Note some optimizations that could be useful

mpi/src/mpi/starpu_mpi_mpi.c

@@ -255,6 +255,7 @@ void _starpu_mpi_submit_ready_request(void *arg)
 
 				_STARPU_MPI_DEBUG(3, "Calling data_acquire_cb on starpu_mpi_copy_cb..\n");
 				STARPU_PTHREAD_MUTEX_UNLOCK(&progress_mutex);
+				// FIXME: when buffer == NULL, do not hardcode acquiring on early_data_handle->buffer_node, to just acquire where the data happens to have been stored by MPI
 				starpu_data_acquire_on_node_cb(early_data_handle->handle,early_data_handle->buffer_node,STARPU_R,_starpu_mpi_early_data_cb,(void*) cb_args);
 				STARPU_PTHREAD_MUTEX_LOCK(&progress_mutex);
 			}