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From: Jeff Squyres (jsquyres_at_[hidden])
Date: 2007-07-12 10:28:43

At the moment, I believe that this should be safe in Open MPI (read a
buffer that is currently being sent). No claims about the future,
though. :-)

On Jul 12, 2007, at 1:07 AM, Isaac Huang wrote:

> It's prohibited by the standard to read send buffer before a send
> operation completes, and I understand the theoretical rationale behind
> it.
> I'm currently layering a protocol stack on top of MPI, and this
> protocol allows a buffer to be read by multiple peers concurrently.
> Thus for strict conformance I can either serialize read access to such
> buffers or just make memory copies - neither approach is optimal. I'm
> wondering that whether there is any practical exploitation of this
> restriction - Is there an Open MPI BTL driver (or whatever it is
> called in the Open MPI architecture) that really unmaps pages that are
> totally contained inside the communication buffer from the application
> address space while doing DMA?
> If the answer is none or very rare, then I'll perhaps just dismiss it
> as a red herring and big headache can be avoided.
> Thanks,
> Isaac
> --
> Regards, Isaac
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Jeff Squyres
Cisco Systems