Merge "Update live_migration_downtime definition"

Author: Zuul

doc/source/admin/configuring-migrations.rst

@@ -263,8 +263,10 @@ memory-intensive instances succeed.
       live_migration_downtime_steps = 10
       live_migration_downtime_delay = 75
 
-   ``live_migration_downtime`` sets the maximum permitted downtime for a live
-   migration, in *milliseconds*.  The default is 500.
+   ``live_migration_downtime`` sets the target maximum period of time Nova will
+   try to keep the instance paused during the last part of the memory copy, in
+   *milliseconds*. This value may be exceeded if there is any reduction on the
+   transfer rate after the VM is paused. The default is 500.
 
    ``live_migration_downtime_steps`` sets the total number of adjustment steps
    until ``live_migration_downtime`` is reached.  The default is 10 steps.

nova/conf/libvirt.py

@@ -321,13 +321,14 @@
                default=500,
                min=100,
                help="""
-Maximum permitted downtime, in milliseconds, for live migration
-switchover.
+Target maximum period of time Nova will try to keep the instance paused
+during the last part of the memory copy, in *milliseconds*.
 
 Will be rounded up to a minimum of 100ms. You can increase this value
 if you want to allow live-migrations to complete faster, or avoid
 live-migration timeout errors by allowing the guest to be paused for
-longer during the live-migration switch over.
+longer during the live-migration switch over. This value may be exceeded
+if there is any reduction on the transfer rate after the VM is paused.
 
 Related options: