[Pw_forum] Predicting the cpu time usage for bigger system withour doing the simulation

[Michael Sullivan]

Hi,

I chose N=5 because the original post referred to 5 supercells. If your system is twice as big it will be 2**3, or 8 times bigger.

For the second part of your message, I don't have a good way to know in advance how it's going to perform. Usually I run some tests and build up experience.

If I understand you clearly, I would guess you're running out of memory when you run on a smaller number of nodes. If you're using pools for k-point parallelization, the memory doesn't scale.

Mike
michael at ihpc.a-star.edu.sg<mailto:michael at ihpc.a-star.edu.sg>
http://www.sullivan.sg/

From: pw_forum-bounces at pwscf.org [mailto:pw_forum-bounces at pwscf.org] On Behalf Of psavita at crlindia.com
Sent: Wednesday, July 21, 2010 12:51 PM
To: pw_forum at pwscf.org
Subject: Re: [Pw_forum] Pw_forum Digest, Vol 37, Issue 46 : Re: Predicting the cpu time usage for bigger system withour doing the simulation

Hello Mike,

"DFT usually scales as N^3 so I'd guess that it will take 5**3=125 times longer than the small system. You would probably gain somewhere due to fewer k-Points, etc. but that's my rough estimate."

Regarding your above comment, may I know how you choose N=5, is it just an example?
I have similar related question.
Is it possible to know the most appropriate compute resources for running a simulation without actually carrying out the same? My experience on a cluster is that by specifying a smaller number of nodes than the demand often results into node failure. Can this be avoided?

Thanks in advance for any clarification.

Regards,
Savita Pundlik
Applications Group : Computational Materials Simulations
Computational Research Laboratories Ltd.,
Taco House, Damle Path, Off Law College Road
Pune - 411004, India.


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