[mpiwg-tools] MPI_T usage question: other sensors

[Michael Knobloch]

Hi all,

On 12/18/2013 05:09 PM, Marc-Andre Hermanns wrote:
> Hi Jeff,
>
> as a tools provider I would also like MPI_T to expose other sensors, as
> this means I don't have to support yet another metric interface. Not
> stacking a multitude of different metric interfaces on top of each other
> might also cut down on the overhead as you said.
>

Coming from the same tools group I unfortunately have to disagree with
Marc-Andre on that. Most of the tools out there (if not all relevant for
HPC) already have good support for PAPI, which does a great job of
providing a portable API to counters of all kind. And it's not an easy
job to do, so I'm not sure every MPI implementation would want to copy
that work. And that would be necessary if we'd only want to use MPI_T as
a single counter source, otherwise we'd still have to maintain both (in
fact, we'd for sure have to, as there are other parallel programming
paradigms out there as well which tools have to support).
So what I'd prefer is a PAPI component exposing the MPI relevant
counters via PAPI, that way the tools could benefit from that with very
little additional work.

> But could an implementation not expose such info right now? I thought
> the whole idea of not standardizing anything about counters, their names
> and semantics, is that implementations can expose whatever they care about.
>

Here I agree, from what I read in the current standard the interface
doesn't guarantee me anything. So at least some kind of
high-level/low-level interface as in PAPI would certainly be desirable.

-Michael
--
Michael Knobloch
Institute for Advanced Simulation (IAS)
Jülich Supercomputing Centre (JSC)
Telefon: +49 2461 61-3546
Telefax: +49 2461 61-6656
E-Mail: m.knobloch at fz-juelich.de
Internet: http://www.fz-juelich.de/jsc


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