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Subject: Re: [OMPI users] configure: mpi-threads disabled by default
From: Mark Dixon (m.c.dixon_at_[hidden])
Date: 2011-05-05 06:55:51


On Wed, 4 May 2011, Eugene Loh wrote:

> Depending on what version you use, the option has been renamed
> --enable-mpi-thread-multiple.
>
> Anyhow, there is widespread concern whether the support is robust. The
> support is known to be limited and the performance poor.

Thanks :)

I absolutely see why support for MPI_THREAD_MULTIPLE is a configure option
(not at all related to the fact I'm on a platform where my best
interconnect gets disabled if you ask for it).

However, do the same concerns apply to MPI_THREAD_FUNNELED and
MPI_THREAD_SERIALIZED? They are disabled by default too and they look
difficult to enable without enabling some other functionality.

Details:

Jeff said (on this list, Tue, 14 Dec 2010 22:52:40) that, in OpenMPI,
there's no difference between MPI_THREAD_SINGLE and MPI_THREAD_FUNNELED.
Yet, with the default configure options, MPI_Init_thread will always
return MPI_THREAD_SINGLE.

* Release 1.4.3 - MPI_THREAD_(FUNNELED|SERIALIZED) are only available if
you specify "--mpi-threads". Codes that sensibly negotiate their thread
level automatically start using MPI_THREAD_MULTIPLE and my interconnect
(openib) is disabled.

* Release 1.5.3 - MPI_THREAD_(FUNNELED|SERIALIZED) are only available if
you specify "--mpi-threads" (same problems as with 1.4.3), or enable
asynchronous communication progress (whatever that is - but it sounds
scary) with "--enable-progress-threads"

Things do look different again in trunk, but seem to require you to at
least ask for "--enable-opal-multi-threads".

Are we supposed to be able to use MPI_THREAD_FUNNELED by default or not?

Best wishes,

Mark

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Mark Dixon                       Email    : m.c.dixon_at_[hidden]
HPC/Grid Systems Support         Tel (int): 35429
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