Using Open vSwitch with DPDK

This document describes how to use Open vSwitch with DPDK datapath.


Using the DPDK datapath requires building OVS with DPDK support. Refer to Open vSwitch with DPDK for more information.

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 \

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

PMD Thread Statistics

To show current stats:

$ ovs-appctl dpif-netdev/pmd-stats-show

To clear previous stats:

$ ovs-appctl dpif-netdev/pmd-stats-clear

Port/RXQ Assigment to PMD Threads

To show port/rxq assignment:

$ ovs-appctl dpif-netdev/pmd-rxq-show

To change default rxq assignment to pmd threads, rxqs may be manually pinned to desired cores using:

$ ovs-vsctl set Interface <iface> \


  • <rxq-affinity-list> is a CSV list of <queue-id>:<core-id> values

For example:

$ ovs-vsctl set interface dpdk-p0 options:n_rxq=4 \

This will ensure:

  • Queue #0 pinned to core 3
  • Queue #1 pinned to core 7
  • Queue #2 not pinned
  • Queue #3 pinned to core 8

After that PMD threads on cores where RX queues was pinned will become isolated. This means that this thread will poll only pinned RX queues.


If there are no non-isolated PMD threads, non-pinned RX queues will not be polled. Also, if provided core_id is not available (ex. this core_id not in pmd-cpu-mask), RX queue will not be polled by any PMD thread.


Assuming you have a vhost-user port transmitting traffic consisting of packets of size 64 bytes, the following command would limit the egress transmission rate of the port to ~1,000,000 packets per second:

$ ovs-vsctl set port vhost-user0 [email protected] -- \
    [email protected] create qos type=egress-policer other-config:cir=46000000 \

To examine the QoS configuration of the port, run:

$ ovs-appctl -t ovs-vswitchd qos/show vhost-user0

To clear the QoS configuration from the port and ovsdb, run:

$ ovs-vsctl destroy QoS vhost-user0 -- clear Port vhost-user0 qos

Refer to vswitch.xml for more details on egress-policer.

Rate Limiting

Here is an example on Ingress Policing usage. Assuming you have a vhost-user port receiving traffic consisting of packets of size 64 bytes, the following command would limit the reception rate of the port to ~1,000,000 packets per second:

$ ovs-vsctl set interface vhost-user0 ingress_policing_rate=368000 \

To examine the ingress policer configuration of the port:

$ ovs-vsctl list interface vhost-user0

To clear the ingress policer configuration from the port:

$ ovs-vsctl set interface vhost-user0 ingress_policing_rate=0

Refer to vswitch.xml for more details on ingress-policer.

Flow Control

Flow control can be enabled only on DPDK physical ports. To enable flow control support at tx side while adding a port, run:

$ ovs-vsctl add-port br0 dpdk-p0 -- set Interface dpdk-p0 type=dpdk \
    options:dpdk-devargs=0000:01:00.0 options:tx-flow-ctrl=true

Similarly, to enable rx flow control, run:

$ ovs-vsctl add-port br0 dpdk-p0 -- set Interface dpdk-p0 type=dpdk \
    options:dpdk-devargs=0000:01:00.0 options:rx-flow-ctrl=true

To enable flow control auto-negotiation, run:

$ ovs-vsctl add-port br0 dpdk-p0 -- set Interface dpdk-p0 type=dpdk \
    options:dpdk-devargs=0000:01:00.0 options:flow-ctrl-autoneg=true

To turn ON the tx flow control at run time for an existing port, run:

$ ovs-vsctl set Interface dpdk-p0 options:tx-flow-ctrl=true

The flow control parameters can be turned off by setting false to the respective parameter. To disable the flow control at tx side, run:

$ ovs-vsctl set Interface dpdk-p0 options:tx-flow-ctrl=false


pdump allows you to listen on DPDK ports and view the traffic that is passing on them. To use this utility, one must have libpcap installed on the system. Furthermore, DPDK must be built with CONFIG_RTE_LIBRTE_PDUMP=y and CONFIG_RTE_LIBRTE_PMD_PCAP=y.


A performance decrease is expected when using a monitoring application like the DPDK pdump app.

