Abstract-With each CMOS technology generation, leakage energy has been increasing at an exponential rate and hence, managing the energy consumption of large, last-level caches is becoming a critical research issue in modern chip design. Saving cache energy in QoS systems is especially challenging, since, to avoid missing deadlines, a suitable balance needs to be made between energy saving and performance loss. We present CASHIER, a Cache Energy Saving Technique for Quality of Service Systems. Cashier uses dynamic profiling to estimate the memory subsystem energy and execution time of the program under multiple last level cache (LLC) configurations. It then reconfigures LLC to an energy efficient configuration with a view to meet the deadline. In QoS systems, allowed slack may be specified either as percentage of baseline execution time or as absolute slack and Cashier can work for both these cases. The experiments show the effectiveness of Cashier in saving cache energy. For example, for an L2 cache size of 2MB and 5% allowed-slack over baseline, the average saving in memory subsystem energy by using Cashier is 23.6%. Keywords-QoS systems, cache leakage energy saving, low power, online profiling, last level cache I. INTRODUCTION As we are entering into an era of green computing, the primary objective in chip design is shifting from achieving highest peak performance to achieving highest performanceenergy efficiency. In battery-powered mobile systems, such as cell phones and laptops, achieving energy efficiency is especially important, since these systems work on batteries which store limited energy. Moreover, since these systems also need to fulfill application quality-of-service (QoS) requirements [1, 2], a fine balance is required to meet the dual goals of energy saving and minimum performance loss. For several reasons reducing energy consumption of LLCs in QoS systems remains a significant challenge. Firstly, as the applications are becoming computation-intensive [3, 4] , the pressure on memory system is increasing and to mitigate this pressure, modern processors are using large size LLCs. Secondly, with shrinking CMOS feature size, leakage power has been increasing at an exponential rate [5]. Since leakage accounts for over 90% of the energy spent in LLCs [6], the energy consumption of LLCs is becoming a major fraction of chip energy consumption. Many existing techniques are designed to save the dynamic energy of cache, however, a large fraction of energy spent in LLCs is in the form of leakage energy, and thus, these techniques having limited utility in saving energy in LLCs. Further, the cache energy
Cashier REF uses dynamic profiling to estimate memory energy and execution time of the program under multiple last level cache (LLC) configurations.
CASHIER: A Cache Energy Saving Technique for QoS Systems
2013 26th International Conference on VLSI Design and 2013 12th International Conference on Embedded Systems
2013 26th International Conference on VLSI Design and 2013 12th International Conference on Embedded Systems
Computer Science