[ET Trac] [Einstein Toolkit] #1831: Enable MPI in FFTW3

[Einstein Toolkit]

#1831: Enable MPI in FFTW3
------------------------------------+---------------------------------------
  Reporter:  eschnett               |       Owner:                     
      Type:  enhancement            |      Status:  reopened           
  Priority:  optional               |   Milestone:                     
 Component:  EinsteinToolkit thorn  |     Version:  development version
Resolution:                         |    Keywords:                     
------------------------------------+---------------------------------------

Comment (by knarf):

 Assuming the thorn detects an external fftw library, that was not build
 with mpi - what should happen then? It seems that with the current patch
 libfftw3_mpi(.so) would be added as library without checking that a) this
 is needed (it was not so far) and b) it actually exists.

 In fact, I do get the expected linker error with the patch: cannot find
 -lfftw3_mpi

 mpi bindings for fftw3 might need to be installed separately, e.g., I have
 libfftw3-dev [1] installed, but not libfftw3-mpi-dev [2].

 [1] https://packages.debian.org/jessie/amd64/libfftw3-dev/filelist
 [2] https://packages.debian.org/jessie/amd64/libfftw3-mpi-dev/filelist

 We would need to warn users if we would the ET require MPI bindings for
 fftw (which we would if we assume them to be there if MPI is used).

 Another issue might be that the installed MPI bindings for fftw might not
 be linked against the version of MPI that Cactus is configured to use. We
 would have to check for that. libfftw3-mpi on my system seems to use
 openmpi, which happens to be the MPI I also use for Cactus. That fftw3-mpi
 package for Ubuntu also uses openmpi, while the simfactory configuration
 for ubuntu advises users to install mpich2 (but I checked that using
 openmpi would also work).

 We could of course only add the MPI bindings for the case when FFTW is
 build by Cactus, but then thorns shouldn't rely on them being present,
 which would defeat the purpose I would guess.

 All these complications make me wonder if this change is worth the
 trouble. They might, but what would they be used for?

-- 
Ticket URL: <https://trac.einsteintoolkit.org/ticket/1831#comment:4>
Einstein Toolkit <http://einsteintoolkit.org>
The Einstein Toolkit