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Re: [Starpu-devel] StarPU on multiple communicator


Chronologique Discussions 
  • From: Nathalie Furmento <nathalie.furmento@labri.fr>
  • To: Xavier Lacoste <xavier.lacoste@inria.fr>
  • Cc: Mathieu Faverge <Mathieu.Faverge@inria.fr>, starpu-devel@lists.gforge.inria.fr
  • Subject: Re: [Starpu-devel] StarPU on multiple communicator
  • Date: Mon, 26 Jan 2015 11:35:21 +0100
  • List-archive: <http://lists.gforge.inria.fr/pipermail/starpu-devel/>
  • List-id: "Developers list. For discussion of new features, code changes, etc." <starpu-devel.lists.gforge.inria.fr>

Hello,

I tried a simple application which splits in 2 communicators a group of 4 MPI
processes,
and a communication is made between the rank 0 and the rank 1 of each new sub
communicator.

This works fine with the branch 1.1 of StarPU. However it fails with the
trunk version of
StarPU. Its new communication engine assumes MPI_COMM_WORLD to be the
communicator for all
communications. I am going to have a look at how it can be fixed. I will keep
you informed.

Cheers,

Nathalie

On Jan 23, 16:40, Xavier Lacoste wrote:
> Hello,
>
> I am using PaStiX in Jorek (A Tokamak simulation code).
>
> Jorek uses sub-communicators to factorize different matrices on different
> communicators (i.e. P0 and P1 factorize mat1 while P2 and P3 factorize
> mat2). The two matrices have exactly the same shape, so the same shape
> block columns (my data unit in starpu), identified with the same tags, but
> these data are in fact different as they belong to different matrices (mat1
> and mat2).
>
> As far as I understand this cannot work in StarPU today ( I saw Nathalie
> who agrees with me on that ;) ).
>
> P0 and P2 (resp. P1 and P3) will register their data with exactly the same
> TAG. Thus we have two different data with the same TAG which could be a
> problem.
>
> An other issue is that the rank of the data is set using the
> sub-communicator rank which may not be what is expected by StarPU.
>
> All this results in StarPU hanging in a deadlock, certainly waiting for
> communications...
>
> I hope I am not too confusing in my explanations.
>
> I'll try a hack in my code to fix that: use global rank when registering
> data and retrieve the number of communicators (here my communicators have
> the same size hopefully) and add an offset to the TAGS.
>
> I think supporting communicator in StarPU would be a great feature.
>
> Regards,
>
> XL.
>
>
> ----------------------------------------
> Xavier Lacoste
> xavier.lacoste@inria.fr
> INRIA Bordeaux Sud-Ouest
> 200, avenue de la Vieille Tour
> 33405 Talence Cedex
> Tél : +33 (0)5 24 57 40 69
>
>
>
>
>
>
>
>

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Dr Nathalie Furmento Ingénieur de recherche CNRS
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