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Subject: Re: [OMPI users] OpenMP + OMPI
From: George Bosilca (bosilca_at_[hidden])
Date: 2008-01-12 22:20:29


Both cases should work just fine. In fact as long as there is only one
execution flow using MPI functions, the user will not face any problems.

In a non-threaded build, there is no real progress outside the MPI
calls. Here by real progress I understand MPI request progress,
something that is visible from the user level (such as request
completion).

If a blocking send is used, and the length of the data is under the
eager limit, the message will stay in the network until the receiver
access some MPI function. However, in this case the sender is free to
continue its execution. In the case where the length exceed the eager
size, the sender will be blocked until the corresponding receive is
posted (and then the rendez-vous protocol completed and data
transmitted).

   george.

On Jan 12, 2008, at 9:16 PM, Brock Palen wrote:

> Hey guys,
> I know that threading is very immature (or broken) in the 1.2
> series, But what happens if a user wants to use a threaded BLAS
> (GOTO) library with their MPI code and never has OpenMP/pthreads
> parallel regions with MPI calls? Would this work?
>
> What about using OpenMP in their code but again all MPI calls happen
> outside parallel regions. How would a process who is behind in
> execution handle a incoming message when it has not yet hit outside
> the threaded region ware the MPI_Recv() is called? Would the library
> just hold on to it (if below the eager limit) and wait until someone
> calls the Recv that matches the message?
>
>
> Brock Palen
> Center for Advanced Computing
> brockp_at_[hidden]
> (734)936-1985
>
>
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> users mailing list
> users_at_[hidden]
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