Thermal management of on-chip caches through power density minimization

Various architectural power reduction techniques have been proposed for on-chip caches in the last decade. In this paper, we first show that these power reduction techniques can be suboptimal when thermal effects are considered. Then, we propose a thermal-aware cache power-down technique that minimizes the power density of the active parts by turning off alternating rows of memory cells instead of entire banks. The decrease in the power density lowers the temperature, which then exponentially reduces the leakage. Thus, leakage power of the active parts is reduced in addition to the power eliminated from the parts that are turned off. Simulations based on SPEC2000, NetBench, and MediaBench applications in a 70-nm technology show that the proposed thermal-aware architecture can reduce the total energy consumption by 53% compared to a conventional cache, and 14% compared to a cache architecture with thermal-unaware power reduction scheme. Second, we show a block permutation scheme that can be used during the design of the caches to maximize the distance between blocks with consecutive addresses. Because of spatial locality, blocks with consecutive addresses are likely to be accessed within a short time interval. By maximizing the distance between such blocks, we minimize the power density of the hot spots in the cache, and hence reduce the peak temperature. This, in return, results in an average leakage power reduction of 8.7% compared to a conventional cache without affecting the dynamic power and the latency. Overall, both of our architectures add no extra run-time penalty compared to the thermal-unaware power reduction schemes, yet they result in a significant reduction in the total energy consumption of a cache.