[OpenFOAM.com] openFOAM v2012 slower execution than v1812

Dikkeunit · April 30, 2021, 03:39

Hey all,
I am having a weird issue that the new installment of openFOAM seems to be consistently twice as slow as v1812.
We run on a remote Linux server with 128 cores and I have tested both old and new installment with 60 cores parallel execution. All functions e.g. snappyHexMesh, porousSimpleFoam and postProcess have the same issue. I was wondering if anyone also had a similar issue?
Thank you

olesen · May 3, 2021, 02:00

Same hardware, similar compilation?
Check the single core speeds, next check your mpi. I have heard of slowdowns with particular versions of intel-mpi (I think the latest is good), but I don't know any real details.

Dikkeunit · July 2, 2021, 09:19

Hey, sorry for not responding, it has slipped my mind that I had opened this thread. I have found the problem, which was that the server used more cores than it physically had. This came to mind when we installed a new version of openMPI, which said we were using more cores than were available! We always assumed also the virtual cores were used by openFOAM, but this is not the case, apparently. So if someone is also struggling with the speed, check your hardware!

Thanks

April 30, 2021, 03:39	openFOAM v2012 slower execution than v1812	#1
Dikkeunit New Member Max Join Date: Sep 2019 Posts: 8 Rep Power: 7	Hey all, I am having a weird issue that the new installment of openFOAM seems to be consistently twice as slow as v1812. We run on a remote Linux server with 128 cores and I have tested both old and new installment with 60 cores parallel execution. All functions e.g. snappyHexMesh, porousSimpleFoam and postProcess have the same issue. I was wondering if anyone also had a similar issue? Thank you

July 2, 2021, 09:19	Solution	#3
Dikkeunit New Member Max Join Date: Sep 2019 Posts: 8 Rep Power: 7	Hey, sorry for not responding, it has slipped my mind that I had opened this thread. I have found the problem, which was that the server used more cores than it physically had. This came to mind when we installed a new version of openMPI, which said we were using more cores than were available! We always assumed also the virtual cores were used by openFOAM, but this is not the case, apparently. So if someone is also struggling with the speed, check your hardware! Thanks

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May 3, 2021, 02:00		#2
olesen Senior Member Mark Olesen Join Date: Mar 2009 Location: https://olesenm.github.io/ Posts: 1,715 Rep Power: 41	Same hardware, similar compilation? Check the single core speeds, next check your mpi. I have heard of slowdowns with particular versions of intel-mpi (I think the latest is good), but I don't know any real details.