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-   -   Multi domain performance penalty???? (http://www.cfd-online.com/Forums/cfx/24114-multi-domain-performance-penalty.html)

Stu June 13, 2007 20:59

Multi domain performance penalty????
 
Can someone tell me if there is a performance penalty when using multiple domains in a sim. Example, I have a large tank, that I have meshed using icem and cfx-mesh. CFX-mesh for the more complex inlet pipes and Icem for the bulk of the rest of the tank. I join the domains together in cfx-pre and all works well.

Neglecting any difference in nodes/elements/tets/hexes, would the solution take longer to solve because it is using 2 doamins, or would it be faster if I did the entire mesh using 1 domain.

Thanks Stu


Joe June 14, 2007 05:43

Re: Multi domain performance penalty????
 
In the problems I've solved I've noticed little to no penalty. These were simple linear geometries with a domain interface in the middle.

Gert-Jan June 14, 2007 18:41

Re: Multi domain performance penalty????
 
The GGI's will deliver a small penalty.

For parallel processing the penalty can be larger. CFX has the drawback that each partition needs at least a part of each domain. So when you have 10 small parts and 1 large part and 3 processors, these 10 small parts are partitioned over the 3 processors as well as the large parts. Even if the 10 small parts would fit on 1 processor.

Gert-Jan

Glenn Horrocks June 14, 2007 18:46

Re: Multi domain performance penalty????
 
Hi,

Whether multiple domains decreases efficiency is problem dependant. The issues are:

Increased efficiency due to: 1) Possibility of improved mesh quality and sizing compared to single domain

Decreased efficiency due to: 1) In parallel, partitioning is done on a domain by domain basis (by default) so there the partition interface area increases. 2) There is an overhead in interfaces. 1 to 1 interfaces have almost no overhead but GGI interfaces have a small overhead.

The balance of these issues determines the effect of the interfaces.

Glenn Horrocks

johnny June 14, 2007 22:36

Re: Multi domain performance penalty????
 
By default, CFX runs in "Independent Partitioning" which behaves as Gert-Jan describes. However, you can run "Coupled Partitioning" and then the partitions do not have this restriction.

Gert-Jan June 16, 2007 13:30

Re: Multi domain performance penalty????
 
Hmmmm, learning every day. Since when does this option exists?

Gert-Jan

johnny June 18, 2007 05:46

Re: Multi domain performance penalty????
 
I think it has been an option for a long time. Definitely it was there in 10.0.

Gert-Jan June 18, 2007 07:32

Re: Multi domain performance penalty????
 
I started with CFX 5.3. It was not present there. Hard to keep up all the new features.......

Gert-Jan

Glenn Horrocks June 18, 2007 18:57

Re: Multi domain performance penalty????
 
Hi,

Yes, it has been there for a while. I have played with it a long time ago for my simulations with a few GGIs in the hope it increased the simulation speed but it actually made it marginally worse. Not sure why.

I would be interested to hear if it works better now, or if it is an improvement for some simulations and not for others.

Glenn Horrocks


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