[OVN] Documentation: SR-IOV guide for OVN
This patch is adding some documentation about OVN + SR-IOV. Change-Id: I0353c24d1ff795ad09a9cdad28b6a839e916644c Signed-off-by: Lucas Alvares Gomes <lucasagomes@gmail.com>
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Lucas Alvares Gomes
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@ -13,3 +13,4 @@ OVN Driver Administration Guide
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refarch/refarch
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dpdk
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troubleshooting
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sriov
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171
doc/source/admin/ovn/sriov.rst
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171
doc/source/admin/ovn/sriov.rst
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.. _ovn_sriov:
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====================
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SR-IOV guide for OVN
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====================
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The purpose of this page is to describe how SR-IOV works with OVN. Prior
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to reading this document, it is recommended to first read :ref:`the
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basic guide for SR-IOV<config-sriov>`.
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External ports
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~~~~~~~~~~~~~~
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In order for SR-IOV to work with the
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Neutron driver we are leveraging the `external ports
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<https://github.com/ovn-org/ovn/commit/96080083581275afaec8bc281d6a648aff7ef39e>`_
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feature from the OVN project. When virtual machines are booted
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on hypervisors supporting SR-IOV nics, the local ovn-controllers are
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unable to reply to the VM's DHCP, internal DNS, IPv6 router solicitation
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requests, etc... since the hypervisor is bypassed in the SR-IOV case. OVN
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then introduced the idea of having ``external`` ports which are able to
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reply on behalf of those VM ports external to the hypervisor that they
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are running on.
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The OVN Neutron driver will create a port of the type ``external``
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for ports with the following VNICs set:
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* direct
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* direct-physical
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* macvtap
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Also, ports of the type ``external`` will be scheduled on the gateway
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nodes (controller or networker nodes) in HA mode by the OVN Neutron
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driver. Check the `OVN Database information`_ section for more
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information.
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Environment setup for OVN SR-IOV
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~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
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There are a very few differences between setting up an environment for
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SR-IOV for the OVS and OVN Neutron drivers. As mentioned at the beginning
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of this document, the instructions from the :ref:`the basic guide for
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SR-IOV<config-sriov>` are required for getting SR-IOV working with the
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OVN driver.
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The only differences required for an OVN deployment are:
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* When configuring the ``mechanism_drivers`` in the *ml2_conf.ini* file
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we should specify ``ovn`` driver instead of the ``openvswitch`` driver
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* Disabling the Neutron DHCP agent
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* Deploying the OVN Metadata agent on the gateway nodes (controller
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or networker nodes)
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OVN Database information
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~~~~~~~~~~~~~~~~~~~~~~~~
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Before getting into the ports information, the previous sections
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talks about **gateway nodes**, the OVN Neutron driver identifies
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a gateway node by the ``ovn-cms-options=enable-chassis-as-gw`` and
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``ovn-bridge-mappings`` options in the external_ids column from the
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``Chassis`` table in the OVN Southbound database:
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.. code-block:: bash
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$ ovn-sbctl list Chassis
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_uuid : 12b13aff-a821-4cde-a4ac-d9cf8e2c91bc
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external_ids : {ovn-cms-options=enable-chassis-as-gw, ovn-bridge-mappings="public:br-ex", ...}
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hostname : controller-0
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name : "1a462946-ccfd-46a6-8abf-9dca9eb558fb"
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...
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.. end
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For more information about both of these options, please
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take a look at the `ovn-controller documentation
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<http://www.openvswitch.org/support/dist-docs/ovn-controller.8.html>`_.
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These options can be set by running the following command locally on each
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gateway node (note, the ``ovn-bridge-mappings`` will need to be adapted
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to your environment):
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.. code-block:: bash
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$ ovs-vsctl set Open_vSwitch . external-ids:ovn-cms-options=\"enable-chassis-as-gw\" external-ids:ovn-bridge-mappings=\"public:br-ex\"
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.. end
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As mentioned in the `External ports`_ section, every time a Neutron port
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with a certain VNIC is created the OVN driver will create a port of the
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type ``external`` in the OVN Northbound database. These ports can be
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found by issuing the following command:
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.. code-block:: bash
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$ ovn-nbctl find Logical_Switch_Port type=external
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_uuid : 105e83ae-252d-401b-a1a7-8d28ec28a359
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ha_chassis_group : [43047e7b-4c78-4984-9788-6263fcc69885]
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type : external
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...
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.. end
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The ``ha_chassis_group`` column indicates which HA Chassis Group that
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port belongs to, to find that group do:
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.. code-block:: bash
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# The UUID is the one from the ha_chassis_group column from
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# the Logical_Switch_Port table
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$ ovn-nbctl list HA_Chassis_Group 43047e7b-4c78-4984-9788-6263fcc69885
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_uuid : 43047e7b-4c78-4984-9788-6263fcc69885
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external_ids : {}
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ha_chassis : [3005bf84-fc95-4361-866d-bfa1c980adc8, 72c7671e-dd48-4100-9741-c47221672961]
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name : default_ha_chassis_group
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.. end
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.. note::
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For now, the OVN driver only has one HA Chassis Group created called
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``default_ha_chassis_group``. All ``external`` ports in the system
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will belong to this group.
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The chassis that are members of the ``default_ha_chassis_group`` HA
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Chassis Group are listed in the ``ha_chassis`` column. Those are the
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gateway nodes (controller or networker nodes) in the deployment and
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it's where the ``external`` ports will be scheduled. In order to
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find which gateway node the external ports are scheduled on use the
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following command:
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.. code-block:: bash
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# The UUIDs are the UUID members of the HA Chassis Group
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# (ha_chassis column from the HA_Chassis_Group table)
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$ ovn-nbctl list HA_Chassis 3005bf84-fc95-4361-866d-bfa1c980adc8 72c7671e-dd48-4100-9741-c47221672961
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_uuid : 3005bf84-fc95-4361-866d-bfa1c980adc8
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chassis_name : "1a462946-ccfd-46a6-8abf-9dca9eb558fb"
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external_ids : {}
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priority : 32767
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_uuid : 72c7671e-dd48-4100-9741-c47221672961
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chassis_name : "a0cb9d55-a6da-4f84-857f-d4b674088c8c"
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external_ids : {}
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priority : 32766
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.. end
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Note the ``priority`` column from the previous command, the chassis with
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the highest ``priority`` from that list is the chassis that will have
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the external ports scheduled on it. In our example above, the chassis
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with the UUID ``1a462946-ccfd-46a6-8abf-9dca9eb558fb`` is the one.
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Whenever the chassis with the highest priority goes down, the ports will
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be automatically scheduled on the next chassis with the highest priority
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which is alive. So, the external ports are HA out of the box.
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Known limitations
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~~~~~~~~~~~~~~~~~
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The current SR-IOV implementation for the OVN Neutron driver has a few
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known limitations that should be addressed in the future:
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#. At the moment, **all** external ports will be scheduled on a single
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gateway node since there's only one HA Chassis Group for all of those
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ports.
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#. Routing on VLAN tenant network will not work with SR-IOV. This
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is because the external ports are not being co-located with
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the logical router's gateway ports, for more information take a look at
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`bug #1875852 <https://bugs.launchpad.net/neutron/+bug/1875852>`_.
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