[mpiwg-tools] MPI_T names of variables

[Marc-Andre Hermanns]

Dear all,

I hope all of you had a good start into the new year.

Let me apologize in advance for the lengthy text following.

I am currently in the discussion with the developers of the metric
modules for Scalasca and Score-P, and I think we need some
clarification. Please correct me in my understanding if anything of the
following is not correct.

Here is the current quote of the advice to users in the ticket PDF:

"[...]Further, there is no guarantee that number of variables, variable
indices, and variable names are the same across processes."

I read the following out of this:
A variable indicating a metric X may be called "foo" on one process and
"bar" on another.

Is that correct?

a) How should a tool aggregate and correlate metrics if there is no way
on knowing which belong together (after all indices and names are
different)?

b) Does this allow the namespaces of metrics to overlap?
If the variable for metric X is "foo" on one process and "bar" on
another. Is the other process allowed to have a variable "foo" that
actually reports some different metric? How will a tool get the difference?

I know that the new "Advice to implementers" is supposed to clarify
this. But I am unsure whether making this a sole "quality of
implementation" issue will work for providers of portable tools.

Also, with differences among runs, tools like the Cube Algebra (where
you can compute averages of multiple measurements) do not work anymore,
as Cube will not know whether "foo" of run one correlates to "foo" of
run two, rendering the whole tool moot.

Cheers,
Marc-Andre
-- 
Marc-Andre Hermanns
German Research School for
Simulation Sciences GmbH
c/o Laboratory for Parallel Programming
52062 Aachen | Germany

Tel +49 241 80 99753
Fax +49 241 80 6 99753
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