To use pdump, simply launch OVS as usual, then navigate to the app/pdump directory in DPDK, make the application and run like so:

$ sudo ./build/app/dpdk-pdump -- \
    --pdump port=0,queue=0,rx-dev=/tmp/pkts.pcap \

The above command captures traffic received on queue 0 of port 0 and stores it in /tmp/pkts.pcap. Other combinations of port numbers, queues numbers and pcap locations are of course also available to use. For example, to capture all packets that traverse port 0 in a single pcap file:

$ sudo ./build/app/dpdk-pdump -- \
    --pdump 'port=0,queue=*,rx-dev=/tmp/pkts.pcap,tx-dev=/tmp/pkts.pcap' \

server-socket-path must be set to the value of ovs_rundir() which typically resolves to /usr/local/var/run/openvswitch.

Many tools are available to view the contents of the pcap file. Once example is tcpdump. Issue the following command to view the contents of pkts.pcap:

$ tcpdump -r pkts.pcap

More information on the pdump app and its usage can be found in the DPDK docs.

Jumbo Frames

By default, DPDK ports are configured with standard Ethernet MTU (1500B). To enable Jumbo Frames support for a DPDK port, change the Interface’s mtu_request attribute to a sufficiently large value. For example, to add a DPDK Phy port with MTU of 9000:

$ ovs-vsctl add-port br0 dpdk-p0 -- set Interface dpdk-p0 type=dpdk \
      options:dpdk-devargs=0000:01:00.0 mtu_request=9000

Similarly, to change the MTU of an existing port to 6200:

$ ovs-vsctl set Interface dpdk-p0 mtu_request=6200

Some additional configuration is needed to take advantage of jumbo frames with vHost ports:

  1. mergeable buffers must be enabled for vHost ports, as demonstrated in the QEMU command line snippet below:

    -netdev type=vhost-user,id=mynet1,chardev=char0,vhostforce \
    -device virtio-net-pci,mac=00:00:00:00:00:01,netdev=mynet1,mrg_rxbuf=on
  2. Where virtio devices are bound to the Linux kernel driver in a guest environment (i.e. interfaces are not bound to an in-guest DPDK driver), the MTU of those logical network interfaces must also be increased to a sufficiently large value. This avoids segmentation of Jumbo Frames received in the guest. Note that ‘MTU’ refers to the length of the IP packet only, and not that of the entire frame.

    To calculate the exact MTU of a standard IPv4 frame, subtract the L2 header and CRC lengths (i.e. 18B) from the max supported frame size. So, to set the MTU for a 9018B Jumbo Frame:

    $ ip link set eth1 mtu 9000

When Jumbo Frames are enabled, the size of a DPDK port’s mbuf segments are increased, such that a full Jumbo Frame of a specific size may be accommodated within a single mbuf segment.

Jumbo frame support has been validated against 9728B frames, which is the largest frame size supported by Fortville NIC using the DPDK i40e driver, but larger frames and other DPDK NIC drivers may be supported. These cases are common for use cases involving East-West traffic only.

Rx Checksum Offload

By default, DPDK physical ports are enabled with Rx checksum offload.

Rx checksum offload can offer performance improvement only for tunneling traffic in OVS-DPDK because the checksum validation of tunnel packets is offloaded to the NIC. Also enabling Rx checksum may slightly reduce the performance of non-tunnel traffic, specifically for smaller size packet.

Extended Statistics

DPDK Extended Statistics API allows PMD to expose unique set of statistics. The Extended statistics are implemented and supported only for DPDK physical and vHost ports.

To enable statistics, you have to enable OpenFlow 1.4 support for OVS. Configure bridge br0 to support OpenFlow version 1.4:

$ ovs-vsctl set bridge br0 datapath_type=netdev \

Check the OVSDB protocols column in the bridge table if OpenFlow 1.4 support is enabled for OVS:

$ ovsdb-client dump Bridge protocols

Query the port statistics by explicitly specifying -O OpenFlow14 option:

$ ovs-ofctl -O OpenFlow14 dump-ports br0

Note: vHost ports supports only partial statistics. RX packet size based counter are only supported and doesn’t include TX packet size counters.

