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Subject: Re: [OMPI users] Implementation of TCP v/s OpenIB (Eager and Rendezvous) protocols
From: Siddhartha Jana (siddharthajana24_at_[hidden])
Date: 2014-02-01 11:46:49


Thanks for the reply Jeff. This is directional.
On 01-Feb-2014 7:51 am, "Jeff Squyres (jsquyres)" <jsquyres_at_[hidden]>
wrote:

> On Jan 31, 2014, at 2:49 AM, Siddhartha Jana <siddharthajana24_at_[hidden]>
> wrote:
>
> > Sorry for the typo:
> > ** I was hoping to understand the impact of OpenMPI's implementation of
> these protocols using traditional TCP.
> >
> > This is the paper I was referring to:
> > Woodall, et al., "High Performance RDMA Protocols in HPC".
> >
> >
> > On 31 January 2014 00:43, Siddhartha Jana <siddharthajana24_at_[hidden]>
> wrote:
> > Good evening
> > Is there any documentation describing the difference in MPI-level
> implementation of the eager and rendezvous protocols in OpenIB BTL versus
> TCP BTL ?
>
> Unfortunately, there is not, sorry. Just the code. :-\
>
> > I am only aware of the following paper. While this presents an excellent
> overview of how RDMA capabilities of modern interconnects can be leveraged
> for implementing these protocols, I was hoping to understand how OpenMPI
> implications of handling these protocols using traditional TCP.
>
> The easiest way to think about it is that the TCP BTL could well be
> implemented with just the "send" method (and no "get" or "put" methods).
>
> That being said, the TCP BTL does emulate the "put" method (meaning:
> there's obviously no hardware support for a direct data placement using a
> general socket in TCP like there is with OpenFabrics-style RDMA) simply
> because it allows us to be slightly more efficient on the receiver (IIRC;
> it's been a loooong time since I've looked at that code).
>
> --
> Jeff Squyres
> jsquyres_at_[hidden]
> For corporate legal information go to:
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