Subject: Re: CCL:Scaling of G98 on Clusters

From: Christoph van Wüllen <[email-masked]>
Date: Fri, 31 Mar 2000 10:00:16 +0200

>Greetings everybody,
>
>this question goes to those who use Gaussian 98 (or maybe also other
>versions) on workstations clusters.
>
>
>Nodes	Effective speedup
>1	1
>4	3,93
>8	6,41
>10	8,55
>12	8,67
>16	7,9
>

Given a "serial work" of 1-2 per cent of the total CPU time, that is 
what you can expect according to Amdahl's law. This law even does NOT 
account for non-ideal communication, which maybe is responsible for 
the speedup going down from 12 to 16 processors.

Unless the diagonalization, orthogonalization etc. steps of SCF or 
DFT calculations are not done in parallel, it makes little sense to 
go far beyond 8 processors.
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