High-Speed Optical Cache Memory as Single-Level Shared Cache in Chip-Multiprocessor architectures

We present an optical bus-based Chip Multiprocessor architecture where the processing cores share an optical single-level cache unit. Physically, the optical cache is implemented externally in a separate chip located next to the CPU die. The cache interconnection system is realized through WDM optical interfaces that connect the shared cache module with the processing cores and the Main Memory via spatial-multiplexed optical waveguides; hence, the CPU-DRAM communication completely takes place in the optical domain. To evaluate the shared optical cache approach, we carry out system-level simulations of 6 realistic processor parallel workloads via the Gem5 platform. The optical cache architecture is compared against the conventional electronic Chip Multiprocessor topology that uses dedicated on-chip L1 electronic caches and a shared L2 cache. The results show significant reduction in the L1 miss rate of up to 96% for certain cases; on average, a performance speed-up of up to 20.53% or a reduction of up to 65.8% in cache capacity requirements is attained. Combined with high-bandwidth CPU-DRAM bus solutions based on optical interconnects, the proposed design is a quite promising system architecture that bridges the gap between high-speed optically connected CPU-DRAM schemes and high-speed optical memory technologies.