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Reviewed:  https://review.openstack.org/556332
Committed: https://git.openstack.org/cgit/openstack/nova/commit/?id=8d68f2323040908008fcd023a40f7fadf5641e59
Submitter: Zuul
Branch:    master

commit 8d68f2323040908008fcd023a40f7fadf5641e59
Author: Matt Riedemann <mriedem.os@xxxxxxxxx>
Date:   Sun Mar 25 16:56:19 2018 -0400

    Avoid unnecessary port update during live migration
    
    The ComputeManager.pre_live_migration method, which runs on the
    destination host during live migration, calls setup_networks_on_host
    with the destination host which causes the "migrating_to" attribute
    to get set to the destination host in the port binding profile. This
    is to initiate setting up floating IP information on the destination
    host for DVR.
    
    The ComputeManager.post_live_migration_at_destination method calls the
    same method from the destination host, so at this point the "migrating_to"
    attribute is already set to the destination host in the port binding
    profile from pre_live_migration and we make unnecessary port update calls
    to Neutron for each port attached to the instance.
    
    This change simply checks to see if the "migrating_to" attribute is
    already set to the given host and if so, skips the port update call.
    
    Change-Id: I8b2ffd94c5ff0881d0df4efdde9be938888c16d7
    Closes-Bug: #1758453


** Changed in: nova
       Status: In Progress => Fix Released

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https://bugs.launchpad.net/bugs/1758453

Title:
  Port binding 'migrating_to' attribute needlessly updated in post-live-
  migration for neutron

Status in OpenStack Compute (nova):
  Fix Released

Bug description:
  During live migration, the setup_networks_on_host neutronv2 API method
  checks to see if the provided host is different from the existing
  instance.host and if so, it knows the instance is being migrated and
  sets the 'migrating_to' attribute to the new host in the ports binding
  profile:

  https://github.com/openstack/nova/blob/55b22a54e65728712670c5dde5a833f5349e5b2f/nova/network/neutronv2/api.py#L351

  https://github.com/openstack/nova/blob/55b22a54e65728712670c5dde5a833f5349e5b2f/nova/network/neutronv2/api.py#L322

  And then updates the port.

  That happens in pre_live_migration which runs on the dest host:

  https://github.com/openstack/nova/blob/55b22a54e65728712670c5dde5a833f5349e5b2f/nova/compute/manager.py#L6007

  And it also happens again in post_live_migration_at_destination which
  runs on the destination host:

  https://github.com/openstack/nova/blob/55b22a54e65728712670c5dde5a833f5349e5b2f/nova/compute/manager.py#L6382

  Since the neutronv2 API code doesn't check to see if the
  'migrating_to' attribute is already set:

  https://github.com/openstack/nova/blob/55b22a54e65728712670c5dde5a833f5349e5b2f/nova/network/neutronv2/api.py#L322

  It does a redundant PUT (port update) for no actual change.

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