[gmx-developers] omp usage

[titov_ai]

Hello.

I've used a gromacs template to create a program for MD trajectory 
analysis.
Omp threads were used in my code and it (omp) worked fine.
I've been using gromacs 2016, then updated it for 2019 and omp stopped 
working, the template seems to be the same, but omp stopped working.
After adding "SET( "CMAKE_CXX_FLAGS "-fopenmp")" it started to work once 
again. Although it should have been enabled through gromacs flags.
Then another problem popped up. I was testing my code on my laptop with 
8 therads - worked fine, on stationary computer with 4 therads - fine, 
but when i try to run it on a machine with 40 therads it shows 
unexpected behavior such as: system gives 20 threads for my program, 
while only one running the actual code, then when the code askes for 
threads the system gives another 20, but they are all on one core inside 
the previous main thread.
I suspect it has something to do with the number of avaliable threads 
and then it has nested therads.

how should i solve this problem ?

Best wishes,
Anatoly Titov, phd student, PNPI.