[mpich-discuss] Speed up issue with CFD solver.

[hritikesh semwal]

Hello,

I am developing a parallel CFD solver for unstructured grids with finite
volume explicit time integration method and the global mesh count is 97336
cells. I am trying to get the speed up results of my code but something
strange is happening. Following are my timing results after the second time
step with the different number of processors;

2 processors- 182.284 seconds
4 processors-  251.7035 seconds
8 processors- 190.8578 seconds
16 processors- 129.7989 seconds
24 processors- 121.0303 seconds
32 processors- 111.3772 seconds

I am not getting why there is a sharp rise in time from 2 processors to 4
processors and after that, it is decreasing. I had run the same code 2
weeks ago and at that time the results were different from the present
results and time was continuously decreasing at that time. Could someone
please help me with this matter by suggesting the probable cause/s of this
behaviour?

Thank you.
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