[petsc-users] Is OpenMP still available for PETSc?

[Barry Smith]

> On Jul 1, 2017, at 3:15 PM, Damian Kaliszan <damian at man.poznan.pl> wrote:
> 
> Hi, 
> So... - - with-openmp=0/1 configuration option seems to be useless?... 

   It merely enables the compiler flags for compiling with OpenMP; for example if your code has OpenMP in it.

> In one of my previous messages I wrote that, when openmp enabled, and OMP_NUM_THREADS set, I notice different timings for ksp solver. Strange....? 

   For the PETSc part yes number of threads shouldn't matter since PETSc would only use 1.
> 
> 
> Best, 
> Damian
> W dniu 1 lip 2017, o 00:50, użytkownik Barry Smith <bsmith at mcs.anl.gov> napisał:
> 
>   The current version of PETSc does not use OpenMP, you are free to use OpenMP in your portions of the code of course. If you want PETSc using OpenMP you have to use the old, unsupported version of PETSc. We never found any benefit to using OpenMP.
> 
>    Barry
> 
>  On Jun 30, 2017, at 5:40 PM, Danyang Su <danyang.su at gmail.com> wrote:
>  
>  Dear All,
>  
>  I recalled there was OpenMP available for PETSc for the old development version. When google "petsc hybrid mpi openmp", there returned some papers about this feature. My code was first parallelized using OpenMP and then redeveloped using PETSc, with OpenMP kept but not used together with MPI. Before retesting the code using hybrid mpi-openmp, I picked one PETSc example ex10 by adding "omp_set_num_threads(max_threads);" under PetscInitialize.
>  
>  The PETSc is the current development version configured as follows
>  
>  --with-cc=gcc --with-cxx=g++ --with-fc=gfortran --with-debugging=0 --CFLAGS=-fopenmp --CXXFLAGS=-fopenmp --FFLAGS=-fopenmp COPTFLAGS="-O3 -march=native -mtune=native" CXXOPTFLAGS="-O3 -march=native -mtune=native" FOPTFLAGS="-O3 -march=native -mtune=native" --with-large-file-io=1 --download-cmake=yes --download-mumps --download-scalapack --download-parmetis --download-metis --download-ptscotch --download-fblaslapack --download-mpich --download-hypre --download-superlu_dist --download-hdf5=yes --with-openmp --with-threadcomm --with-pthreadclasses --with-openmpclasses
>  
>  The code can be successfully compiled. However, when I run the code with OpenMP, it does not work, the time shows no change in performance if 1 or 2 threads per processor is used. Also, the CPU/Threads usage indicates that no thread is used.
>  
>  I just wonder if OpenMP is still available in the latest version, though it is not recommended to use.
>  
>  mpiexec -n 2 ./ex10 -f0 mat_rhs_pc_nonzero/a_react_in_2.bin -rhs mat_rhs_pc_nonzero/b_react_in_2.bin -ksp_rtol 1.0e-20 -ksp_monitor -ksp_error_if_not_converged -sub_pc_factor_shift_type nonzero -mat_view ascii::ascii_info -log_view -max_threads 1 -threadcomm_type openmp -threadcomm_nthreads 1
>  
>  KSPSolve               1 1.0 8.9934e-01 1.0 1.03e+09 1.0 7.8e+01 3.6e+04 7.8e+01 69 97 89  6 76  89 97 98 98 96  2290
>  PCSetUp                2 1.0 8.9590e-02 1.0 2.91e+07 1.0 0.0e+00 0.0e+00 0.0e+00  7  3  0  0  0   9  3  0  0  0   648
>  PCSetUpOnBlocks        2 1.0 8.9465e-02 1.0 2.91e+07 1.0 0.0e+00 0.0e+00 0.0e+00  7  3  0  0  0   9  3  0  0  0   649
>  PCApply               40 1.0 3.1993e-01 1.0 2.70e+08 1.0 0.0e+00 0.0e+00 0.0e+00 24 25  0  0  0  32 25  0  0  0  1686
>  
>  mpiexec -n 2 ./ex10 -f0 mat_rhs_pc_nonzero/a_react_in_2.bin -rhs mat_rhs_pc_nonzero/b_react_in_2.bin -ksp_rtol 1.0e-20 -ksp_monitor -ksp_error_if_not_converged -sub_pc_factor_shift_type nonzero -mat_view ascii::ascii_info -log_view -max_threads 2 -threadcomm_type openmp -threadcomm_nthreads 2
>  
>  KSPSolve               1 1.0 8.9701e-01 1.0 1.03e+09 1.0 7.8e+01 3.6e+04 7.8e+01 69 97 89  6 76  89 97 98 98 96  2296
>  PCSetUp                2 1.0 8.7635e-02 1.0 2.91e+07 1.0 0.0e+00 0.0e+00 0.0e+00  7  3  0  0  0   9  3  0  0  0   663
>  PCSetUpOnBlocks        2 1.0 8.7511e-02 1.0 2.91e+07 1.0 0.0e+00 0.0e+00 0.0e+00  7  3  0  0  0   9  3  0  0  0   664
>  PCApply               40 1.0 3.1878e-01 1.0 2.70e+08 1.0 0.0e+00 0.0e+00 0.0e+00 24 25  0  0  0  32 25  0  0  0  1692
>  
>  Thanks and regards,
>  
>  Danyang
>  
>  
>  <ex10.c><makefile.txt>
>