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-   -   Minimum number of nodes to run CFX in parallel (http://www.cfd-online.com/Forums/cfx/21148-minimum-number-nodes-run-cfx-parallel.html)

Rui April 6, 2005 14:48

Minimum number of nodes to run CFX in parallel
 
Hi,

The CFX documentation (Solver Modelling, Using the Solver in Parallel, page 394) says that performance increase will only be noticeable if the number of nodes per partition is greater than 30,000 (for tet meshes) or greater than 75,000 (for hex meshes).

I'm doing transient free surface problems, for which I need quite small time-steps to achieve convergence. As a consequence of that, I have to use meshes with just a few thousand number of nodes. Even with these meshes, my simulations take some days (sometimes 1-2 weeks) to complete.

I allways run the simulations in only one PC with only one processor (Pentium 4). Do you really think that if I run a simulation, with a mesh made up of 2-3 thousand nodes, in parallel with 2, 3 or 4 PCs, I will not notice any performance increase as mentioned by the documentation?

Thank you for your help.

Regards,

Rui

Glenn Horrocks April 6, 2005 18:27

Re: Minimum number of nodes to run CFX in parallel
 
Hi,

The only way to be sure is to run it and try. I have got quite useful speedups on small meshes so there is a good chance you will go faster.

Glenn Horrocks

Neale April 7, 2005 20:58

Re: Minimum number of nodes to run CFX in parallel
 
You can try it but it will probably be minimal.

Robin April 11, 2005 20:46

Re: Minimum number of nodes to run CFX in parallel
 
Hi Rui,

Technically, you can run with as many computers as you have nodes, so a mesh comprising of a single hex element can be run on 8 cpu's! However, in practice the inter-process communication time begins to outweight the computation time as your node count drops.

That is not to say you will not see speedup. Generally, parallel efficiency will begin to drop off below 100k nodes and become significantly inefficient below 30k nodes. At 2 to 3 thousand nodes, you might still see some speedup, but probably nowhere near the number of cpu's (i.e. 4 cpu's will not give you a 4x speedup).

Best regards, Robin


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