A reconfigurable architecture for multicore systems

Various studies concluded that bus-based multiprocessor architectures outperform Network-on-Chip (NoC) architectures when the number of processors is relatively small. On the other hand, NoC architectures offer distinct performance advantages when the number of processors is large. This led to recent proposals for hybrid architectures where each node in a mesh-style packet-switched NoC architecture contains a bus-based subsystem with a small number of processors. Experimental results using select benchmarks demonstrated that these hybrid architectures offer superior performance when compared with purely bus based or purely NoC style architectures. Our studies indicate that while a hybrid architecture is preferable, the optimal number of processors on each bus subsystem varies based on the application. This number appears to vary between 1 and 8 depending on the communication requirements of the application. Further, various applications simultaneously executing on the same system require differing numbers of processors on each bus-based subsystem to minimize the overall throughput time. In this paper, we present a new reconfigurable NoC architecture which allows scalable bus-based multiprocessor subsystems on each node in the NoC. Following configuration, the system provides a multi-bus execution environment where each processor is connected to a bus and the bus-based subsystems communicate via routers connected in a mesh-style configuration. The system can be reconfigured to vary the number of bus subsystems and the number of processors on each subsystem. Each processor contains a Level 1 (L1) cache and each bus, connected to a router, has access to a Level 2 (L2) cache. The L2 caches distributed across the network together form a large virtual L2 that can shared by all the processors in the system via the router network. We present the architecture in detail, discuss a configuration algorithm, and discuss experimental results (using the NS2 and SIMICS simulators) - - on standard and synthetic benchmarks indicating the performance advantages of the proposed architecture.