Communication Optimizations for Distributed-Memory X10 Programs

Abstract

Abstract-X10 is a new object-oriented PGAS (Partitioned Global Address Space) programming language with support for distributed asynchronous dynamic parallelism that goes beyond past SPMD message-passing models such as MPI and SPMD PGAS models such as UPC and Co-Array Fortran. The concurrency constructs in X10 make it possible to express complex computation and communication structures with higher productivity than other distributed-memory programming models. However, this productivity often comes at the cost of high performance overhead when the language is used in its full generality. This paper introduces high-level compiler optimizations and transformations to reduce communication and synchronization overheads in distributed-memory implementations of X10 programs. Specifically, we focus on locality optimizations such as scalar replacement and task localization, combined with supporting transformations such as loop distribution, scalar expansion, loop tiling, and loop splitting. We have completed a prototype implementation of these high-level optimizations, and performed a performance evaluation that shows significant improvements in performance, scalability, communication volume and number of tasks. We evaluated the communication optimizations on three platforms: a 128-node BlueGene/P cluster, a 32-node Nehalem cluster, and a 16-node Power7 cluster. On the BlueGene/P cluster, we observed a maximum performance improvement of 31.46× relative to the unoptimized case (for the MolDyn benchmark). On the Nehalem cluster, we observed a maximum performance improvement of 3.01× (for the NQueens benchmark) and on the Power7 cluster, we observed a maximum performance improvement of 2.73× (for the MolDyn benchmark). In addition, there was no case in which the optimized code was slower than the unoptimized case. We also believe that the optimizations presented in this paper will be necessary for any high-productivity PGAS language based on modern object-oriented principles, that is designed for execution on future Extreme Scale systems that place a high premium on locality improvement for performance and energy efficiency.

Virtual Digital Control Experimental System

“…VB language is object-oriented structured high-level programming language, and it is efficient and powerful for graphical interface work [5]. MATLAB is very smart and flexible to develop control Fig.…”

Optimization of x10 programs with ROSE compiler infrastructure

“…Communication optimization [14] provides an important insight on APGAS-specific optimizations by proposing various means of optimizing X10 code to reduce communication overhead. For example, it presents optimizations to avoid unnecessary copy of objects by applying scalar replacement, object splitting, and several loop transformations.…”

“…The first is to reuse the rich set of existing features provided by ROSE for analysis, transformation, and optimization. We consider whether any of the features need to be modified to align with the APGAS model and whether there are any APGAS-specific optimization such as optimizations in communication [14] to perform. The other objective is to build full support of X10 in ROSE so that ROSE users can exploit X10 for testing, experimental and related purposes.…”

Affine Loop Optimization Based on Modulo Unrolling in Chapel

“…Another communication optimization targeting the X10 language [2] achieves message aggregation in distributed loops by using a technique called scalar replacement with loop invariant code motion. Here, the compiler copies all remote portions of a block-distributed array to each locale once before the loop.…”