TURBULENCE: Complexity-effective Out-of-order Execution on GPU with Distance-based ISA

A graphics processing unit (GPU) is a processor that achieves high throughput by exploiting data parallelism. We found that many GPU workloads also contain instruction-level parallelism that can be extracted through out-of-order execution to provide additional performance improvement opportunities. We propose the TURBULENCE architecture for very low-cost out-of-order execution on GPUs. TURBULENCE consists of a novel ISA that introduces the concept of referencing operands by inter-instruction distance instead of register numbers, and a novel microarchitecture that executes the novel ISA. This distance-based operand has the property of not causing false dependencies. By exploiting this property, we achieve cost-effective out-of-order execution on GPUs without introducing expensive hardware such as a rename logic and a load-store queue. Simulation results show that TURBULENCE improves performance by 17.6% without increasing energy consumption over an existing GPU.