[Trilinos-Users] Epetra vs. Tpetra

[Bart Janssens]

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.

Cheers,

Bart

On Tue, Oct 24, 2017 at 1:27 PM Frey Matthias (PSI) <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.
>
>
> EPETRA
> ==================
> $ mpirun -np 4 testEpetra 128
> Number of processes: 4
> Dimension: 128
> Elapsed time: 4.5793 seconds.
>
>
> TPETRA
> ==================
> $ mpirun -np 4 testTpetra 128
> Number of processes: 4
> Dimension: 128
> Elapsed time: 42.6839 seconds.
>
>
>
> Modules
> --------------
> gcc/5.4.0
> openmpi/1.10.4
> trilinos/12.10.1
>
>
> 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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