[Pw_forum] how does the calculation scales with number of processors

[mohnish pandey]

Thanks a lot Dr. Stefano for your reply.

On Fri, Dec 24, 2010 at 3:50 PM, Stefano de Gironcoli <degironc at sissa.it>wrote:

> It strongly depends on the particular calculation and on the
> parallelization strategy you choose. Linear scaling would be the ideal
> scaling which you never get.
> The things to keep in mind are  load balancing  and  communication
> overhead. This last is affected by your communication network latency
> and  bandwidth ... As a general rule the bigger the calculation the
> easier is to scale.
> It may be useful to have a look at the final timing summary of a
> calculation to see the fraction of time spent in communication (FFT
> scatter/gather and reduce operations) compared with the total wall clock
> time for your system and how this changes for different settings.
> Another factor to keep in mind is RAM memory as with certain
> parallelization strategies you can trade some speed with increased memory.
>
> stefano
>
> mohnish pandey wrote:
> > Dear QE users,
> >                          I am trying to see how the runtime scales with
> > number of processors. I did the same calculation using one node with
> eight
> > processors on one cluster and 8 nodes with total 56 processors on other
> > cluster but the time does not seem to scale linearly with the number of
> > processors. Can anybody give me an idea how does the time scale with
> number
> > of processors.
> > Thanks a lot in advance.
> >
> >
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-- 
Regards,
MOHNISH,
-----------------------------------------------------------------
Mohnish Pandey
Y6927262,5th Year dual degree student,
Department of Chemical Engineering,
IIT KANPUR, UP, INDIA
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