[Starpu-devel] Why starpu_mpi_barrier waits for all taks ?

[Philippe SWARTVAGHER <philippe.swartvagher@inria.fr>]

Hello,

I'm trying to fix a bug reported by Nathalie: 
mpi/tests/sendrecv_gemm_bench isn't working with MPI backend because of 
calls to starpu_mpi_barrier().

Indeed, the MPI version of starpu_mpi_barrier() calls 
starpu_task_wait_for_all(). Hence the deadlock in the test:

- starpu_pause()

- task submission

- starpu_mpi_barrier() <-- cannot finish since starpu_task_wait_for_all 
is blocking

- starpu_release()


Why starpu_mpi_barrier waits for all tasks ? Is it because with MPI we 
cannot have concurrent barriers ?

Could we consider creating a function starpu_mpi_barrier_unsafe(), 
calling directly MPI_Barrier ?

--
Philippe SWARTVAGHER

Doctorant
Équipe TADaaM, Inria Bordeaux Sud-Ouest