libvirt: support management of downtime during migration

[OpenStack Infra]

https://review.openstack.org/162253
commit 07c7e5caf2819d96809af1b9a19c046b9fd09851
Author: Daniel P. Berrange <email address hidden>
Date: Fri Mar 6 16:12:28 2015 +0000

    libvirt: support management of downtime during migration

    Currently live migration runs with the default maximum downtime
    setting defined by QEMU. This is often inadequate to allow
    migration of large VMs to ever complete. Rather than trying to
    invent a new policy for changing downtime in OpenStack, copy
    the existing logic that is successfully battle tested by the
    oVirt project in VDSM.

    Note that setting the downtime step delay based on guest RAM size
    is an inexact science, as RAM size is only one factor influencing
    success of migration. Just as important is the rate of dirtying
    data in the guest, but this is based on guest workload which is
    not something Nova has visibility into. The bottleneck is the
    network which needs to be able to keep up with the dirtying of
    data in the guest. The greater the overall RAM size, the more
    time is required to transfer the total guest memory. So for
    larger guest sizes, we need to allow greater time for the guest
    to attempt to successfully migrate before increasing the max
    downtime. Scaling downtime step delay according to the overall
    guest RAM size is a reasonable, albeit not foolproof, way to
    tune migration to increase chances of success.

    This adds three host level config parameters which admins can
    use to control the base downtime value and the rate at which
    downtime is allowed to be increased during migration.

    Related-bug: #1429220
    DocImpact: three new libvirt configuration parameters in
               nova.conf allow the administrator to control
               the maximum permitted downtime for migration
               making migration more likely to complete for
               large VMs.
    Change-Id: I1992ffe9d3b2ff8d436cf1c419af9a238a8fecd8

[Gauvain Pocentek (gpocentek)]

Related to bug #1483568 if I understand correctly.

[OpenStack Infra (hudson-openstack)]

Fix proposed to branch: master
Review: https://review.openstack.org/219959

[OpenStack Infra (hudson-openstack)]

Fix proposed to branch: master
Review: https://review.openstack.org/220869

[OpenStack Infra (hudson-openstack)]

Reviewed: https://review.openstack.org/219959
Committed: https://git.openstack.org/cgit/openstack/openstack-manuals/commit/?id=dfeb6578b6448353ea2e62163626eae310d00ac5
Submitter: Jenkins
Branch: master

commit dfeb6578b6448353ea2e62163626eae310d00ac5
Author: Lana Brindley <email address hidden>
Date: Thu Sep 3 12:09:37 2015 +1000

    Added extra libvirt live migration config parameters

    Three live migration config params were added to nova.conf to manage downtime
    while performing live migrations. This patch adds these to the libvirt
    live migration section. Another patch forthcoming to include more conceptual
    information about this topic elsewhere in the book.

    Change-Id: I99db413e321aaef092bbe10cb59b6084909f0c1c
    Partial-Bug: 1483566
    Partial-Bug: 1483568

[OpenStack Infra (hudson-openstack)]

Reviewed: https://review.openstack.org/220869
Committed: https://git.openstack.org/cgit/openstack/openstack-manuals/commit/?id=3d7b8f4171b3b5d1b5295a619598e7498ac54ddd
Submitter: Jenkins
Branch: master

commit 3d7b8f4171b3b5d1b5295a619598e7498ac54ddd
Author: Lana Brindley <email address hidden>
Date: Mon Sep 7 12:22:45 2015 +1000

    Add more concept info about live migration downtime calculation

    Adds conceptual information around the downtime config parameters. The
    parameters themselves have already been added in a previous patch.

    Change-Id: I55c3da9892e396d1e6e90450ec9b9c6ce7d6b9f9
    Closes-Bug: 1483566
    Closes-Bug: 1483568

[OpenStack Infra (hudson-openstack)]

This issue was fixed in the openstack/openstack-manuals 15.0.0 release.