communication between partitions in parallel

Numerical methods and mathematical models of Elmer
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lionel
Posts: 27
Joined: 26 Jan 2010, 12:32

communication between partitions in parallel

Post by lionel »

Hi Elmer,

There are parallel issues for me today...
I'm simulating in parallel an ice sheet bounded vertically between two surfaces. From any partition, I need to know the coordinates of these both surfaces, but I don't know any way to allow a communication between two partitions, except on the boundaries.
So is there a way to communicate between two partitions, or to access an information inside a partition from any other partition ?

Cheers
Lionel
lionel
Posts: 27
Joined: 26 Jan 2010, 12:32

Re: communication between partitions in parallel

Post by lionel »

Hi again,

I found some routines which might be able to resolve my problem. There are some functions called MPI_RECV and MPI_SEND and also MPI_BSEND and others...
I don't really understand the difference between these functions and I would need some lights ? Would you have some documentation somewhere about that ?

Regards
Lionel
raback
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Re: communication between partitions in parallel

Post by raback »

Hi Lionel

These are standard MPI commands which are not Elmer specific. For MPI guides see for example
http://www.mcs.anl.gov/research/project ... rning.html

The parallel implementation is quite another thing and I don't have much insight in there. Perhaps you could open a little bit your problem since having non-local MPI communication may mean trouble for the scaling.

-Peter
lionel
Posts: 27
Joined: 26 Jan 2010, 12:32

Re: communication between partitions in parallel

Post by lionel »

Hi Raback,

Thanks for the web page.
I'm starting to learn about MPI programming and the "MPI User's Guide in Fortran" seems to be newbie friendly.

Cheers
Lionel
lionel
Posts: 27
Joined: 26 Jan 2010, 12:32

Re: communication between partitions in parallel

Post by lionel »

Hi,

Another question about communication between partitions.
Globally speaking, I would like to know the effect of these commands on the computational cost. Did you observe some non negligible lost of efficiency or it doesn't matters ?

Cheers
Lionel
tzwinger
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Re: communication between partitions in parallel

Post by tzwinger »

Hi Lionel,
in parallel computing communication (i.e., utilizing the MPI calls) is the main cause of performance limits. The less your parallel tasks have to talk to each other, the more they can spend on doing the number-crunching. Especially if you use blocking communication (when often CPU's are idle waiting for the others to be ready to communicate).

Cheers,

Thomas
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