Make unspecified periodic spaced tasks run on default interval

[OpenStack Infra]

https://review.openstack.org/93767
commit c63fd5a439f22cf32ebea951e6f3b150374004f9
Author: Matt Riedemann <email address hidden>
Date: Thu May 15 07:51:43 2014 -0700

    Make unspecified periodic spaced tasks run on default interval

    When there are multiple tasks with a defined spacing, they can get
    somewhat staggered and force the periodic task processor to run
    additional iterations. Since tasks with no spacing run every time the
    periodic task processor runs, they get run more frequently than one
    would expect.

    Some may argue that this change in behavior could cause some task to
    behave differently than it used to. However, there was never any
    guarantee that the task would run more often than every 60 seconds, and
    in many cases the tasks may already run less frequently than that (due
    to other long-running tasks). So this change should not introduce any
    new issues related to the timing of task execution; it would only serve
    to make the timing more regular.

    We should also make the default interval configurable but that's
    reserved for a separate change.

    DocImpact: periodic tasks without a specific spacing interval will now
    run on the default interval (currently every 60 seconds) rather than
    whenever the task processor runs.

    UpgradeImpact: see above; periodic tasks without a specific spacing
    interval will now run on the default interval which may be less
    often than some tasks run now, but with this change they will run
    on a more consistent interval.

    Closes-Bug: #1319232
    Related-Bug: #1276203
    Related-Bug: #1272830

    Change-Id: I4dd20f68175165d311fa4d3f459c86f2dcac911b

[Lingxian Kong (kong)]

I'm trying, but didn't know which doc to be fixed

[Tom Fifield (fifieldt)]

A welcome change of behaviour, rather than something that needs to be documented