[Trilinos-Users] Epetra vs. Tpetra

Frey Matthias (PSI) matthias.frey at psi.ch
Tue Oct 24 08:58:14 EDT 2017

Hi Bart

Thanks a lot for your reply. I tried out, but unfortunately it does not help in my case.



Von: Bart Janssens [bart at bartjanssens.org]
Gesendet: Dienstag, 24. Oktober 2017 14:50
An: Frey Matthias (PSI); trilinos-users at trilinos.org
Betreff: Re: [Trilinos-Users] Epetra vs. Tpetra

Hi Matthias,

I haven't looked at your code in detail, but I had this sort of thing happen when OpenMP was on for Tpetra (thus conflicting with MPI). You can switch it off at runtime by setting the environment variable OMP_NUM_THREADS=1.



On Tue, Oct 24, 2017 at 1:27 PM Frey Matthias (PSI) <matthias.frey at psi.ch<mailto:matthias.frey at psi.ch>> wrote:
Dear Trilinos-Users,

I'm facing a performance issue that I do not understand and would appreciate your help.

I implemented a Poisson solver for block-structured grids using Epetra. In order to use newer features I wanted to replace Epetra with Tpetra
but the execution slowed down extremely.

In order to reproduce this result I implemented a small test example where the time for the initialization of the Poisson matrix (3D problem) is measured.
Btw, I initialize the matrix as I do it in the original code, but there I use another library that does the adaptive mesh refinement etc., hence, I iterate over boxes that specify the domain. Each core should get another box.

When I run the example with 4 cores and 128 grid points in each direction, Epetra is 10 times faster than Tpetra. I do not understand what I'm doing wrong.

$ mpirun -np 4 testEpetra 128
Number of processes: 4
Dimension: 128
Elapsed time: 4.5793 seconds.

$ mpirun -np 4 testTpetra 128
Number of processes: 4
Dimension: 128
Elapsed time: 42.6839 seconds.


I attached a tar-file that contains both *.cpp files a readme. Furthermore, I provide everything to build the examples using CMake.

Best regards,

Matthias Frey

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