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Subject: Re: [OMPI devel] XML request
From: Greg Watson (g.watson_at_[hidden])
Date: 2009-08-31 21:26:20

Hey Ralph,

Unfortunately I don't think this is going to work for us. Most of the
time we're starting the mpirun command using the ssh exec or shell
service, neither of which provide any mechanism for reading from file
descriptors other than 1 or 2. The only alternatives I see are:

1. Provide a separate command that starts mpirun at the end of a pipe
that is connected to the fd passed using the -xml-fd argument. This
command would need to be part of the OMPI distribution, because the
whole purpose of the XML was to provide an out-of-the-box experience
when using PTP with OMPI.

2. Implement an -xml-file option, but I could write the code for you.

3. Go back to limiting XML output to the map only.

None of these are particularly ideal. If you can think of anything
else, let me know.


On Aug 30, 2009, at 10:36 AM, Ralph Castain wrote:

> What if we instead offered a -xml-fd N option? I would rather not
> create a file myself. However, since you are calling mpirun
> yourself, this would allow you to create a pipe on your end, and
> then pass us the write end of the pipe. We would then send all XML
> output down that pipe.
> Jeff and I chatted about this and felt this might represent the
> cleanest solution. Sound okay?
> On Aug 28, 2009, at 6:33 AM, Greg Watson wrote:
>> Ralph,
>> Would this be doable? If we could guarantee that the only output
>> that went to the file was XML then that would solve the problem.
>> Greg
>> On Aug 28, 2009, at 5:39 AM, Ashley Pittman wrote:
>>> On Thu, 2009-08-27 at 23:46 -0400, Greg Watson wrote:
>>>> I didn't realize it would be such a problem. Unfortunately there is
>>>> simply no way to reliably parse this kind of output, because it is
>>>> impossible to know what the error messages are going to be, and
>>>> presumably they could include XML-like formatting as well. The
>>>> whole
>>>> point of the XML was to try and simplify the parsing of the mpirun
>>>> output, but it now looks like it's actually more difficult.
>>> I thought this might be difficult when I saw you were attempting it.
>>> Let me tell you about what Valgrind does because they have similar
>>> problems. Initially they just had added --xml=yes option which
>>> put most
>>> of the valgrind (as distinct from application) output in xml
>>> tags. This
>>> works for simple cases and if you mix it with --log-
>>> file=<filename> it
>>> keeps the valgrind output separate from the application output.
>>> Unfortunately there are lots of places throughout the code where
>>> developers have inserted print statements (in the valgrind case
>>> these
>>> all go to the logfile) which means the xml is interspersed with
>>> non-xml
>>> output and hence impossibly to parse reliably.
>>> What they have now done in the current release is to add a extra
>>> --xml-file=<file> option as well as the --log-file=<file> option.
>>> Now
>>> in the simple case all output from a normal run goes well
>>> formatted to
>>> the xml file and the log file remains empty, any tool that wraps
>>> around
>>> valgrind can parse the xml which is guaranteed to be well
>>> formatted and
>>> it can detect the presence of other messages by looking for output
>>> in
>>> the standard log file. The onus is then on tool writers to look
>>> at the
>>> remaining cases and decide if they are common or important enough to
>>> wrap in xml and propose a patch or removal of the non-formatted
>>> message
>>> entirely.
>>> The above seems to work well, having a separate log file for xml
>>> is a
>>> huge step forward as it means whilst the xml isn't necessarily
>>> complete
>>> you can both parse it and are able to tell when it's missing
>>> something.
>>> Of course when looking at this level of tool integration it's
>>> better to
>>> use sockets that files (e.g. --xml-socket=localhost:1234 rather than
>>> --xml-file=/tmp/app_XXXX.xml) but I'll leave that up to you.
>>> I hope this gives you something to think over.
>>> Ashley,
>>> --
>>> Ashley Pittman, Bath, UK.
>>> Padb - A parallel job inspection tool for cluster computing
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