Port Hotplug

OVS supports port hotplugging, allowing the use of ports that were not bound to DPDK when vswitchd was started. In order to attach a port, it has to be bound to DPDK using the script:

$ $DPDK_DIR/tools/ --bind=igb_uio 0000:01:00.0

Then it can be attached to OVS:

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

Detaching will be performed while processing del-port command:

$ ovs-vsctl del-port dpdkx

Sometimes, the del-port command may not detach the device. Detaching can be confirmed by the appearance of an INFO log. For example:

INFO|Device '0000:04:00.1' has been detached

If the log is not seen, then the port can be detached using:

$ ovs-appctl netdev-dpdk/detach 0000:01:00.0

Detaching can be confirmed by console output:

Device '0000:04:00.1' has been detached


Detaching should not be done if a device is known to be non-detachable, as this may cause the device to behave improperly when added back with add-port. The Chelsio Terminator adapters which use the cxgbe driver seem to be an example of this behavior; check the driver documentation if this is suspected.

This feature does not work with some NICs. For more information please refer to the DPDK Port Hotplug Framework.

Vdev Support

DPDK provides drivers for both physical and virtual devices. Physical DPDK devices are added to OVS by specifying a valid PCI address in ‘dpdk-devargs’. Virtual DPDK devices which do not have PCI addresses can be added using a different format for ‘dpdk-devargs’.

Typically, the format expected is ‘eth_<driver_name><x>’ where ‘x’ is a unique identifier of your choice for the given port.

For example to add a dpdk port that uses the ‘null’ DPDK PMD driver:

$ ovs-vsctl add-port br0 null0 -- set Interface null0 type=dpdk \

Similarly, to add a dpdk port that uses the ‘af_packet’ DPDK PMD driver:

$ ovs-vsctl add-port br0 myeth0 -- set Interface myeth0 type=dpdk \

More information on the different types of virtual DPDK PMDs can be found in the DPDK documentation.

Note: Not all DPDK virtual PMD drivers have been tested and verified to work.

EMC Insertion Probability

By default 1 in every 100 flows are inserted into the Exact Match Cache (EMC). It is possible to change this insertion probability by setting the emc-insert-inv-prob option:

$ ovs-vsctl --no-wait set Open_vSwitch . other_config:emc-insert-inv-prob=N


is a positive integer representing the inverse probability of insertion ie. on average 1 in every N packets with a unique flow will generate an EMC insertion.

If N is set to 1, an insertion will be performed for every flow. If set to 0, no insertions will be performed and the EMC will effectively be disabled.

With default N set to 100, higher megaflow hits will occur initially as observed with pmd stats:

$ ovs-appctl dpif-netdev/pmd-stats-show

For certain traffic profiles with many parallel flows, it’s recommended to set N to ‘0’ to achieve higher forwarding performance.

For more information on the EMC refer to Open vSwitch with DPDK .

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 betwen 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 dpdkvhostuser 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 dpdkvhostuser ports
$ ovs-vsctl add-port br0 dpdkvhostuser0 \
    -- set Interface dpdkvhostuser0 type=dpdkvhostuser ofport_request=3
$ ovs-vsctl add-port br0 dpdkvhostuser1 \
    -- set Interface dpdkvhostuser1 type=dpdkvhostuser ofport_request=4

Add test flows to forward packets betwen 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:

configuration values comments
qemu version qemu thread affinity memory cores Qcow2 image mrg_rxbuf 2.2.0 core 5 4GB 2 CentOS7 off n/a taskset 0x20 n/a n/a n/a n/a

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=/usr/local/var/run/openvswitch

$ 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/dpdkvhostuser0 \
  -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/dpdkvhostuser1 \
  -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 dpdkvhostuser 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.

    Recommended BIOS Settings
    Setting Value
    QEMU version 2.5.0
    QEMU thread affinity 2 cores (taskset 0x30)
    Memory 4 GB
    Cores 2
    Distro Fedora 22
    Multiqueue Enabled

    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=/usr/local/var/run/openvswitch
    $ 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=$VHOST_SOCK_DIR/dpdkvhostuser0 \
        -netdev type=vhost-user,id=mynet1,chardev=char1,vhostforce,queues=2 \
        -device virtio-net-pci,mac=00:00:00:00:00:01,netdev=mynet1,mq=on,vectors=6 \
        -chardev socket,id=char2,path=$VHOST_SOCK_DIR/dpdkvhostuser1 \
        -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