Energy efficiency via thread fusion and value reuse

Energy consumption has become the dominant metric when it comes to designing high-performance simultaneous multi-threaded (SMT) microprocessors. The authors propose a fusion of threads to help reduce energy consumption for these future SMT microprocessors. Threads are fused by merging two dynamic instances of the same static instruction into a single instruction thereby reducing unnecessary redundant computation in the front-end of the processor. The result is that power consumption is reduced in the pipeline until the execution stage. The authors have performed full system simulation, and our simulation results show average energy reduction of 10% with little impact on performance (less than 1%). They also extend thread fusion by proposing mechanisms to reduce the number of register file accesses and functional unit activity by reusing computations when the input values of the two dynamic instances of a fused instruction are the same. Our experiments show 5% energy savings in the integer register file and 10% in the integer functional units using this technique.