Relax the constraint on the MPI tags when using StarPU 1.2

Each tiles needs a unique tag identifier for the communication with StarPU. By default, the first 8 bits are dedicated to the descriptors, and the remaining bits to the tiles within the descriptor.

With StarPU 1.2, we should be able to always keep the 32bits for the tags even with MPI implementation that provides a lower tag upper bound. The solution to this problem will be fixed, when StarPU will provide a standard way to know its own upper bound for the tags.

@furmento to add myself as a participant

assigned to @furmento

should we define

STARPU_MPI_TAG_UB to be MPI_TAG_UB when using the new communication engine (i.e the one which sends all messages with the same tag)

and

STARPU_MPI_TAG_UB to some lower value (i would not know which value) with the old communication engine?

@thibault

No, it's with the old communication engine that we need to report what MPI_Attr_get(MPI_TAG_UB) provides.

With the new communication engine we should report what we support, which is currently INT_MAX/2 (since the tags we use in starpu-mpi are signed ints)

mentioned in issue #55 (closed)

StarPU now provides a function starpu_mpi_comm_get_attr() to get the value of an attribute for a given key. The key STARPU_MPI_TAG_UB will retrieve the upper bound for tag value.

• For starpu 1.2, the upper bound is INT_MAX
• For the trunk, the upper bound is INT64_MAX

closed

Well, starpu now provides the function but now we need to make chameleon use it in RUNTIME_desc_create :)

reopened

mentioned in merge request !88 (merged)

closed via commit 5ea33ef2

closed via commit 0e793439

closed via merge request !88 (merged)