Abstract:
Gadget-2 is a production parallel code for cosmological N-body and hydrodynamic
simulations. Versions of this code featured in the Millennium Simulation,
which is the largest simulated model of the universe. Gadget-2 has
been parallelized for distributed memory platforms using the MPI standard.
In this thesis | we analyzed Gadget-2 with a view to understanding what
high-level SPMD communication abstractions might be developed to replace
the intricate use of MPI in such irregular applications and do so without
compromising the e ciency. Our analysis revealed that the use of low-level
MPI primitives bundled with the computation code makes Gadget-2 di cult
to understand and probably hard to maintain. In addition, we found out
that the original Gadget-2 code contains a small handful of complex and
recurring-patterns of message passing. We also noted that these complex
patterns can be reorganized into a higher level communication library with
some modi cations to the Gadget-2 code. This thesis presents the implementation
and evaluation of one such message passing pattern (or schedule)
that we term Collective Asynchronous Remote Invocation (CARI). As the
name suggests, CARI is a collective variant of Remote Method Invocation
(RMI), which is an attractive, high-level, and established paradigm in distributed
systems programming. The CARI API might be implemented in
several ways | we implement and evaluate two versions of this API on a
compute cluster. The performance evaluation reveals that CARI versions of
the Gadget-2 code perform as good as the original Gadget-2 code but the
level of abstraction is raised considerably. In fact one of the implementations
has geared towards scalability on larger number of cores which performs the
best when the problem size reaches its scalability limits.
