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Subject: Re: [OMPI devel] sm BTL question: frag alloc
From: George Bosilca (bosilca_at_[hidden])
Date: 2009-02-17 20:37:17


Eugene,

It appears this is a sm BTL problem. The prepare_src function can be
called with any size. The BTL should check the size against the eager
and return a descriptor that match the size requested.

   george.

On Feb 17, 2009, at 20:14 , Eugene Loh wrote:

> (Rich: same question as I asked you in private e-mail.)
>
> Should the first fragment of a message be an eager fragment even
> when the message is long and a rendezvous protocol is employed?
>
> So far as I can tell, a long MPI_Send starts like this:
>
> MPI_Send()
> mca_pml_ob1_send()
> mca_pml_ob1_send_request_start()
> mca_pml_ob1_send_request_start_btl()
>
> http://svn.open-mpi.org/source/xref/ompi_1.3/ompi/mca/pml/ob1/pml_ob1_sendreq.h?r=20298#340
> Here we see (e.g., line 368) that if we're over the eager limit, we
> try to send the first fragment with "eager" size. Then,
>
> mca_pml_ob1_send_request_start_rndv()
> mca_bml_base_prepare_src()
> mca_btl_sm_prepare_src()
>
> But if we look at http://svn.open-mpi.org/source/xref/ompi_1.3/ompi/mca/btl/sm/btl_sm.c#mca_btl_sm_prepare_src
> it appears to alloc a "MAX" (not EAGER) fragment. Is this a
> "bug"? Should the BTL be allocating an EAGER fragment instead? Or,
> could this function possibly be called with size>eager? Or, should
> the BTL alloc a MAX *or* EAGER fragment depending on what size is
> requested?
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