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Subject: Re: [OMPI users] BTL layer
From: Gabriele Fatigati (g.fatigati_at_[hidden])
Date: 2010-09-22 13:53:06


Thanks Jeff,

and.. what about RDMA? It works only with point-to-point or also with
collectives?

2010/9/22 Jeff Squyres <jsquyres_at_[hidden]>

> On Sep 22, 2010, at 3:46 AM, Gabriele Fatigati wrote:
>
> > i'm tuning collectives of OpenMPI 1.4.2 with OTPO. I have a little
> question about BTL. This layer is involves just in point-to-point
> communication or also in collectives routines?
> >
> > Because i've noted that changing some blt parameters like
> btl_sm_eager_limit and doing one collective routine, performances can have
> very different behaviour.
>
> The BTLs are dumb byte transport layers -- they have no idea of any MPI
> semantics.
>
> But that being said, they act as the lowest layers for the MPI
> point-to-point functions (MPI_SEND and the like). They may *also* act as
> the lowest layers for all of the collective functions. Some collective
> algorithms call MPI_SEND to do their individual sends, for example. Others
> may invoke BTL send/receive functions directly. Others don't use the BTLs
> at all.
>
> --
> Jeff Squyres
> jsquyres_at_[hidden]
> For corporate legal information go to:
> http://www.cisco.com/web/about/doing_business/legal/cri/
>
>
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-- 
Ing. Gabriele Fatigati
Parallel programmer
CINECA Systems & Tecnologies Department
Supercomputing Group
Via Magnanelli 6/3, Casalecchio di Reno (BO) Italy
www.cineca.it                    Tel:   +39 051 6171722
g.fatigati [AT] cineca.it