Increasing levels of microprocessor power dissipation call for new approaches at the architectural level that save energy by better matching of on-chip resources to application requirements. Selective cache ways provides the ability to disable a subset of the ways in a set associative cache during periods of modest cache activity, while the full cache may remain operational for more cache-intensive periods. Because this approach leverages the subarray partitioning that is already present for performance reasons, only minor changes to a conventional cache are required, and therefore, full-speed cache operation can be maintained. Furthermore, the tradeoff between performance and energy is flexible, and can be dynamically tailored to meet changing application and machine environmental conditions. We show that trading off a small performance degradation for energy savings can produce a significant reduction in cache energy dissipation using this approach.

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Although silicon optical technology is still in its formative stages, and the more near-term application is chip-to-chip communication, rapid advances have been made in the development of on-chip optical interconnects. In this paper, we investigate the integration of CMOS-compatible optical technology to on-chip cache-coherent buses in future CMPs.While not exhaustive, our investigation yields a hierarchical opto-electrical system that exploits the advantages of optical technology while abiding by projected limitations. Our evaluation shows that, for the applications considered, compared to an aggressive all-electrical bus of similar power and area, significant performance improvements can be achieved using an opto-electrical bus. This performance improvement is largely dependent on the application's bandwidth demand and on the number of implemented wavelengths per optical waveguide. We also present a number of critical areas for future work that we discover in the course of our research. OPTICAL TECHNOLOGY OVERVIEWIn this work we consider on-chip modulator-based optical transmission (Figure 1), which comprises three major components: a transmitter, a waveguide, and a receiver. We briefly describe each component, and discuss technology trends in order to estimate the specifications of future designs. We propose one such design later in Section 3. TransmitterOptical transmission requires a laser source, a modulator, and a modulator driver (electrical) circuit. The laser source provides light to the modulator, which transduces electricalThe 39th Annual IEEE/ACM International Symposium on Microarchitecture (MICRO'06) 0-7695-2732

We describe the design, analysis, and performance of an on-line

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