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

[Danyang Su]

Hi Barry,

Thanks for the quick response. What I want to test is to check if OpenMP 
has any benefit when total degrees of freedoms per processor drops below 
5k. When using pure MPI my code shows good speedup if total degrees of 
freedoms per processor is above 10k. But below this value, the parallel 
efficiency decreases.

The petsc 3.6 change log indicates

  * Removed all threadcomm support including --with-pthreadclasses and
    --with-openmpclasses configure arguments

I guess petsc 3.5 version is the last version I can test, right?

Thanks,

Danyang


On 17-06-30 03:49 PM, Barry Smith wrote:
>    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>

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