# Force Update on GPU

**URL:** <https://gromacs.bioexcel.eu/t/force-update-on-gpu/3043>\
**Category:** User discussions\
**Created:** [October 27, 2021, 10:39pm UTC](https://gromacs.bioexcel.eu/t/force-update-on-gpu/3043 "2021-10-27T22:39:06Z")\
**Posts on this page:** 1\
**Page:** 1

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**Author:** ![Masrul](https://dub1.discourse-cdn.com/flex017/user_avatar/gromacs.bioexcel.eu/masrul/32/234_2.png) [@Masrul](https://gromacs.bioexcel.eu/u/Masrul)\
**Post date:** [October 27, 2021, 10:39pm UTC](https://gromacs.bioexcel.eu/t/force-update-on-gpu/3043/1 "2021-10-27T22:39:06Z")

</div>

GROMACS version: 2020.6  
GROMACS modification: Yes/No

I am testing Gromacs on 4 GPUs/node. For 100K particle system with a single node, I am getting around ~50% performance boost with **-update gpu**. I am really excited about the number, but worried about the following warning,

““_This run will default to ‘-update gpu’ as requested by the GMX\_FORCE\_UPDATE\_DEFAULT\_GPU environment variable. GPU update with domain decomposition lacks substantial testing and should be used with caution._””

I wondering, what type of caution should I take before jumping into using **-update gpu**???. If there are any know issues or so?

#### Runtime settings

```bash
export GMX_GPU_DD_COMMS=true
export GMX_GPU_PME_PP_COMMS=true
export GMX_FORCE_UPDATE_DEFAULT_GPU=true

gmx mdrun \
    -ntmpi 8 -ntomp 8 \
    -pin on \
    -nb gpu \
    -bonded gpu \ 
    -pme gpu \
    -npme 1 \
    -deffnm final 

```

Thanks in advance fro your help.

Regards,  
Masrul