[gmx-users] Regarding getting good performance for mdrun

[Dilip.H.N]

Hello all,
My workstation has 1 node with total 24 cores, 48 logical cores.

1] I gave the command as: gmx mdrun -v -s abc.tpr -deffnm abc

I got few messages as:-

NOTE: Parallelization is limited by the small number of atoms,
      only starting 16 thread-MPI ranks.
      You can use the -nt and/or -ntmpi option to optimize the number of
threads.
Using 16 MPI threads
Using 3 OpenMP threads per tMPI thread
WARNING: This run will generate roughly 51484 Mb of data
starting mdrun 'abc system'
1000000 steps,   1000.0 ps.
step 999900, remaining wall clock time:     0 s          imb F 10%
Writing final coordinates.
step 1000000, remaining wall clock time:     0 s
 Average load imbalance: 11.0 %
 Part of the total run time spent waiting due to load imbalance: 1.7 %
NOTE: 28 % of the run time was spent communicating energies,
      you might want to use the -gcom option of mdrun

2] and then if i give the command as: gmx mdrun -v -s abc.tpr -deffnm
abc -ntmpi 6 -ntomp 8
I got:
Using 6 MPI threads
Using 8 OpenMP threads per tMPI thread
step 36800, will finish Sat May  5 12:42:12 2018 imb F  6%

So, My questions are:-
a) Does the simulation run just with gmx mdrun, effect on the
trajectories/output files
b) "28 % of the run time was spent communicating...." Has it affected the
resulting output..??
c) what does this imb F means..?? and what is the significance of the
percentage (say 1.7%) states/defines..??
c) Any other information regarding these are highly beneficial..

Thank you.
---
With Best Regards,

Dilip.H.N
PhD Student.