Re: [Starpu-devel] Using STARPU_COMMUTE with starpu_mpi_task_build()

[Xavier Lacoste <xl64100@gmail.com>]

Le 28 févr. 2014 à 17:58, Samuel Thibault <samuel.thibault@ens-lyon.org> a écrit :

Xavier Lacoste, le Wed 26 Feb 2014 16:56:05 +0100, a écrit :

Le 26 févr. 2014 à 16:30, Samuel Thibault <samuel.thibault@ens-lyon.org> a écrit :

Xavier Lacoste, le Wed 26 Feb 2014 15:43:26 +0100, a écrit :

I tried to use STARPU_COMMUTE with MPI but the option gives an error when building MPI task.
Indeed it does not appear in the test "if (arg_type==STARPU_R || arg_type==STARPU_W || arg_type==STARPU_RW || arg_type==STARPU_SCRATCH || arg_type==STARPU_REDUX" in starpu_mpi_task_insert.c
Is this the only thing missing or is it more complicated ?

On the top of my head I think it's a matter of testing against
arg_type & ~STARPU_COMMUTE to get it working at least. Getting it
optimized is probably another question, could you show us your use case?

I have several task preforming a GEMM updating a data that can be executed in parallel.
In shared memory mode I just used starpu_data_set_sequential_consistency_flag() and listed all my dependencies, but as it was more complicated to get the list of tasks in distributed, I tried STARPU_COMMUTE.

So, in my algorithm, I have several GEMM tasks unlocking a GETRF+TRSM unlocking an other list of GEMMs etc.

Ok, and are all the GEMMs happening on the same MPI node?

Yes all GEMMs applying on one column block are performed on the MPI node that owns the column block (it's the only "write access" data of the GEMM task).

Thinking about it, I tend to think that we don't want to optimize the
case where it would not be on the same MPI node, i.e. simply ignore the
STARPU_COMMUTE flag for all the MPI stuff (but of course keep it for the
actual task insertion, to get the commute effect inside MPI nodes.

Is that what you wanted to know ?

Yes :)

Samuel

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