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Subject: Re: [OMPI devel] Question about barrier()
From: Jeff Squyres (jsquyres_at_[hidden])
Date: 2010-11-02 11:54:43

On Nov 2, 2010, at 10:11 AM, <ananda.mudar_at_[hidden]> <ananda.mudar_at_[hidden]> wrote:

> Yes, I am calling MPI_Init_thread() with MPI_THREAD_MULTIPLE. And I have enabled thread and mpi_threads while configuring OpenMPI. BTW, I am using OpenMPI 1.4.2.
> It will be helpful to know if this is a design constraint or some implementation defect.

When you use MPI_THREAD_MULTIPLE, we're activating locks that aren't necessary when you're MPI_THREAD_SINGLE. These locks therefore cost overhead time that you don't normally see (and potentially system time as opposed to user time). To date, we haven't spent a huge amount of time optimizing the THREAD_MULTIPLE code paths. There's a number of efforts going on that may help with this, but it will take some time.

Jeff Squyres
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