[Pw_forum] parallel FFTs - important MPI considerations

[Paolo Giannozzi]

On Monday 06 February 2006 18:08, Konstantin Kudin wrote:

>  Another potentially sucky part is "mpi_alltoallv" in the fft_scatter.
> This one depends on the cleverness of the MPI implementation
> significantly.

"mpi_alltoallv" is used instead of "mpi_alltoall" (without 'v') because
the slices into which the r-space grid is cut along direction 3 may 
not be all of the same size. Of course the special case in which all
the slices are equal could be quite easily treated with mpi_alltoall,
if it is really useful; or one could do copies and use mpi_alltoall. 
I would expect the library to take care of this, though.

>  Finally, has there been any activity on fftw3 ?

no, and I don't think there will be any, since fftw3 seems to be no
longer actively maintained and the preliminary results were not 
clearly in favor of fftw3

P.

-- 
Paolo Giannozzi             e-mail:  giannozz at nest.sns.it
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