# Why performance is decrease when i am submitting the multiple jobs parallely?

**URL:** <https://gromacs.bioexcel.eu/t/why-performance-is-decrease-when-i-am-submitting-the-multiple-jobs-parallely/2861>\
**Category:** User discussions\
**Tags:** mdrun\
**Created:** [September 23, 2021, 10:03am UTC](https://gromacs.bioexcel.eu/t/why-performance-is-decrease-when-i-am-submitting-the-multiple-jobs-parallely/2861 "2021-09-23T10:03:03Z")\
**Posts on this page:** 1\
**Page:** 1

<div class="post-metadata">

**Author:** ![renu](https://avatars.discourse-cdn.com/v4/letter/r/7c8e57/32.png) [@renu](https://gromacs.bioexcel.eu/u/renu)\
**Post date:** [September 23, 2021, 10:03am UTC](https://gromacs.bioexcel.eu/t/why-performance-is-decrease-when-i-am-submitting-the-multiple-jobs-parallely/2861/1 "2021-09-23T10:03:04Z")

</div>

GROMACS version:2020.1  
GROMACS modification: Yes/No  
Here post your question  
Dear gromacs users,  
I am doing a performance check using gromacs 2020.1.  
I have taken a simulation system consisting of 38706 atoms. I have 2 nodes in my server, each node has 256 cores so total 512 cores we have.  
I am doing a performance check only at one node (256 cores). When I occupy 16 cores out of 256 cores (using ntomp=1,2,4 and ntmpi=16,8,4) gromacs performance is approx 40 ns/day. Since I have 256 cores, I submitted identical 16 jobs to occupy all cores. While doing this I did use -pin, -pinoffset and -pinstride options to take care that each job will be running on separate cores. Not only this but also I did manually check but submitting one job at a time to confirm that each job is occupying different cores. (e.g. job1 is running on 1-8 and 129-136 cores, job2 is running on 17-24 and 137-144 cores and so on. Because pinstride was 1) After doing all the checks when I am submitting all 16 possible jobs to occupy 256 cores, performance for each job is drastically decreasing from ~40 ns/day to ~17 ns.day.

I need your help here to figure out why this is happening? What is the best way to submit such 16 jobs in parallel so that I shall get optimum performance?

Commands I am executing:  
job1:  
mpirun -np 16 /apps/gromacs/gromacs-2020.1/build\_mpi/bin/gmx\_mpi mdrun -s …/…/…/…/218K-8mics\_1000ps\_6nm-2fs.tpr -v -deffnm test1 -nsteps 1000 -ntomp 1 -pin on -pinoffset 0 -pinstride 1

job2:  
mpirun -np 16 /apps/gromacs/gromacs-2020.1/build\_mpi/bin/gmx\_mpi mdrun -s …/…/…/…/218K-8mics\_1000ps\_6nm-2fs.tpr -v -deffnm test1 -nsteps 1000 -ntomp 1 -pin on -pinoffset 16 -pinstride 1

job 3:  
mpirun -np 16 /apps/gromacs/gromacs-2020.1/build\_mpi/bin/gmx\_mpi mdrun -s …/…/…/…/218K-8mics\_1000ps\_6nm-2fs.tpr -v -deffnm test1 -nsteps 1000 -ntomp 1 -pin on -pinoffset 32 -pinstride 1  
and so on