Resource sharing control in Simultaneous MultiThreading microarchitectures

Simultaneous multithreading (SMT) achieves improved system resource utilization and accordingly higher instruction throughput because it exploits thread-level parallelism (TLP) in addition to conventional instruction-level parallelism (ILP). The key to high-performance SMT is to optimize the distribution of shared system resources among the threads. However, existing dynamic sharing mechanism has no control over the resource distribution, which could cause one thread to grab too many resources and clog the pipeline. Existing fetch policies address the resource distribution problem only indirectly. In this work, we strive to quantitatively determine the balance between controlling resource allocation and dynamic sharing of different system resources with their impact on the performance of SMT processors. We find that controlling the resource sharing of either the instruction fetch queue (IFQ) or the reorder buffer (ROB) is not sufficient if implemented alone. However, controlling the resource sharing of both IFQ and ROB can yield an average performance gain of 38% when compared with dynamic sharing case. The average L1 D-cache miss rate has been reduced by 33%. The average time that the instruction resides in the pipeline has been reduced by 34%. This demonstrates the power of the resource sharing control mechanism we propose.