# Multi-walker awh simulation using one gpu

**URL:** <https://gromacs.bioexcel.eu/t/multi-walker-awh-simulation-using-one-gpu/9986>\
**Category:** User discussions\
**Tags:** mdrun, awh\
**Created:** [August 26, 2024, 12:58am UTC](https://gromacs.bioexcel.eu/t/multi-walker-awh-simulation-using-one-gpu/9986 "2024-08-26T00:58:35Z")\
**Posts on this page:** 3\
**Page:** 1

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**Author:** ![roozi](https://avatars.discourse-cdn.com/v4/letter/r/958977/32.png) [@roozi](https://gromacs.bioexcel.eu/u/roozi)\
**Post date:** [August 26, 2024, 12:58am UTC](https://gromacs.bioexcel.eu/t/multi-walker-awh-simulation-using-one-gpu/9986/1 "2024-08-26T00:58:35Z")

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GROMACS version:2024.2  
GROMACS modification: No

Hi,  
I am trying to run a multi-walker awh simulation with 2 walkers and a single bias. I wish to use my pc with one gpu and 32 cores to run it. So to that end, i have compiled gmx\_mpi and then enabled nvidia MPS (Multi-Process Service) with “nvidia-cuda-mps-control -d” and then ran the following command line script:

> gmx\_mpi mdrun -deffnm awh-multi -update gpu -nb gpu -pme gpu -bonded gpu -multidir 0 1 -npme -1

out of which i got the following error msg:

```auto
Feature not implemented:
PME tasks were required to run on GPUs with multiple ranks but the -npme
option was not specified. A non-negative value must be specified for -npme.

```

also tried to rerun the md simulation without the -npme flag , and still got the same error.  
is there anyway to run an awh simulation with 2 walkers on a single gpu ?

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<div class="post-metadata">

**Author:** ![MagnusL](https://dub1.discourse-cdn.com/flex017/user_avatar/gromacs.bioexcel.eu/magnusl/32/2380_2.png) [@MagnusL](https://gromacs.bioexcel.eu/u/MagnusL)\
**Post date:** [August 26, 2024, 6:31am UTC](https://gromacs.bioexcel.eu/t/multi-walker-awh-simulation-using-one-gpu/9986/2 "2024-08-26T06:31:33Z")

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Try with mpirun, e.g.  
`mpirun -np 2 gmx_mpi mdrun -multidir 0 1 -update gpu -nb gpu -pme gpu -bonded gpu -deffnm awh-multi -cpi`

See [Useful mdrun features - GROMACS 2024.2 documentation](https://manual.gromacs.org/current/user-guide/mdrun-features.html#running-multi-simulations) for more information.

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<div class="post-metadata">

**Author:** ![roozi](https://avatars.discourse-cdn.com/v4/letter/r/958977/32.png) [@roozi](https://gromacs.bioexcel.eu/u/roozi)\
**Post date:** [August 27, 2024, 3:58am UTC](https://gromacs.bioexcel.eu/t/multi-walker-awh-simulation-using-one-gpu/9986/3 "2024-08-27T03:58:38Z")

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yeah. my mistake not to use mpirun -np option. now it is working. tnx.