Boosting multi-socket cache-coherency with low-latency silicon photonic interconnects

Speed-up in computing systems today is most often accomplished by increasing parallelism in both hardware and software. Parallel applications residing wholly on a single multi-core chip generally utilize implicit inter-thread communication via shared memory managed by cache-coherency mechanisms. However, increasing parallelism by creating coherent domains across many chips poses new challenges. In this work, we illustrate the sensitivity of various applications on a theoretical four-socket system to the latency of their coherency traffic, and show that current solutions, such as Quick Path Interconnect (QPI) and HyperTransport (HT), could benefit greatly from a lower latency communication medium. Then, we propose a silicon photonic inter-chip network that achieves very low-latency and falls within a reasonable power budget.