Spec: Add port hints and hint ovs-tx-steering
Change-Id: Ia2bd912e65d5091ca17f26b6cc4b4be3fc981324 Related-Bug: #1990842
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Bence Romsics
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This work is licensed under a Creative Commons Attribution 3.0 Unported
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License.
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http://creativecommons.org/licenses/by/3.0/legalcode
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==========================================================
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Expose backend hints in the port API, hint ovs-tx-steering
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==========================================================
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RFE: https://bugs.launchpad.net/neutron/+bug/1990842
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Introduce a port attribute that allows passing in backend specific hints
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mainly to allow backend specific performance tuning.
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Problem Description
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===================
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Some of our performance sensitive users would like to tweak Open vSwitch's Tx
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packet steering option [1]_ under OpenStack.
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This is available since Open vSwitch v2.17.0. [2]_, [3]_
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Proposed Change
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===============
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We propose to introduce two new extension: ``port-hints`` and
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``port-hint-ovs-tx-steering``.
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The purpose of decomposing this feature to two extensions is
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extensibility: to allow other hints in the future. ``port-hints``
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signals the presence of a new port attribute, for details see
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below. ``port-hint-foobar`` signals what values of the new port attribute
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(or which is the same: what hints) are known to a Neutron instance.
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``port-hints`` adds a new port attribute: ``hints``. Its default
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policy is ``admin_only``. Its value is a dict (by default empty).
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The dict is keyed by the standard mechanism driver aliases as in [4]_.
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This spec allows only a single key: ``openvswitch``. Other keys for
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other mechanism drivers may be introduced by later specs. The value
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for a mechanism_driver is possibly a complex structure, but at least
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a dict on the top level. In this spec we only partially define its
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format - introducing one hint. This is marked by the second extension
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``port-hint-ovs-tx-steering``. Definition of other hints is left to
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future specs. Here consider this partial body for a create port request:
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::
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{
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"port": {
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"hints": {
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"openvswitch": {"other_config": {"tx-steering": "thread"|"hash"}}}
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...
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}
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Everything in ``hints`` is interpreted not as a demand, but as a
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suggestion. That is, neutron is free to ignore some or all of the
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requested hints without returning an error response or putting the
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port into an error status. Particularly neutron is free to ignore the
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requested hints when the port is bound by a different mechanism driver.
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``hints`` can be set at port create or update, but there's no guarantee
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that an update to the hints after the port was bound will have any effect.
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``hints`` is intentionally not named ``binding:hints`` and it should
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not be affecting the binding process and decision.
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In the ``openstack`` CLI we propose to expose the above API feature as:
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::
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openstack port create/set --hint HINT-ALIAS[:HINT-VALUE] [--hint ...] ...
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For example:
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::
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openstack port create --hint ovs-tx-steering:thread ...
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openstack port create --hint ovs-tx-steering:hash ...
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The above CLI syntax allows boolean and key:value type hints. There is
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an arbitrary but documented mapping between a HINT-ALIAS and the full
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fledged data structure passed in the API.
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Alternatively we could pass in a sizable JSON blob, but I believe that
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would lead to a cumbersome CLI experience.
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Given the ovs-tx-steering hint passed in, ovs-agent can set the
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corresponding OVS interface's other_config (using the python native
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interface of course, not ovs-vsctl):
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::
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sudo ovs-vsctl set Interface ovs-interface-of-the-port other_config:tx-steering=thread
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sudo ovs-vsctl set Interface ovs-interface-of-the-port other_config:tx-steering=hash
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The default value of hint ``ovs-tx-steering`` is ``thread``.
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API Impact
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----------
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Add a new admin_only field to the port resource called ``hints``. This
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field can be present in GET, POST and PUT requests. For its semantics
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please see above.
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DB Impact
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---------
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Extend the ``ports`` table with column ``hints``.
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Client Impact
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-------------
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Relevant changes in osc and openstacksdk.
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Testing
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-------
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* Unit tests.
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* Tempest tests in neutron-tempest-plugin.
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Assignee(s)
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-----------
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* Bence Romsics <bence.romsics@gmail.com>
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References
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==========
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.. [1] https://docs.openvswitch.org/en/latest/topics/userspace-tx-steering/
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.. [2] https://github.com/openvswitch/ovs/blob/7af5c33c1629b309cbcbe3b6c9c3bd6d3b4c0abf/NEWS#L103
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.. [3] https://github.com/openvswitch/ovs/commit/c18e707b2f259438633af5b23df53e1409472871
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.. [4] https://opendev.org/openstack/neutron/src/commit/31af8d1539c9c88be12c37120a6d43df528349bd/setup.cfg#L98-L112
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