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Shall I leave one core free when I run CFD simulation?

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Old   March 11, 2015, 23:46
Question Shall I leave one core free when I run CFD simulation?
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Pierre
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I use my 4 CPUs 32 cores (each CPU has 8cores) workstation to run CFD simulation by CFX. My workstation has Windows2008 R2 server system.

When I run CFX simulation with all of the 32 cores of my workstation, I turn on the task manager and find that there’s one core always used to deal with Windows system programs at the same time. That means there’s one core that is always not fully used for CFD calculation.

I suspect that that core will slow down overall CFD calculation greatly. Because the calculation by that core shall be much slower than the other cores and every time step the other cores will need to wait for that ‘slow’ core. So shall I always use 31 cores instead of 32 cores to maximize the calculation speed of my simulations?
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Old   March 12, 2015, 05:46
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Joern Beilke
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Just test your case with a different number of cores. I would suggest 2, 4 , 8 , 16 , 30 , 31 and 32 cores.

I would probably not use more than 30 cores on your configuration. But it depends both on your case and on your hardware.

It might turn out that it is faster to run 2 cases with 15 cores for each at the same time.
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