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Subject: Re: [OMPI users] Documentation of MPI Implementation
From: Hoang-Vu Dang (dang.hvu_at_[hidden])
Date: 2011-08-24 09:14:33


Thanks Jeff,

I know it depends and I want to know exactly what is the dependency and
general complexity analysis.

Is it really no documentation at all ? For example you said "to be replaced
soon", then what is the algorithms that will be used to replace ? Is there
any publication available ? In another words, how do you know they will be
replaced by which algorithm, please teach me !
Cheers,
Vu

On Wed, Aug 24, 2011 at 9:07 PM, Jeff Squyres <jsquyres_at_[hidden]> wrote:

> On Aug 23, 2011, at 3:32 AM, Hoang-Vu Dang wrote:
>
> > Where could I find a detailed documentation about algorithms that has
> been using in Open MPI ?
>
> Unfortunately, you probably won't.
>
> > For example, I would like to answer following questions: how MPI_Algather
> operation is done? what is the complexity in term of the number of data
> send/receive given a number of node involved? what is the data structure
> behind ?. Same as for MPI_Alreduce etc..
>
> All of OMPI's collectives are implemented as plugins under the
> ompi/mca/coll/ tree. There are several different plugins in that tree --
> each one has its own directory (with the exception of "base", which is glue
> code for the whole collective algorithm framework).
>
> You probably want to look in the "tuned" component for OMPI's
> current-generation algorithms (to be replaced soon, but that's what's mostly
> used today). "tuned" has many different algorithm implementations for each
> MPI collective, and uses sophisticated run-time checking to determine which
> to use.
>
> So the answer to your original query -- how is the MPI_Allgather operation
> done? -- is, "it depends" on things like message size, number of peers,
> etc. :-)
>
> --
> 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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