A compiler-based leakage reduction technique by power-gating functional units in embedded microprocessors

Power-gating is a technique investigated widely for reducing leakage energy in the functional units of microprocessors at the architectural level. Effective power-gating involves deactivating idle functional units for sustained periods incurring little or no performance degradation. Accurate prediction of long idle periods is essential, which, in turn, depends on the application program characteristics.In this thesis, we propose a compiler-based leakage reduction technique for embedded architectures by exploiting the well-known attributes of embedded applications, namely, small code size and intensive loops. From the control flow graph (CFG) representation of the source program, we construct a forest of loop hierarchy trees (LHTs), which capture the nesting loop properties of the program. As an LHT satisfies the partial ordering on the loop nesting, we exploit this property to identify maximal subgraphs (of functional unit idleness) in the original program. For each subgraph so found, a sleep instruction is introduced at the entry point of the corresponding code segement, thus optimizing the number of sleep instructions. The sleep instruction has one operand, a bit-vector comprised of ON/OFF controlbits for all functional units in the data path. Our target architecture is a modified ARM processor model comprising of functional units with power-gating ability. We obtained an average leakage energy reduction of 34.1% for 12 benchmarks chosen from the MiBench suite, with range of 19.5% and standard deviation of 6.5%