The Impact of Resource Sharing Control on the Design of Multicore Processors

One major obstacle faced by designers when entering the multicore era is how to harness the massive computing power which these cores provide. Since Instructional-Level Parallelism (ILP) is inherently limited, one single thread is not capable of efficiently utilizing the resource of a single core. Hence, Simultaneous MultiThreading (SMT) microarchitecture can be introduced in an effort to achieve improved system resource utilization and a correspondingly higher instruction throughput through the exploitation of Thread-Level Parallelism (TLP) as well as ILP. However, when multiple threads execute concurrently in a single core, they automatically compete for system resources. Our research shows that, without control over the number of entries each thread can occupy in system resources like instruction fetch queue, instruction issue queue and/or reorder buffer, a scenario called “mutual-hindrance” execution takes place. Conversely, introducing active resource sharing control mechanisms causes the opposite situation (“mutual-benefit” execution), with a possible significant performance improvement. This demonstrates that active resource sharing control is essential for future multicore multithreading microprocessor design.