# Gromacs run only on 1 processor without using all threads

**URL:** <https://gromacs.bioexcel.eu/t/gromacs-run-only-on-1-processor-without-using-all-threads/9530>\
**Category:** User discussions\
**Created:** [June 28, 2024, 8:28am UTC](https://gromacs.bioexcel.eu/t/gromacs-run-only-on-1-processor-without-using-all-threads/9530 "2024-06-28T08:28:54Z")\
**Posts on this page:** 3\
**Page:** 1

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**Author:** ![Yel21](https://avatars.discourse-cdn.com/v4/letter/y/b2d939/32.png) [@Yel21](https://gromacs.bioexcel.eu/u/Yel21)\
**Post date:** [June 28, 2024, 8:28am UTC](https://gromacs.bioexcel.eu/t/gromacs-run-only-on-1-processor-without-using-all-threads/9530/1 "2024-06-28T08:28:54Z")

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GROMACS version: 2023.3  
GROMACS modification: No  
Hello Gromacs users,

I built Gromacs 2023.3 on Ubuntu 24.04 with pre-installed `libomp-dev` using such code

`cmake .. -DGMX_GPU=CUDA -DGMX_PREFER_STATIC_LIBS=OFF -DGMXAPI=OFF -DGMX_BUILD_OWN_FFTW=ON -DCUDA_TOOLKIT_ROOT_DIR=/usr/local/cuda -DCMAKE_INSTALL_PREFIX=/home/xxx/progs/gromacs_2023_3 -DGMX_DEFAULT_SUFFIX=OFF -DGMX_BINARY_SUFFIX=_2023_3 -DGMX_LIBS_SUFFIX=_2023_3 make -j 20 make install `  
The installation of Gromacs did not cause any problems. However, when I run gromacs:

`gmx_2023_3 mdrun -v -deffnm press600 -bonded gpu -nb gpu -pme gpu -s topol_600.tpr -cpi press600.cpt`

In the log file, I see that

```auto
PME tasks will do all aspects on the GPU
Using 1 MPI thread
Using 32 OpenMP threads

```

Nevertheless, the `nvtop` or `glances` only show that 1 processor run on maximum 100% performance.  
Could you please suggest a solution to this problem.

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**Author:** ![scinikhil](https://dub1.discourse-cdn.com/flex017/user_avatar/gromacs.bioexcel.eu/scinikhil/32/3483_2.png) [@scinikhil](https://gromacs.bioexcel.eu/u/scinikhil)\
**Post date:** [June 28, 2024, 9:08pm UTC](https://gromacs.bioexcel.eu/t/gromacs-run-only-on-1-processor-without-using-all-threads/9530/2 "2024-06-28T21:08:54Z")

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can you share your system information and log file. You have offloaded all the calculations to the GPU, though

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**Author:** ![hess](https://dub1.discourse-cdn.com/flex017/user_avatar/gromacs.bioexcel.eu/hess/32/416_2.png) [@hess](https://gromacs.bioexcel.eu/u/hess)\
**Post date:** [July 4, 2024, 11:45am UTC](https://gromacs.bioexcel.eu/t/gromacs-run-only-on-1-processor-without-using-all-threads/9530/3 "2024-07-04T11:45:00Z")

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When everything runs on the GPU, only one thread will be active most of the time on the CPU, so most cores will be idle.