Using Open vSwitch with DPDK

This document describes how to use Open vSwitch with DPDK.


Using DPDK with OVS requires configuring OVS at build time to use the DPDK library. The version of DPDK that OVS supports varies from one OVS release to another, as described in the releases FAQ. For build instructions refer to Open vSwitch with DPDK.

Ports and Bridges

ovs-vsctl can be used to set up bridges and other Open vSwitch features. Bridges should be created with a datapath_type=netdev:

$ ovs-vsctl add-br br0 -- set bridge br0 datapath_type=netdev

ovs-vsctl can also be used to add DPDK devices. ovs-vswitchd should print the number of dpdk devices found in the log file:

$ ovs-vsctl add-port br0 dpdk-p0 -- set Interface dpdk-p0 type=dpdk \
$ ovs-vsctl add-port br0 dpdk-p1 -- set Interface dpdk-p1 type=dpdk \

Some NICs (i.e. Mellanox ConnectX-3) have only one PCI address associated with multiple ports. Using a PCI device like above won’t work. Instead, below usage is suggested:

$ ovs-vsctl add-port br0 dpdk-p0 -- set Interface dpdk-p0 type=dpdk \
$ ovs-vsctl add-port br0 dpdk-p1 -- set Interface dpdk-p1 type=dpdk \


Hotplugging physical interfaces is not supported using the above syntax. This is expected to change with the release of DPDK v18.05. For information on hotplugging physical interfaces, you should instead refer to Hotplugging.

After the DPDK ports get added to switch, a polling thread continuously polls DPDK devices and consumes 100% of the core, as can be checked from top and ps commands:

$ top -H
$ ps -eLo pid,psr,comm | grep pmd

Creating bonds of DPDK interfaces is slightly different to creating bonds of system interfaces. For DPDK, the interface type and devargs must be explicitly set. For example:

$ ovs-vsctl add-bond br0 dpdkbond p0 p1 \
    -- set Interface p0 type=dpdk options:dpdk-devargs=0000:01:00.0 \
    -- set Interface p1 type=dpdk options:dpdk-devargs=0000:01:00.1

To stop ovs-vswitchd & delete bridge, run:

$ ovs-appctl -t ovs-vswitchd exit
$ ovs-appctl -t ovsdb-server exit
$ ovs-vsctl del-br br0

OVS with DPDK Inside VMs

Additional configuration is required if you want to run ovs-vswitchd with DPDK backend inside a QEMU virtual machine. ovs-vswitchd creates separate DPDK TX queues for each CPU core available. This operation fails inside QEMU virtual machine because, by default, VirtIO NIC provided to the guest is configured to support only single TX queue and single RX queue. To change this behavior, you need to turn on mq (multiqueue) property of all virtio-net-pci devices emulated by QEMU and used by DPDK. You may do it manually (by changing QEMU command line) or, if you use Libvirt, by adding the following string to <interface> sections of all network devices used by DPDK:

<driver name='vhost' queues='N'/>



determines how many queues can be used by the guest.

This requires QEMU >= 2.2.


Add a userspace bridge and two dpdk (PHY) ports:

# Add userspace bridge
$ ovs-vsctl add-br br0 -- set bridge br0 datapath_type=netdev

# Add two dpdk ports
$ ovs-vsctl add-port br0 phy0 -- set Interface phy0 type=dpdk \
      options:dpdk-devargs=0000:01:00.0 ofport_request=1

$ ovs-vsctl add-port br0 phy1 -- set Interface phy1 type=dpdk
      options:dpdk-devargs=0000:01:00.1 ofport_request=2

Add test flows to forward packets between DPDK port 0 and port 1:

# Clear current flows
$ ovs-ofctl del-flows br0

# Add flows between port 1 (phy0) to port 2 (phy1)
$ ovs-ofctl add-flow br0 in_port=1,action=output:2
$ ovs-ofctl add-flow br0 in_port=2,action=output:1

Transmit traffic into either port. You should see it returned via the other.

PHY-VM-PHY (vHost Loopback)

Add a userspace bridge, two dpdk (PHY) ports, and two dpdkvhostuserclient ports:

# Add userspace bridge
$ ovs-vsctl add-br br0 -- set bridge br0 datapath_type=netdev

# Add two dpdk ports
$ ovs-vsctl add-port br0 phy0 -- set Interface phy0 type=dpdk \
      options:dpdk-devargs=0000:01:00.0 ofport_request=1

$ ovs-vsctl add-port br0 phy1 -- set Interface phy1 type=dpdk
      options:dpdk-devargs=0000:01:00.1 ofport_request=2

