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.. _config-ovs-dpdk:
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===============================
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Open vSwitch with DPDK Datapath
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===============================
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This page serves as a guide for how to use the OVS with DPDK datapath
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functionality available in the Networking service as of the Mitaka release.
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The basics
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~~~~~~~~~~
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Open vSwitch (OVS) provides support for a Data Plane Development Kit (DPDK)
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datapath since OVS 2.2, and a DPDK-backed ``vhost-user`` virtual interface
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since OVS 2.4. The DPDK datapath provides lower latency and higher performance
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than the standard kernel OVS datapath, while DPDK-backed ``vhost-user``
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interfaces can connect guests to this datapath. For more information on DPDK,
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refer to the `DPDK <http://dpdk.org/>`__ website.
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OVS with DPDK, or OVS-DPDK, can be used to provide high-performance networking
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between instances on OpenStack compute nodes.
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Prerequisites
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-------------
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Using DPDK in OVS requires the following minimum software versions:
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* OVS 2.4
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* DPDK 2.0
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* QEMU 2.1.0
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* libvirt 1.2.13
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Support of ``vhost-user`` multiqueue that enables use of multiqueue with
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``virtio-net`` and ``igb_uio`` is available if the following newer
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versions are used:
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* OVS 2.5
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* DPDK 2.2
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* QEMU 2.5
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* libvirt 1.2.17
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In both cases, install and configure Open vSwitch with DPDK support for each
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node. For more information, see the
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`OVS-DPDK <https://github.com/openvswitch/ovs/blob/master/Documentation/intro/install/dpdk.rst>`__
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installation guide (select an appropriate OVS version in the
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:guilabel:`Branch` drop-down menu).
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:doc:`/contributor/internals/ovs_vhostuser`
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for configuration of neutron OVS agent.
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In case you wish to configure multiqueue, see the
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`OVS configuration chapter on vhost-user
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<http://wiki.qemu.org/Documentation/vhost-user-ovs-dpdk#Enabling_multi-queue>`__
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in QEMU documentation.
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The technical background of multiqueue is explained in the corresponding
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`blueprint <https://specs.openstack.org/openstack/nova-specs/specs/liberty/implemented/libvirt-virtiomq.html>`__.
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Additionally, OpenStack supports ``vhost-user`` reconnect feature starting
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from the Ocata release, as implementation of fix for
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`bug 1604924 <https://bugs.launchpad.net/neutron/+bug/1604924>`__.
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Starting from OpenStack Ocata release this feature is used without any
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configuration necessary in case the following minimum software versions
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are used:
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* OVS 2.6
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* DPDK 16.07
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* QEMU 2.7
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The support of this feature is not yet present in ML2 OVN and ODL
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mechanism drivers.
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Using vhost-user interfaces
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~~~~~~~~~~~~~~~~~~~~~~~~~~~
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Once OVS and neutron are correctly configured with DPDK support,
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``vhost-user`` interfaces are completely transparent to the guest
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(except in case of multiqueue configuration described below).
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However, guests must request huge pages. This can be done through flavors.
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For example:
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.. code-block:: console
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$ openstack flavor set m1.large --property hw:mem_page_size=large
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For more information about the syntax for ``hw:mem_page_size``, refer to the
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`Flavors <https://docs.openstack.org/nova/latest/admin/flavors.html>`__ guide.
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.. note::
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``vhost-user`` requires file descriptor-backed shared memory. Currently, the
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only way to request this is by requesting large pages. This is why instances
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spawned on hosts with OVS-DPDK must request large pages. The aggregate
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flavor affinity filter can be used to associate flavors with large page
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support to hosts with OVS-DPDK support.
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Create and add ``vhost-user`` network interfaces to instances in the same
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fashion as conventional interfaces. These interfaces can use the kernel
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``virtio-net`` driver or a DPDK-compatible driver in the guest
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.. code-block:: console
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$ openstack server create --nic net-id=$net_id ... testserver
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Using vhost-user multiqueue
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~~~~~~~~~~~~~~~~~~~~~~~~~~~
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To use this feature, the following should be set in the flavor extra specs
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(flavor keys):
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.. code-block:: console
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$ openstack flavor set $m1.large --property hw:vif_multiqueue_enabled=true
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This setting can be overridden by the image metadata property if the feature
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is enabled in the extra specs:
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.. code-block:: console
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$ openstack image set --property hw_vif_multiqueue_enabled=true IMAGE_NAME
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Support of ``virtio-net`` multiqueue needs to be present in kernel of
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guest VM and is available starting from Linux kernel 3.8.
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Check pre-set maximum for number of combined channels in channel
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configuration.
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Configuration of OVS and flavor done successfully should result in
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maximum being more than '1'):
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.. code-block:: console
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$ ethtool -l INTERFACE_NAME
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To increase number of current combined channels run following command in
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guest VM:
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.. code-block:: console
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$ ethtool -L INTERFACE_NAME combined QUEUES_NR
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The number of queues should typically match the number of vCPUs
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defined for the instance. In newer kernel versions
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this is configured automatically.
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Known limitations
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~~~~~~~~~~~~~~~~~
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* This feature is only supported when using the libvirt compute driver, and the
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KVM/QEMU hypervisor.
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* Huge pages are required for each instance running on hosts with OVS-DPDK.
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If huge pages are not present in the guest, the interface will appear but
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will not function.
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* Expect performance degradation of services using tap devices: these devices
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do not support DPDK. Example services include DVR and FWaaS.
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* When the ``ovs_use_veth`` option is set to ``True``, any traffic sent
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from a DHCP namespace will have an incorrect TCP checksum.
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This means that if ``enable_isolated_metadata`` is set to ``True`` and
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metadata service is reachable through the DHCP namespace, responses from
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metadata will be dropped due to an invalid checksum. In such cases,
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``ovs_use_veth`` should be switched to ``False`` and Open vSwitch (OVS)
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internal ports should be used instead.
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