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September 8, 2010, 07:42 |
System time overhead in OF
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New Member
Join Date: Apr 2009
Posts: 26
Rep Power: 16 |
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? simpleFoam_job.jpg 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. simpleFoam_job2.jpg Can anyone explain the apparent serial overhead? Best regards, Ask |
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