The ABINIT Users Mailing List ( CLOSED )

["David M. Wood" <dmwood@mines.edu>]

Greetings all!

I have a couple of questions below.

I recently built abinip 5.7.3 on an 8-core 2008 Mac Pro and found a  
cheerily quasi-linear dependence of job speed on the number of  
processors used.  But I saw no improvement at all in going from 4 to 5  
processors, or from 6 to 7.  T (Top panel of attached PDF graphic,  
where more details are given.)  The machine has 4 processors each

Attachment: NProcSumm.pdf
Description: Adobe PDF document

G1

on 2 dies.

1. Any idea why the improvement is not monotonic in the number of  
processors?

I found that the tail end of the iteration history (as measured by max  
grad of the force/grad in the optcell=2 portion of my runs) differed  
slightly depending on the number of processors.  (Bottom panel of PNG  
graphic.  I found no physically significant changes in cell dimensions  
and far less in the total energy, so I'm not worried.)

2. Does this ever become an issue when dealing with hundreds or  
thousands of processors in a cluster, where I'm heading, and is this  
normal behavior?

Many thanks!
DMW

David M. Wood
dmwood@Mines.EDU