A NoC-based hybrid message-passing/shared-memory approach to CMP design

Future chip-multiprocessors (CMP) will integrate many cores interconnected with a high-bandwidth and low-latency scalable network-on-chip (NoC). However, the potential that this approach offers at the transport level needs to be paired with an analogous paradigm shift at the higher levels. In particular, the standard shared-memory programming model fails to address the requirements of scalability of the many-core era. Fast data exchange among the cores and low-latency synchronization are desirable but hard to achieve in practice due to the memory hierarchy. The message-passing paradigm permits instead direct data communication and synchronization between the cores. The shared-memory could still be used for the instruction fetch. Hence, we propose a hybrid approach that combines shared-memory and message passing in a single general-purpose CMP architecture that allows efficient execution of applications developed with both parallel programming approaches. Cores fetch instructions from a hierarchical memory and exchange their data through the same memory, for compatibility with existing software, or directly through the fast NoC. We developed a fast SystemC based cycle-accurate simulator for design space explorations that we used to evaluate the performance with real benchmarks. The various components have been RTL coded and mapped to a CMOS 45 nm technology to build a silicon area model that we used to select the best architectural configurations.