[MPICH] MPI_REDUCE with MPI_IN_PLACE fails with memory error

[Rusty Lusk]

I believe our error-checking profiling library detects this error,  
doesn't it?

On Mar 13, 2007, at 11:08 AM, Anthony Chan wrote:

>
> We have no access to intel 9.x compilers yet, can't directly verify  
> the
> reported problem.  However you may be using MPI_IN_PLACE incorrectly
> in non-root process.
>
> On Tue, 13 Mar 2007, Martin Kleinschmidt wrote:
>
>> The corresponding lines of code are:
>>
>> #################
>> #ifdef PARALLEL
>>          if (myid .eq. 0) then
>>             call MPI_Reduce(MPI_IN_PLACE, vecf2(1),
>>      $           n*nneue,
>>      $           MPI_double_precision, MPI_SUM, 0,
>>      $           MPI_Comm_World, MPIerr)
>>          else
>>             call MPI_Reduce(vecf2(1),MPI_IN_PLACE,
>>      $           n*nneue,
>>      $           MPI_double_precision, MPI_SUM, 0,
>>      $           MPI_Comm_World, MPIerr)
>>          endif
>> #endif
>
> Try calling MPI_Reduce with MPI_IN_PLACE in send buffer in all  
> ranks, i.e.
>
>               call MPI_Reduce(MPI_IN_PLACE, vecf2(1),
>        $           n*nneue,
>        $           MPI_DOUBLE_PRECISION, MPI_SUM, 0,
>        $           MPI_COMM_WORLD, MPIerr)
>
>
> A.Chan
>
>> #################
>> with n*nneue = 76160987, and 76160987*8 = 609287896, about 600 MB
>>
>> The point is: I thought, I could avoid the need for allocationg
>> additional memory by using MPI_IN_PLACE, which obviously does not  
>> work.
>>
>> - do I use MPI_IN_PLACE in the right way?
>> - why does MPI_IN_PLACE need additional memory?
>> - is it possible to rewrite this code in a way that eliminates the  
>> need
>>   for allocating additional memory? This part of the code is not
>>   time-critical - it is executed once every few hours.
>>
>> (I'm using mpich2-1.0.5p2, Intel fortran compiler 9.1.040, Intel C
>> compiler 9.1.045 for compiling both mpich and my code)
>>
>>    ...martin
>>
>>
>