# Add two dpdkvhostuserclient ports
$ ovs-vsctl add-port br0 dpdkvhostclient0 \
    -- set Interface dpdkvhostclient0 type=dpdkvhostuserclient \
       options:vhost-server-path=/tmp/dpdkvhostclient0 ofport_request=3
$ ovs-vsctl add-port br0 dpdkvhostclient1 \
    -- set Interface dpdkvhostclient1 type=dpdkvhostuserclient \
       options:vhost-server-path=/tmp/dpdkvhostclient1 ofport_request=4

Add test flows to forward packets between DPDK devices and VM ports:

# Clear current flows
$ ovs-ofctl del-flows br0

# Add flows
$ ovs-ofctl add-flow br0 in_port=1,action=output:3
$ ovs-ofctl add-flow br0 in_port=3,action=output:1
$ ovs-ofctl add-flow br0 in_port=4,action=output:2
$ ovs-ofctl add-flow br0 in_port=2,action=output:4

# Dump flows
$ ovs-ofctl dump-flows br0

Create a VM using the following configuration:




QEMU version



QEMU thread affinity

core 5

taskset 0x20







Qcow2 image






You can do this directly with QEMU via the qemu-system-x86_64 application:

$ export VM_NAME=vhost-vm
$ export GUEST_MEM=3072M
$ export QCOW2_IMAGE=/root/CentOS7_x86_64.qcow2
$ export VHOST_SOCK_DIR=/tmp

$ taskset 0x20 qemu-system-x86_64 -name $VM_NAME -cpu host -enable-kvm \
  -m $GUEST_MEM -drive file=$QCOW2_IMAGE --nographic -snapshot \
  -numa node,memdev=mem -mem-prealloc -smp sockets=1,cores=2 \
  -object memory-backend-file,id=mem,size=$GUEST_MEM,mem-path=/dev/hugepages,share=on \
  -chardev socket,id=char0,path=$VHOST_SOCK_DIR/dpdkvhostclient0,server \
  -netdev type=vhost-user,id=mynet1,chardev=char0,vhostforce \
  -device virtio-net-pci,mac=00:00:00:00:00:01,netdev=mynet1,mrg_rxbuf=off \
  -chardev socket,id=char1,path=$VHOST_SOCK_DIR/dpdkvhostclient1,server \
  -netdev type=vhost-user,id=mynet2,chardev=char1,vhostforce \
  -device virtio-net-pci,mac=00:00:00:00:00:02,netdev=mynet2,mrg_rxbuf=off

For a explanation of this command, along with alternative approaches such as booting the VM via libvirt, refer to DPDK vHost User Ports.

Once the guest is configured and booted, configure DPDK packet forwarding within the guest. To accomplish this, build the testpmd application as described in DPDK in the Guest. Once compiled, run the application:

$ cd $DPDK_DIR/app/test-pmd;
$ ./testpmd -c 0x3 -n 4 --socket-mem 1024 -- \
    --burst=64 -i --txqflags=0xf00 --disable-hw-vlan
$ set fwd mac retry
$ start

When you finish testing, bind the vNICs back to kernel:

$ $DPDK_DIR/usertools/ --bind=virtio-pci 0000:00:03.0
$ $DPDK_DIR/usertools/ --bind=virtio-pci 0000:00:04.0


Valid PCI IDs must be passed in above example. The PCI IDs can be retrieved like so:

$ $DPDK_DIR/usertools/ --status

More information on the dpdkvhostuserclient ports can be found in DPDK vHost User Ports.

PHY-VM-PHY (vHost Loopback) (Kernel Forwarding)

PHY-VM-PHY (vHost Loopback) details steps for PHY-VM-PHY loopback testcase and packet forwarding using DPDK testpmd application in the Guest VM. For users wishing to do packet forwarding using kernel stack below, you need to run the below commands on the guest:

$ ip addr add dev eth1
$ ip addr add dev eth2
$ ip link set eth1 up
$ ip link set eth2 up
$ systemctl stop firewalld.service
$ systemctl stop iptables.service
$ sysctl -w net.ipv4.ip_forward=1
$ sysctl -w net.ipv4.conf.all.rp_filter=0
$ sysctl -w net.ipv4.conf.eth1.rp_filter=0
$ sysctl -w net.ipv4.conf.eth2.rp_filter=0
$ route add -net eth2
$ route add -net eth1
$ arp -s DE:AD:BE:EF:CA:FE
$ arp -s DE:AD:BE:EF:CA:EE

PHY-VM-PHY (vHost Multiqueue)

vHost Multiqueue functionality can also be validated using the PHY-VM-PHY configuration. To begin, follow the steps described in PHY-PHY to create and initialize the database, start ovs-vswitchd and add dpdk-type devices to bridge br0. Once complete, follow the below steps:

  1. Configure PMD and RXQs.

    For example, set the number of dpdk port rx queues to at least 2 The number of rx queues at vhost-user interface gets automatically configured after virtio device connection and doesn’t need manual configuration:

    $ ovs-vsctl set Open_vSwitch . other_config:pmd-cpu-mask=0xc
    $ ovs-vsctl set Interface phy0 options:n_rxq=2
    $ ovs-vsctl set Interface phy1 options:n_rxq=2
  2. Instantiate Guest VM using QEMU cmdline

    We must configure with appropriate software versions to ensure this feature is supported.

