Reducing leakage power in peripheral circuits of L2 caches

Leakage power has grown significantly and is a major challenge in microprocessor design. Leakage is the dominant power component in second-level (L2) caches. This paper presents two architectural techniques to utilize leakage reduction circuits in L2 caches. They primarily target the leakage in the peripheral circuitry of an L2 cache and as such have to be able to cope with longer delays. One technique exploits the fact that processor activity decreases significantly after an L2 cache miss occurs and saves power during L2 miss service time. Two algorithms, a static one and an adaptive one, are proposed for deciding when to apply this leakage reduction technique. Another technique attempts to keep the peripheral circuits in a lower-power state most of the time. The results for SPEC2K benchmarks show that the first technique can achieve a 18 to 22 % reduction in L2 power consumption, on average (and up to 63%), depending on the decision algorithm. The second technique can save 25%, on average (and up to 80%). This comes with a negligible 1 to 2% performance impact, on average, depending on the technique used

高電力効率プロセッサのためのキャッシュの設計最適化

学位の種別: 課程博士審査委員会委員 : （主査）東京大学教授 中村 宏, 東京大学教授 原 辰次, 東京大学教授 石川 正俊, 東京大学准教授 近藤 正章, 東京大学准教授 品川 高廣, 東京大学准教授 入江 英嗣University of Tokyo(東京大学

Reliability in the face of variability in nanometer embedded memories

In this thesis, we have investigated the impact of parametric variations on the behaviour of one performance-critical processor structure - embedded memories. As variations manifest as a spread in power and performance, as a first step, we propose a novel modeling methodology that helps evaluate the impact of circuit-level optimizations on architecture-level design choices. Choices made at the design-stage ensure conflicting requirements from higher-levels are decoupled. We then complement such design-time optimizations with a runtime mechanism that takes advantage of adaptive body-biasing to lower power whilst improving performance in the presence of variability. Our proposal uses a novel fully-digital variation tracking hardware using embedded DRAM (eDRAM) cells to monitor run-time changes in cache latency and leakage. A special fine-grain body-bias generator uses the measurements to generate an optimal body-bias that is needed to meet the required yield targets. A novel variation-tolerant and soft-error hardened eDRAM cell is also proposed as an alternate candidate for replacing existing SRAM-based designs in latency critical memory structures. In the ultra low-power domain where reliable operation is limited by the minimum voltage of operation (Vddmin), we analyse the impact of failures on cache functional margin and functional yield. Towards this end, we have developed a fully automated tool (INFORMER) capable of estimating memory-wide metrics such as power, performance and yield accurately and rapidly. Using the developed tool, we then evaluate the #effectiveness of a new class of hybrid techniques in improving cache yield through failure prevention and correction. Having a holistic perspective of memory-wide metrics helps us arrive at design-choices optimized simultaneously for multiple metrics needed for maintaining lifetime requirements