvswitch_agent

For more information on possible values, visit:

Set the following user variables in your /etc/openstack_deploy/user_variables.yml to enable the Open vSwitch driver and DPDK support:

neutron_plugin_type: ml2.ovs
neutron_ml2_drivers_type: "vlan"
  - router
  - metering

# Enable DPDK support
ovs_dpdk_support: True

# Add these overrides or set on per-host basis in openstack_user_config.yml
  - "0000:04:00.0"
  - "0000:04:00.1"
ovs_dpdk_lcore_mask: 1010101
ovs_dpdk_pmd_cpu_mask: 2020202
ovs_dpdk_socket_mem: "1024,1024"


Overlay networks are not supported on DPDK-enabled nodes at this time.


Once the playbooks have been run and OVS/DPDK has been configured, it may be necessary to add a physical interface to the provider bridge before networking can be fully established if network_interface or network_bond_interfaces have not been defined.

On compute nodes, the following command can be used to attach a NIC port 0000:04:00.0 to the provider bridge br-provider:

ovs-vsctl add-port br-provider 0000:04:00.0 -- set interface 0000:04:00.0 type=dpdk options:dpdk-devargs=0000:04:00.0

Additionally, it may be necessary to make post-installation adjustments to interface queues or other parameters to avoid errors within Open vSwitch:

ovs-vsctl set interface 0000:04:00.0 options:n_txq=5
ovs-vsctl set interface 0000:04:00.0 options:n_rxq=5

The command(s) can be adjusted according to your configuration.


Adding multiple ports to a bridge may result in bridging loops unless bonding is configured.