Open vSwitch with DPDK datapath¶

This page serves as a guide for how to use the OVS with DPDK datapath functionality available in the Networking service as of the Mitaka release.

The basics¶

Open vSwitch (OVS) provides support for a Data Plane Development Kit (DPDK) datapath since OVS 2.2, and a DPDK-backed vhost-user virtual interface since OVS 2.4. The DPDK datapath provides lower latency and higher performance than the standard kernel OVS datapath, while DPDK-backed vhost-user interfaces can connect guests to this datapath. For more information on DPDK, refer to the DPDK website.

OVS with DPDK, or OVS-DPDK, can be used to provide high-performance networking between instances on OpenStack compute nodes.

Prerequisites¶

Using DPDK in OVS requires the following minimum software versions:

OVS 2.4
DPDK 2.0
QEMU 2.1.0
libvirt 1.2.13

Multiqueue support is available if the following newer versions are used:

OVS 2.5
DPDK 2.2
QEMU 2.5
libvirt 1.2.17

In both cases, install and configure Open vSwitch with DPDK support for each node. For more information, see the OVS-DPDK installation guide.

Using vhost-user interfaces¶

Once OVS is correctly configured with DPDK support, vhost-user interfaces are completely transparent to the guest. However, guests must request large pages. This can be done through flavors. For example:

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

For more information about the syntax for hw:mem_page_size, refer to the Flavors guide.

Note

vhost-user requires file descriptor-backed shared memory. Currently, the only way to request this is by requesting large pages. This is why instances spawned on hosts with OVS-DPDK must request large pages. The aggregate flavor affinity filter can be used to associate flavors with large page support to hosts with OVS-DPDK support.

Create and add vhost-user network interfaces to instances in the same fashion as conventional interfaces. These interfaces can use the kernel virtio-net driver or a DPDK-compatible driver in the guest

$ openstack server create --nic net-id=$net_id ... testserver

Known limitations¶

This feature is only supported when using the libvirt compute driver, and the KVM/QEMU hypervisor.
Large pages are required for each instance running on hosts with OVS-DPDK. If large pages are not present in the guest, the interface will appear but will not function.
Expect performance degradation of services using tap devices: these devices do not support DPDK. Example services include DVR, FWaaS, or LBaaS.