  MPI is the most widely used data transfer and communication model in High
Performance Computing. The latest version of the standard, MPI-3, allows
skilled programmers to exploit all hardware capabilities of the latest and
future supercomputing systems. The revised asynchronous remote-memory-access
model in combination with the shared-memory window extension, in particular,
allow writing code that hides communication latencies and optimizes
communication paths according to the locality of data origin and destination.
The latter is particularly important for today's multi- and many-core systems.
However, writing such efficient code is highly complex and error-prone. In this
paper we evaluate a recent remote-memory-access model, namely DART-MPI. This
model claims to hide the aforementioned complexities from the programmer, but
deliver locality-aware remote-memory-access semantics which outperforms MPI-3
one-sided communication primitives on multi-core systems. Conceptually, the
DART-MPI interface is simple; at the same time it takes care of the
complexities of the underlying MPI-3 and system topology. This makes DART-MPI
an interesting candidate for porting legacy applications. We evaluate these
claims using a realistic scientific application, specifically a
finite-difference stencil code which solves the heat diffusion equation, on a
large-scale Cray XC40 installation.