    VM Configuration



    QEMU version


    QEMU thread affinity

    2 cores (taskset 0x30)


    4 GB




    Fedora 22



    To do this, instantiate the guest as follows:

    $ export VM_NAME=vhost-vm
    $ export GUEST_MEM=4096M
    $ export QCOW2_IMAGE=/root/Fedora22_x86_64.qcow2
    $ export VHOST_SOCK_DIR=/tmp
    $ taskset 0x30 qemu-system-x86_64 -cpu host -smp 2,cores=2 -m 4096M \
        -drive file=$QCOW2_IMAGE --enable-kvm -name $VM_NAME \
        -nographic -numa node,memdev=mem -mem-prealloc \
        -object memory-backend-file,id=mem,size=$GUEST_MEM,mem-path=/dev/hugepages,share=on \
        -chardev socket,id=char1,path=$VHOST_SOCK_DIR/dpdkvhostclient0,server \
        -netdev type=vhost-user,id=mynet1,chardev=char1,vhostforce,queues=2 \
        -device virtio-net-pci,mac=00:00:00:00:00:01,netdev=mynet1,mq=on,vectors=6 \
        -chardev socket,id=char2,path=$VHOST_SOCK_DIR/dpdkvhostclient1,server \
        -netdev type=vhost-user,id=mynet2,chardev=char2,vhostforce,queues=2 \
        -device virtio-net-pci,mac=00:00:00:00:00:02,netdev=mynet2,mq=on,vectors=6


    Queue value above should match the queues configured in OVS, The vector value should be set to “number of queues x 2 + 2”

  3. Configure the guest interface

    Assuming there are 2 interfaces in the guest named eth0, eth1 check the channel configuration and set the number of combined channels to 2 for virtio devices:

    $ ethtool -l eth0
    $ ethtool -L eth0 combined 2
    $ ethtool -L eth1 combined 2

    More information can be found in vHost walkthrough section.

  4. Configure kernel packet forwarding

    Configure IP and enable interfaces:

    $ ip addr add dev eth0
    $ ip addr add dev eth1
    $ ip link set eth0 up
    $ ip link set eth1 up

    Configure IP forwarding and add route entries:

    $ sysctl -w net.ipv4.ip_forward=1
    $ sysctl -w net.ipv4.conf.all.rp_filter=0
    $ sysctl -w net.ipv4.conf.eth0.rp_filter=0
    $ sysctl -w net.ipv4.conf.eth1.rp_filter=0
    $ ip route add dev eth1
    $ route add default gw eth1
    $ route add default gw eth1
    $ arp -s DE:AD:BE:EF:CA:FE
    $ arp -s DE:AD:BE:EF:CA:FA

    Check traffic on multiple queues:

    $ cat /proc/interrupts | grep virtio

Flow Hardware Offload (Experimental)

The flow hardware offload is disabled by default and can be enabled by:

$ ovs-vsctl set Open_vSwitch . other_config:hw-offload=true

Matches and actions are programmed into HW to achieve full offload of the flow. If not all actions are supported, fallback to partial flow offload (offloading matches only). Moreover, it only works with PMD drivers that support the configured rte_flow actions. Partial flow offload requires support of “MARK + RSS” actions. Full hardware offload requires support of the actions listed below.

The validated NICs are:

  • Mellanox (ConnectX-4, ConnectX-4 Lx, ConnectX-5)

  • Napatech (NT200B01)

Supported protocols for hardware offload matches are:

  • L2: Ethernet, VLAN

  • L3: IPv4, IPv6


Supported actions for hardware offload are:

  • Output.

  • Drop.

  • Modification of Ethernet (mod_dl_src/mod_dl_dst).

  • Modification of IPv4 (mod_nw_src/mod_nw_dst/mod_nw_ttl).

  • Modification of TCP/UDP (mod_tp_src/mod_tp_dst).

  • VLAN Push/Pop (push_vlan/pop_vlan).

  • Modification of IPv6 (set_field:<ADDR>->ipv6_src/ipv6_dst/mod_nw_ttl).

  • Clone/output (tnl_push and output) for encapsulating over a tunnel.

  • Tunnel pop, for packets received on physical ports.


Tunnel offloads are experimental APIs in DPDK. In order to enable it, compile with -DALLOW_EXPERIMENTAL_API.


This DPDK feature is not supported and disabled during OVS initialization.

Further Reading

More detailed information can be found in the DPDK topics section of the documentation. These guides are listed below.