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Re: [Xen-devel] Discussion: Add API to retrieve migration progress

On Fri, 2013-11-08 at 16:10 +0800, Chunyan Liu wrote:
> 2013/11/8 Chunyan Liu <cyliu@xxxxxxxx>
>         Hi, list,
>         One customer requests that we should show migration progress
>         bar in 'xl migrate' or 'virsh migrate', like '-h/--hash'
>         option in 'rpm' command, so that they could see clearly what
>         happened in migration period. To deal with that, we need to
>         have a method to retrieve migration progress. And we hope such
>         stuff could be finally merged to upstream. How do you think?

The current code uses the xtl logging facilities, which IIRC includes
support for progress reporting. xl by default uses the stdio output
implementation provided by the library, which I think logs the progress
as "\rFOO%" but this could be enhanced to use # instead, either by
enhancing the xtl stdio module of by xl providing a customised version
(I think I would prefer the first option). It may also be that the
priority of these messages is not high enough that they are shown by
default. Have you tried "xl -vvv migrate"? Perhaps --hash just needs to
adjust the relevant thresholds.

I'm not sure what meaning %age complete has for a live migration,
doesn't in guest activity make it hard to predict how far through the
process you actually are?

>         Besides, currently, there is some debug messages about the
>         transferred pages and remaining dirty pages in libxc
>         xc_domain_save, but that could not be reported to upper layer.

All this logging should be using the xtl infrastructure and should be
shown if you use verbose logging (e.g. xl -vvv BLAH). If there are
message which aren't using the correct mechanism then please send
patches. Likewise if you think the priority (DEBUG/INFO/WARN etc) given
to particular messages is incorrect please propose patches.

>          We may need a libxl API, which could save the migration
>         status (that could be libxc passed to libxl through pipe or
>         other way); and may need an asyncprogress callback to handle
>         the async thing. Do you have any prefers about how it will be
>         like?

Best to investigate improving the existing logging stuff before going
down this route IMHO.

BTW: there is no need for an IRC ping within an hour of sending the
email. If you don't hear anything for several days (e.g. up to a week)
then maybe it would be appropriate to send a ping, perhaps via email.
Otherwise please just assume that people will read their mail before too


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