[mpich-discuss] Why do predefined MPI_Ops function elementwise in MPI_Accumulate, but not in MPI-1 routines?

[Jeff Hammond]

Yes, I saw "No MPI communication function may be called inside the
user function," but found this definition ambiguous and therefore
decided to ignore it.  What does this statementactually mean?  There
is no list of MPI operations that qualify as communications functions
and those that do not.  The describes operations as collective, local,
etc.

Is MPI_Win_lock a communication function?  If yes, what does it
communicate?  It is only supposed to define the start of an epoch, not
actually move data.  If no, why can it block on remote activity (for
an exclusive lock)?

Is MPI_Barrier(MPI_COMM_SELF) a communication function?
MPI_Reduce_local?  MPI_Cancel?

Maybe someone can point me to the table in the MPI standard where all
500+ functions are categorized as communication ones or not.

Jeff

On Mon, Apr 23, 2012 at 9:02 PM, Jed Brown <jedbrown at mcs.anl.gov> wrote:
> On Mon, Apr 23, 2012 at 20:54, Jeff Hammond <jhammond at alcf.anl.gov> wrote:
>>
>> If you implement your user-defined reduction using MPI_Accumulate
>> locally, does that not solve the problem?  In this case, whatever you
>> can do for MPI_Accumulate is valid for MPI_Reduce, right?
>>
>> my_reduction(..)
>> {
>> MPI_Win_create(MPI_COMM_SELF,..);
>> MPI_Accumulate(rank=me,..);
>> MPI_Win_free(MPI_COMM_SELF,..);
>> }
>
>
> "No MPI communication function may be called inside the user function."
>
> I think that means that these are not allowed, even when performed on
> MPI_COMM_SELF.
>
> Note that it's not the "hard" implementation that I'm complaining about,
> it's the need to translate between two different MPI_Ops that do exactly the
> same thing, but one that cannot be used with collectives and one that cannot
> be used with one-sided.
>
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-- 
Jeff Hammond
Argonne Leadership Computing Facility
University of Chicago Computation Institute
jhammond at alcf.anl.gov / (630) 252-5381
http://www.linkedin.com/in/jeffhammond
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