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Excerpts from Markus Zoeller's message of 2016-03-03 12:50:55 +0100:
> Doug Hellmann <doug at doughellmann.com> wrote on 03/02/2016 07:19:22 PM:
> 
> > From: Doug Hellmann <doug at doughellmann.com>
> > To: openstack-dev <openstack-dev at lists.openstack.org>
> > Date: 03/02/2016 07:20 PM
> > Subject: Re: [openstack-dev] [nova] config options help text 
> > improvement: current status
> > 
> > Excerpts from Markus Zoeller's message of 2016-03-02 18:45:45 +0100:
> > 
> > [a lot snipped]
> > 
> > > Appendix
> > > ========
> > > 
> > > Example of the help text improvement
> > > -----------------------------------
> > > As an example, compare the previous documentation of the scheduler 
> > > option "scheduler_tracks_instance_changes". 
> > > Before we started:
> > > 
> > >     # Determines if the Scheduler tracks changes to instances to help 
> > >     # with its filtering decisions. (boolean value)
> > >     #scheduler_tracks_instance_changes = true
> > > 
> > > After the improvement:
> > > 
> > >     # The scheduler may need information about the instances on a host 
> 
> > >     # in order to evaluate its filters and weighers. The most common 
> > >     # need for this information is for the (anti-)affinity filters, 
> > >     # which need to choose a host based on the instances already 
> running
> > >     # on a host.
> > >     #
> > >     # If the configured filters and weighers do not need this 
> information,
> > >     # disabling this option will improve performance. It may also be 
> > >     # disabled when the tracking overhead proves too heavy, although 
> > >     # this will cause classes requiring host usage data to query the 
> > >     # database on each request instead.
> > >     #
> > >     # This option is only used by the FilterScheduler and its 
> subclasses;
> > >     # if you use a different scheduler, this option has no effect.
> > >     #
> > >     # * Services that use this:
> > >     #
> > >     #     ``nova-scheduler``
> > >     #
> > >     # * Related options:
> > >     #
> > >     #     None
> > >     #  (boolean value)
> > >     #scheduler_tracks_instance_changes = true
> > 
> > If, in the course of adding this information, you think it would be
> > useful for oslo.config or the config generator to provide a way to
> > expose or derive the information, let me know. We're going to be doing
> > some more work on the config generator to enable some automation in the
> > config reference guide maintained by the docs team, and this looks like
> > the sort of thing that might be useful to include in a discoverable way
> > (not just within the comment text for the options).
> > 
> > Doug
> 
> I assume you mean the information about the services which use the
> config option. We have indeed the concern that this is prone to be
> outdated easily. I was thinking if it would make sense to do an
> analysis of the module imports based on the nova services starter
> scripts [1] to derive that information but I couldn't dive into that.
> Long story short, if the config generator could derive that, that
> would be awesome.

The config generator can't derive it directly, but we could make it
smart enough to know that if it is given multiple input files it should
list all of the input files that result in a given input option being
loaded, and map that to a service name somehow. You still have to do the
analysis by hand and set up the different input files, though.

Doug

> 
> References:
> [1] https://git.openstack.org/cgit/openstack/nova/tree/nova/cmd
> 
> Regards, Markus Zoeller (markus_z)
>