Accelerating Cache Coherence in Manycore Processor through Silicon Photonic Chiplet

Cache coherence overhead in manycore systems is becoming prominent with the increase of system scale. However, traditional electrical networks restrict the efficiency of cache coherence transactions in the system due to the limited bandwidth and long latency. Optical network promises high bandwidth and low latency, and supports both efficient unicast and multicast transmission, which can potentially accelerate cache coherence in manycore systems. This work proposes a novel photonic cache coherence network with a physically centralized logically distributed directory called PCCN for chiplet-based manycore systems. PCCN adopts a channel sharing method with a contention solving mechanism for efficient long-distance coherence-related packet transmission. Experiment results show that compared to state-of-the-art proposals, PCCN can speed up application execution time by 1.32x, reduce memory access latency by 26%, and improve energy efficiency by 1.26x, on average, in a 128-core system.