[Mpi-22] determine if running in a heterogenous environment

[Richard Treumann]

The simple question seems to be:  Can MPI_BYTE be used safely on this
communicator?  If even one datatype requires translation then the answer is
"no".  How about just calling the per communicator attribute something like
"MPI_BYTE_SAFE" and leave other debates about the meaning of heterogeneous
aside?

There is clearly room to add complexity but is there a real need? It seems
to me that communicator attribute "MPI_BYTE_SAFE" provides 99% of the value
and is easy to do.

Dick Treumann  -  MPI Team/TCEM
IBM Systems & Technology Group
Dept 0lva / MS P963 -- 2455 South Road -- Poughkeepsie, NY 12601
Tele (845) 433-7846         Fax (845) 433-8363

mpi-22-bounces_at_[hidden] wrote on 03/03/2008 01:24:11 PM:

> On Mar 3, 2008, at 12:54 PM, Dries Kimpe wrote:
>
> >> Narrowing the scope to "whether translation functionality is
> >> required"
> >> is good.  But note that whether the translation functionality is used
> >> may be specific to a given (communicator,peer,datatype) tuple.
> >
> > You're right that this depends on the communicator and on the peer;
>
> ...and the datatype.
>
> > It would not be uncommon to have one 'different (memory representation
> > wise)' node in the communicator. This could be a login node, a
> > visualisation node, ...
> >
> > So, from a performance point of view (and also for the mpi
> > implementation
> > internally), it's actually better to record this information for
> > (communicator, source, dest). However, my main reason for this
> > proposal
> > was to enable an application that doesn't care about datatypes
> > (might be
> > more common than you'd think, looking at some of the mpi-subset
> > ideas) to
> > abort execution if it detects that data conversion is needed when
> > communicating to its peers.
>
>
> My point is that some datatypes may require translation while others
> may not.  It's not always just endian differences -- sometimes there's
> floating point representation differences, or size differences (e.g.,
> sizeof(int) != sizeof(int)).
>
> --
> Jeff Squyres
> Cisco Systems
>
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