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Understanding hardware & parallel processing requirements

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Old   May 3, 2018, 17:45
Default Understanding hardware & parallel processing requirements
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YK
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Hello, forum!

I am a grad student. For my thesis, I was given access to below set of Hardware & Software.
Windows Server 2012 R2 Standard
Intel (R) Xeon (R) CPU E5-2650 v3 @2.30GHz (2 Processors)
128GB RAM & 64 bit OS
Sockets-2, Cores-20 & Logical Processors-40

ANSYS 19.0- Workbench, Fluent, Mechanical & System Coupling with following licenses ANSYS Academic Research Mechanical & CFD, ANSYS Academic Research HPC.

In ANSYS license preferences there's statement ***The maximum number of HPC pack licenses that can be requested per user for a solve is 14**
Being naive I have been using these resources without even understanding the complete potential, for instance, by changing processor number for the parallel in the Fluent launcher or Mechanical settings.

In a particular case:
With 10 processors on Mechanical & 24 on Fluent, the transient FSI simulation was working fine. But the use of implicit update in Fluent threw an error "mpirun.exe has stopped working".

However, it was working well if I set 2 or 4 processors on each.

I have not found any solution to this yet.
This error pushed me off bad to get a better understanding of parallel processing settings.

I am requesting this forum to help me understand the capabilities of these resources. How many processors can I possibly set up for Fluent and Mechanical for 10K-1M elements/nodes in each mesh? Do I need an MPI for this server? Is the number of processors related to licenses available?

I would really appreciate if anyone can help me get these basics right.

Thank you.

YK
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Old   May 23, 2018, 09:42
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You error so far seems pretty generic. mpirun.exe has stopped running means one of the parallel processes stopped, which doesn't really give much information.

You always need an mpi for parallel simulations.

The HPC pack is a non-linear scaling license which starts at base 8 and scales in powers of 4. 1 HPC Pack lets you run on 8 processes. 2 HPC packs will let you run on 32, 3 Packs on 128, etc. 14 packs is a lot, 2 billion processes simultaneously. So you don't have a licensing problem.

I would go into the bios and disable hyper threading; it causes too many problems without any benefit in a computing job. 1 E5-2650 has 10 physical cores (20 hyperthreaded). So 2x E5-2650's you have 20 physical cores (40 hyperthreaded). When you specify 10+24 processes, that is more than the 20 physical cores so some of these processes end up on the hyper-threaded ones. So you're not getting any speed benefit past a total of 20 processes. But even if you specify a number less than 20, you cannot control and ensure that the simulation is running on only the non-virtual cores. So it's best (especially when you have these problems) to disable hyperthreading entirely. Do this and see if you can run on 20 processes stably.
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Old   May 24, 2018, 13:29
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Just for info, the below message has nothing to do with how many HPC license one actually have. I think it just means that, given you could afford 15 HPC packs, you still could only use up to 14 for a solve.

***The maximum number of HPC pack licenses that can be requested per user for a solve is 14
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Old   May 24, 2018, 13:34
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ha, ha, ha, I did not think of it.


Well then it would be helpful if the license configuration is posted. Btw, if there aren't enough licenses, the processes will not start and you won't get very far and you would never be able to run anything. Hence, it should be quite obvious... So I assume there's not a licensing problem.
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