Re: [Starpu-devel] [daxpy with StarPU-MPI]

[Samuel Thibault <samuel.thibault@inria.fr>]

Hello,

Maxim Abalenkov, le mar. 16 oct. 2018 16:25:18 +0100, a ecrit:
> I came up with an alternative:
> 
> starpu_mpi_scatter_detached(hx, NT, ROOT, MPI_COMM_WORLD, 0, 0, 0, 0);
> 
> But I am not sure it is correct.

The 4 nul parameters were missing in the documentation indeed.

> b) Is it possible to use vector filters to automatically partition the data 
> in
> StarPU-MPI, similarly to the normal StarPU?

It seems we haven't tested that case, but it should work, yes.

> Below is a code snippet I use in
> the normal StarPU, but I’m not certain it can be adapted to StarPU-MPI, due 
> to
> the need of explicit registration of vector segments with MPI.

I guess you just need, after calling starpu_data_partition, to register
each subdata to MPI with starpu_mpi_data_register, which a different tag
for each piece.

> c) Finally, what is the recommended way of initialising the vector data in 
> the
> "scatter—gather" example? So far, I am initialising each vector segment on 
> the
> root processor. Is there a better way, e.g. initialising the entire vectors
> before splitting them into segments and registering with StarPU and MPI?

You can initialize the whole vector in just one task, yes, it will be
more efficient, but it will be less parallel. You can also just let MPI
nodes initialize their own piece, which will allow for yet more parallelism.

Samuel