# Mdrun options

**URL:** <https://gromacs.bioexcel.eu/t/mdrun-options/838>\
**Category:** User discussions\
**Created:** [September 20, 2020, 4:18pm UTC](https://gromacs.bioexcel.eu/t/mdrun-options/838 "2020-09-20T16:18:31Z")\
**Posts on this page:** 2\
**Page:** 1

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**Author:** ![kw24](https://avatars.discourse-cdn.com/v4/letter/k/7feea3/32.png) [@kw24](https://gromacs.bioexcel.eu/u/kw24)\
**Post date:** [September 20, 2020, 4:18pm UTC](https://gromacs.bioexcel.eu/t/mdrun-options/838/1 "2020-09-20T16:18:31Z")

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GROMACS version: 2020.3  
GROMACS modification: No

Hi there,

If I want to run 4 simulations at the same time with a computer built with 4 cores, what mdrun options should I enable to optimize performance?

Does adding `-nt 1 -pin on` for each simulation localize each of them to 1 core to make everything run faster? Or should I just omit `-nt` altogether? Or are those 2 options not correct at all?

Thanks!

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**Author:** ![pjohansson](https://dub1.discourse-cdn.com/flex017/user_avatar/gromacs.bioexcel.eu/pjohansson/32/316_2.png) [@pjohansson](https://gromacs.bioexcel.eu/u/pjohansson)\
**Post date:** [September 20, 2020, 6:17pm UTC](https://gromacs.bioexcel.eu/t/mdrun-options/838/2 "2020-09-20T18:17:53Z")

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Hello,

yes, `-nt 1` sets the number of cores for the simulation to 1, and `-pin on` pins the simulation to one specific core. You should also use `-pinoffset` to set which core will be used. For 1 core per simulation, `-pinoffset 0` sets the simulation to core #1, `-pinoffset 1` to #2, etc.