Hi Martin,

I always expected that if a variable named "foo" exists in two processes, it collects the same metric with the same semantics.

Yes, that is what I would hope for, too, but I think as it is written at the moment a fully standard compliant implementation does not have to work this way and there seems no viable way of finding out what the situation is, right?

When we wrote the paragraph we (or at least I) had in mind that the set of variables can be different (i.e., if "foo" exists on A, it does not have to exist on B) and the order can be different.

That is what I took from the first sentence in the advice to users, where it is explicitly stated that number and type of variables can change even between runs. That is fine, I guess, apart from the other issues that Michael raised on building a PAPI component.

Not sure if we can formalize this or if people would go along with it, but it would certainly be advantageous for the tools.

It would be a question for the MPI vendors, whether it would impose a serious restriction on their implementation to say that a name of a variable should not change semantics for a certain version of the implementation. But then again, what does "version" mean and how to define it ... :-/

However, having said that, I can actually envision scenarios where this would be hard to achieve. If you have a heterogeneous system (two architectures/networks or MPI bridging GPU and CPU) it may be a combination of two separate MPIs (with separate name spaces) or the same metric may have different meanings (similar to Flop counts having separate meanings on different architectures). I'd be curious to hear what our implementors think about that. In the homogeneous case, though, I would fully expect some consistency between processes.

As Michael pointed out in his reply, the "realm" idea could provide the means to define namespaces in a way that tools could query. However, I am still unsure whether something like this is overkill for the situation or whether it potentially solves only a non-existent problem. Cheers, Marc-Andre

On Jan 10, 2014, at 10:52 AM, Marc-Andre Hermanns <[email protected]> wrote:

...

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 Web www.grs-sim.de

Members: Forschungszentrum Jülich GmbH | RWTH Aachen University Registered in the commercial register of the local court of Düren (Amtsgericht Düren) under registration number HRB 5268 Registered office: Jülich Executive board: Prof. Marek Behr, Ph.D | Prof. Dr. Sebastian M. Schmidt

_______________________________________________ mpiwg-tools mailing list [email protected] http://lists.mpi-forum.org/mailman/listinfo.cgi/mpiwg-tools

_______________________________________________ mpiwg-tools mailing list [email protected] http://lists.mpi-forum.org/mailman/listinfo.cgi/mpiwg-tools

-- 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 Web www.grs-sim.de Members: Forschungszentrum Jülich GmbH | RWTH Aachen University Registered in the commercial register of the local court of Düren (Amtsgericht Düren) under registration number HRB 5268 Registered office: Jülich Executive board: Prof. Marek Behr, Ph.D | Prof. Dr. Sebastian M. Schmidt