Enabling SIMT Execution Model on Homogeneous Multi-Core System

Abstract

Single-instruction multiple-thread (SIMT) machine emerges as a primary computing device in high-perfor-mance computing, since the SIMT execution paradigm can exploit data-level parallelism effectively. This article explores the SIMT execution potential on homogeneous multi-core processors, which generally run in multiple-instruction multiple-data (MIMD) mode when utilizing the multi-core resources. We address three architecture issues in enabling SIMT execution model on multi-core processor, including multithreading execution model, kernel thread context placement, and thread divergence. For the SIMT execution model, we propose a fine-grained multithreading mechanism on an ARM-based multi-core system. Each of the processor cores stores the kernel thread contexts in its L1 data cache for per-cycle thread-switching requirement. For divergence-intensive kernels, an Inner Conditional Statement First (ICS-First) mechanism helps early re-convergence to occur and significantly improves the performance. The experiment results show that effectiveness in data-parallel processing reduces on average 36% dynamic instructions, and boosts the SIMT executions to achieve on average 1.52× and up to 5× speedups over the MIMD counterpart for OpenCL benchmarks for single issue in-order processor cores. By using the explicit vectorization optimization on the kernels, the SIMT model gains further benefits from the SIMD extension and achieves 1.71× speedup over the MIMD approach. The SIMT model using in-order superscalar processor cores outperforms the MIMD model that uses superscalar out-of-order processor cores by 40%. The results show that, to exploit data-level parallelism, enabling the SIMT model on homogeneous multi-core processors is important.