MPI-4.0 section 11.2.1, page 488 lines 32-33 and 47-48: "When using the World Model, MPI is initialized by calling either MPI_INIT or MPI_INIT_THREAD." and "In the World Model, an MPI program must contain exactly one call to an MPI initialization routine: MPI_INIT or MPI_INIT_THREAD." Mix-and-match. Best wishes, Dan. -----Original Message----- From: mpiwg-hybridpm <[email protected]> On Behalf Of Michael Knobloch via mpiwg-hybridpm Sent: Tuesday, August 1, 2023 11:39 AM To: [email protected] Cc: Michael Knobloch <[email protected]> Subject: Re: [mpiwg-hybridpm] Can MPI processes request different threading levels? I'm not even sure it fully answers the question. This statement says that MPI processes can request different requirements in MPI_Init_thread, but it doesn't say whether all processes must be initialized with a call to the same routine or if some can be initialized with MPI_Init (and assume MPI_THREAD_SINGLE?) and some with MPI_Init_thread, which was the original question. -Michael On 01.08.23 12:24, Joseph Schuchart via mpiwg-hybridpm wrote:

Funny that this is inside an advice to implementors (which users like Joachim are not expected to read) when it really should be part of the normative text.

Cheers Joseph

On 8/1/23 11:09, Jeff Hammond via mpiwg-hybridpm wrote:

...

It is addressed here (in the text for MPI_INIT_THREAD):

Advice to implementors. If provided is not MPI_THREAD_SINGLE then the MPI library should not invoke C or Fortran library calls that are not thread safe, e.g., in an environment where malloc is not thread safe, then malloc should not be used by the MPI library.

Some implementors may want to use different MPI libraries for different levels of thread support. They can do so using dynamic linking and selecting which library will be linked when MPI_INIT_THREAD is invoked. If this is not possible, then optimizations for lower levels of thread support will occur only when the level of thread support required is specified at link time.

*Note that required need not be the same value on all processes of MPI_COMM_WORLD.* (End of advice to implementors.)

Jeff

On Tue, Aug 1, 2023 at 11:47 AM Joachim Jenke via mpiwg-hybridpm <[email protected]> wrote:

...

Hello,

I'm not sure whether this is the right group to ask, but it is related to hybrid execution :)

Must all MPI processes collectively call MPI_Init or MPI_Init_thread - or can some processes call one and other processes call the other

function?

...

Also, can the processes request different thread-support levels?

Our use case is MPMD execution, where some processes run

multi-threaded

...

and other single-threaded.

Thanks, Joachim

-- Dr. rer. nat. Joachim Jenke

IT Center Group: High Performance Computing Division: Computational Science and Engineering RWTH Aachen University Seffenter Weg 23 D 52074 Aachen (Germany) Tel: +49 241 80- 24765 Fax: +49 241 80-624765 [email protected] www.itc.rwth-aachen.de <http://www.itc.rwth-aachen.de> _______________________________________________ mpiwg-hybridpm mailing list [email protected] https://lists.mpi-forum.org/mailman/listinfo/mpiwg-hybridpm

-- Jeff Hammond [email protected] http://jeffhammond.github.io/

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