PLMD::OpenMP::getNumThreads() returns only 1

[aalhossary]

In my Bias, I am trying to use OpenMP.
However, calling OpenMP::getNumThreads() I always receive 1, although the underlying Gromacs run reports 10 OMP threads per each one of the parallel simulations.

Is this related to #1380 ? i.e. Does Gromacs batch need more items to include?

Thank you

Amr

[Iximiel]

Hi amr

Sanity check: plumed config show | grep fopenmp returns something?

Try export PLUMED_NUM_THREADS=10 before running your simulation, it should do the trick

OpenMP::getNumThreads() is setup to return 1 unless the host program specifies a number or the user specifies a the environmental variable PLUMED_NUM_THREADS.

[aalhossary]

Hi Danielle,

Yes it does. It contains parameters in both CXXFLAGS and DYNAMIC_LIBS

export PLUMED_NUM_THREADS=10 should do the trick. However, I can not expect the right available number of OMP threads apriori.
Even if I do, there will be dynamic load balance which will change the distribution of calculation, and in a heterogenous environment (like ours) figuring out the right number will be impossible.

Therefore, we need a method to retrieve the right numOmpThreads from gromacs itself.

[GiovanniBussi]

@aalhossary you are right there is likely a bug. In the past, we were communicating the number of OpenMP threads from GROMACS. This has been lost somewhere, we should fix it.

For the moment you should use PLUMED_NUM_THREADS

Thanks for reporting!

[aalhossary]

It was last present in

plumed2/patches/gromacs-2024.3.diff/src/gromacs/mdrun/runner.cpp

Line 2335 in a1ea57f

plumed_cmd(plumedmain,"setNumOMPthreads",&nth);

Then this whole block (lines 2327-2351) was lost/removed in patch 2025.0

Could you add it to the patch, please?