Re: [Starpu-devel] Question about MPI usage

[Xavier Lacoste <xl64100@gmail.com>]

Le 25 févr. 2014 à 15:07, Samuel Thibault <samuel.thibault@ens-lyon.org> a 
écrit :

> Xavier Lacoste, le Tue 25 Feb 2014 11:52:21 +0100, a écrit :
>> Thanks, this is due to a read only array that I only register on the node 
>> which will execute the task.
> 
> And no other task will need the array?

This data is only defined on proc P because only task executed on proc P can 
use it, but there can be multiple task.
Finally, I registered one data_handle per process and which pointed to NULL 
buffer when non local, and I choosed the good one using 
starpu_get_data_rank() on the written data (which decides on which proc the 
task will be executed) .

Thanks

XL.

> 
>> Do I need to register it on every node ?
> 
> No, only on nodes which will actually pass it to starpu_mpi_task_insert.
> 
> You can also pass NULL to starpu_mpi_task_insert, it will just return
> EINVAL.
> 
>> Is there an option to tell StarPU that this buffer is already on the
>> node that will execute the kernel ?
> 
> Well, you at least need to specify an MPI rank for the data, so that
> StarPU knows it is here and doesn't have to transfer anything.
> 
> Samuel