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

[Damian Kaliszan]

Hi,

OK. So this is clear now.
Maybe    you    will  be able to help the answer the question I raised
some time ago, why, when
submitting   a   slurm   job   and   setting   different   number   of
--cpus-per-task,  the  execution  times of ksp solver
(gmres type) vary when max number of iterations set to 100.000
and ksp, when finished, returns ksp.getIterationNumber() (in petsc4py)
equal to 900 (for some cases) and 100.000 for other.
It  looks  like  number of cpus per task influence the number of steps
the solver solves the equation. Is it possible at all?

Best,
Damian
 
W liście datowanym 1 lipca 2017 (22:23:19) napisano:
 
 
>> 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>
>> 



 
-------------------------------------------------------
Damian Kaliszan
 
Poznan Supercomputing and Networking Center
HPC and Data Centres Technologies
ul. Jana Pawła II 10
61-139 Poznan
POLAND
 
phone (+48 61) 858 5109
e-mail damian at man.poznan.pl
 www - http://www.man.poznan.pl/
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