Wei-Yu Chen
Dan Bonachea
Jason Duell
ABSTRACT
Unified Parallel C (UPC) is a parallel language that uses a Single Program Multiple Data (SPMD) model of parallelism within a global address space. The global address space is used to simplify programming, especially on applications with irregular data structures that lead to fine-grained sharing between threads. Recent results have shown that the performance of UPC using a commercial compiler is comparable to that of MPI [7]. In this paper we describe a portable open source compiler for UPC. Our goal is to achieve a similar performance while enabling easy porting of the compiler and runtime, and also provide a framework that allows for extensive optimizations. We identify some of the challenges in compiling UPC and use a combination of micro-benchmarks and application kernels to show that our compiler has low overhead for basic operations on shared data and is competitive, and sometimes faster than, the commercial HP compiler. We also investigate several communication optimizations, and show significant benefits by hand-optimizing the generated code.
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Index Terms
- A performance analysis of the Berkeley UPC compiler
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Reviews
Olivier Louis Marie Lecarme
The contents of this paper are interesting, and somewhat convincing. The authors describe a compiler for the parallel language unified parallel C (UPC), using the single program multiple data (SPMD) model. They describe some aspects of the language and the model, as well as of the Berkeley UPC compiler. The rest of the paper is devoted to a comparison with the Hewlett-Packard (HP) UPC compiler. This comparison tries to demonstrate that the Berkeley compiler outperforms the HP compiler in several areas. The benchmarks used for this comparison are briefly described, and more than a dozen comparison charts present the result. This multi-author paper deserves a better presentation. As published, it contains many oversized lines, one figure is out of place, and the many comparison charts are difficult to interpret because of the different meanings of their vertical scales. If a scale means Mops/second, for example, it is better for it to be high, but if it means time in seconds, it is better for it to be low. The same problem occurs several times. It is somewhat disappointing to learn that this compiler is actually a preprocessor, since in fact, it generates C code, and relies on the performance and reliability of an available compiler. Of course, this represents an easy way to attain portability. Similarly, the use of C itself as the extended language means that the most important tool used to represent data is the ubiquitous pointer, which may not be the best solution, especially with the SPMD model. The runtime system is also of fundamental importance. In the scheme presented in this paper, it is built with two layers: the Berkeley UPC runtime system is network- and compiler-independent, while the GASNet communication system is language-independent. The Berkeley UPC compiler is not yet complete. The authors describe several optimizations they intend to implement, which will relieve the programmer from the burden of some tuning improvements. Online Computing Reviews Service
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