Methodology for operation shuffling and L0 cluster generation for low energy heterogeneous VLIW processors

Abstract

Clustering L0 buffers is effective for energy reduction in the instruction memory hierarchy of embedded VLIW processors. However, the efficiency of the clustering depends on the schedule of the target application. Especially in heterogeneous or data clustered VLIW processors, determining energy efficient scheduling is more constraining. This article proposes a realistic technique supported by a tool flow to explore operation shuffling for improving generation of L0 clusters. The tool flow explores assignment of operations for each cycle and generates various schedules. This approach makes it possible to reduce energy consumption for various processor architectures. However, the computational complexity is large because of the huge exploration space. Therefore, some heuristics are also developed, which reduce the size of the exploration space while the solution quality remains reasonable. Furthermore, we also propose a technique to support VLIW processors with multiple data clusters, which is essential to apply the methodology to real world processors. The experimental results indicate potential gains of up to 27.6% in energy in L0 buffers, through operation shuffling for heterogeneous processor architectures as well as a homogeneous architecture. Furthermore, the proposed heuristics drastically reduce the exploration search space by about 90%, while the results are comparable to full search, with average differences of less than 1%. The experimental results indicate that energy efficiency can be improved in most of the media benchmarks by the proposed methodology, where the average gain is around 10% in comparison with generating clusters without operation shuffling.