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askjak September 8, 2010 06:42

System time overhead in OF
2 Attachment(s)
Hi all,

I have noticed that on our cluster that openfoam have a very different cpu usage compared to other cfd codes.

In OF a large fraction of the time is spend in system cpu time compared to user cpu time. Other cfd codes we have had our hands on spend almost 100% of the time in user cpu.

I have made a small case based on the angledDuct case with 178000 cells using simpleFoam. The case was constructed so no IO was performed.

In serial more than 30% of the time is spend in system time. Is this an overhead due to the dynamic memory allocation in OF?

Attachment 4644

When running the case in parallel (2 nodes) the system time CPU time fraction drops to a few percent which is difficult for me to understand.

Attachment 4645

Can anyone explain the apparent serial overhead?

Best regards,

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