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[snappyHexMesh] Decomposed sHM runs slower than on single thread |
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February 19, 2020, 11:31 |
Decomposed sHM runs slower than on single thread
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#1 |
New Member
Tom
Join Date: Nov 2019
Posts: 2
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Hello,
I'm meshing a more-or-less cylindrical geometry (screenshot attached below, flow through a duct) with sHM. I used a simple (2 2 2) decomposition in decomposeParDict ((2 2 1) for 4 threads). I'm running the case in this order: blockMesh surfaceFeatures decomposePar mpirun -np 8 snappyHexMesh -overwrite -parallel However, the more cores I use, the slower snappyHexMesh runs. Just adding new boundary patches takes too long to let it finish the job. I'm using Ubuntu 16.04 LTS on Windows 10. The processor is a 4-core (8 threads) i7-7700HQ. When using 8 threads, the CPU usage jumps to 100%, while with 4 it stays at about 60%, so the decomposition itself seems to be working. What may be the cause of such behaviour? I'll gladly provide more details as needed. |
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February 19, 2020, 17:29 |
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#2 |
Senior Member
Herpes Free Engineer
Join Date: Sep 2019
Location: The Home Under The Ground with the Lost Boys
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how many cells per processor?
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February 20, 2020, 13:30 |
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#3 |
Senior Member
Join Date: Mar 2014
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This is perfectly normal because your processor has 4 real cores so your max parallelization limit is 4!
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February 23, 2020, 07:31 |
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#4 | |
New Member
Tom
Join Date: Nov 2019
Posts: 2
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~3000 after blockMesh, limit in sHM set to 0.8*10^6.
Quote:
However, any decomposition seems to be much slower than using just a single core. I've tried using every number of processors between 2 and 8, yet the performance always dropped. |
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