Dears,
I have the following doubt:
Considering the following scenario:
I have an executable Lammps compiled with the USER-OMP package and the CCFLAGS -fopenmp, among others.
If we set the environment variable OMP_NUM_THREADS = 2 and run Lammps as follows:
mpirun -np 4 lammps < in.script (the USER-OMP package is not activated and / omp is not included in the script)
The log file says something like:
using 2 OpenMP thread(s) per MPI task
.
.
Performance: 43658.822 tau/day, 101.062 timesteps/s
100.9% CPU use with 4 MPI tasks x 2 OpenMP threads
Although the USER-OMP package was not activated the simulation was run with 2 OpenMP threads. How does Lammps resolve this request? Is there a default USER-OMP configuration when the variable OMP_NUM_THREADS is set, even though the package is not explicitly invoked?
regards
Dears,
I have the following doubt:
Considering the following scenario:
I have an executable Lammps compiled with the USER-OMP package and the
CCFLAGS -fopenmp, among others.
If we set the environment variable OMP_NUM_THREADS = 2 and run Lammps as
follows:
mpirun -np 4 lammps < in.script (the USER-OMP package is not activated and /
omp is not included in the script)
The log file says something like:
using 2 OpenMP thread(s) per MPI task
.
.
Performance: 43658.822 tau/day, 101.062 timesteps/s
100.9% CPU use with 4 MPI tasks x 2 OpenMP threads
Although the USER-OMP package was not activated the simulation was run with
2 OpenMP threads. How does Lammps resolve this request? Is there a default
USER-OMP configuration when the variable OMP_NUM_THREADS is set, even though
the package is not explicitly invoked?
whether styles from the USER-OMP package are invoked in this case or
not is completely irrelevant.
you have an OpenMP capable executable and you have set OMP_NUM_THREADS
to 2, that means you have requested 2 threads per MPI rank and the
LAMMPS output reflects that. That you are not using any OpenMP enabled
code is your choice and the ~100% CPU use reflects that, too.
mind you, USER-OMP is not the only provider of OpenMP capable code in
LAMMPS, there is the KOKKOS package and USER-INTEL as well and a few
select individual styles, that have OpenMP directives included.
axel.