[gmx-users] (no subject)

[Fiona Reid]

Dear Gromacs users, 

Does anyone know how the total number of atoms is 
divided between processors? 

I have a system with 97787 elements, for 4 and 16 
processors the division of atoms/nodes seems to be ok:

Division over nodes in atoms:		(for 4 processors)
 24447 24447 24447 24446

Division over nodes in atoms:		(for 16 processors)
  6137  6118  6118  6110  6108  6108  6108  6108  6108  6108  6108  6111
6108  6111  6108  6110

However, for a 32 processor run or any run with more 
than 32 processors the division of atoms per node is no 
longer equal, e.g. 

Division over nodes in atoms:		(for 32 processors)
     0  6137  3036  3036  3036  3036  3058  3057  3057  3057  3057  3057
3057  3057  3057  3057  3057  3060  3057  3060  3057  3060  3057  3060
3057  3060  3057  3060  3057  3060  3057  3059
 
The first processor always gets zero atoms, the second 
processor always gets 6137 atoms and the remaining N-2 
processors get approx 91650/(N-2) atoms. 

Is this correct? how large an effect will the uneven 
atoms/node distribution have on the runtime? 

Regards, 

Fiona Reid