Loop tiling for optimization of locality and parallelism

Loop tiling is a widely used loop transformation for exposing/exploiting parallelism and data locality in modern computer architecture. It is mainly divided into two categories: fixed and parameterized. These two types of tiling technologies are systematically summarized and their advantages and disadvantages are analyzed comprehensively. Since the tile size would significantly affect the performance of the tiled code, various methods of optimal tile size selection are described. Besides, various kinds of technologies applied to multi-level tiling, parallelism exploration and imperfectly nested loops are surveyed in this paper. Based on the detailed analysis of the current researches on loop tiling technologies, several conclusions are drawn as follows: 1) How to balance the trade-off between computation complexity and generation efficiency of tiled code has not been completely solved, and how to use loop boundaries to efficiently bound the iteration spaces for data locality enhancement also needs further study. 2) Optimal tile size selection is still a difficult and open question, and it would be significant to understand the influence of different level tile size in hierarchical memory system on performance. 3) From the perspective of application, how to automatically generate effective tiled code for arbitrarily nested loops needs further research. On the other hand, how to take full advantage of shared hierarchical memory and multi-core architectures to achieve high degree of parallelism for tiled code is another interesting direction. ©, 2015, Science Press. All right reserved.