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parallel computing doesn't speed up

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Old   March 15, 2013, 09:10
Default parallel computing doesn't speed up
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Md. Naimul Haque
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dear fomers,

greetings!

I am running kepsilon model using pisofoam on bluff body with 2D simulation in a Intel core 2 quad processor with 8gb ram. I have four local processors and the simulation is too heavy that to complete 1 iteration it takes 25 seconds. now,

1. if I decompose into 2 or 4 processors (like, 2 1 1 or 2 2 1) the speed is same. doesn't change at all.

2. another surprising thing is, if I decompose into 6 or 8 processors and run through mpi commad, it runs but the speed is same though I have 4 processors. how come it runs in 6 or 8 processors?

I have to have around 1223987 interations which would take 10 to 15 days if I can't use parallel computing effectively.

please help me, please. I will be waiting.
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Old   March 15, 2013, 11:35
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Hi !
A few questions :
What is the size of your domain ?
What was the exact command you used to run your case ? I used to forget the -parallel parameter at first.
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Old   March 16, 2013, 01:43
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Md. Naimul Haque
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thank u hiroshiman for ur inquiry.

my domain is 41Dx25D and width is extruded by openfoam, in the width direction there are single cell. I have total 6,00,000 cells to maintain y plus around 1 to 3. D is the height of domain.

I used simple dicomposition with the following command,

mpirun -np 4 pisoFoam -parallel

please help me, if u can. I am running out of time.
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Old   March 18, 2013, 10:55
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Hi,
with 6E6 cells, the problem should be large enough to be run over a few cpus.

Could you post the output of the solver on the few few first iterations to have a better idea of what's happening ?
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Old   March 21, 2013, 04:39
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Md. Naimul Haque
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Dear Hiroshiman,

Thank you for your query. I have reduced mesh number and running now, I think this allowable for me.

Thank you again.
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