Real-time Reconfigurable Cache for Low-Power Embedded Systems

[[abstract]]現代的嵌入式系統通常只執行少數幾個應用程式，甚至會不停的執行單一程式。將快取組態針對某一個特定應用程式作最佳化對於效能和能量消耗都有很大的幫助。為了降低尋找最佳快取組態的時間，針對整個程式的執行，一個能找到大部份最佳組態同時可以大量降低尋找時間的演算法已經在2006年由林嘉豪等人所提出來。最近幾年有研究顯示即使是同一個應用程式，在執行的過程當中程式的行為也會隨著時間不同而有所變化。針對執行過程當中每個不同的時期給予最適當的快取組態能進一步降低系統的能量消耗。本研究提出一個方法能在一個應用程式執行當中，針對不同時期找出相對應的最佳快取組態。藉由將一個應用程式的執行分成許多固定的間隔，並且在每一段間隔裡面採用第一層指令快取的局部最佳組態，能達到明顯改善能量消耗的目的。與本論文的搜尋範圍裡所有四路關聯式快取組態的平均能量消耗相比較，本研究提出的方法平均能改善百分之91.6的能量消耗。與已經採用各自的全域最佳快取組態所造成的能量消耗相比較，平均能改善百分之5.29的能量消耗。[[abstract]]Modern embedded systems execute a small set of applications or even a single one repeatedly. Specializing cache configurations to a particular application is well-known to have great benefits on performance and power. To reduce the searching for optimal cache configuration, a most-case optimal cache configuration searching algorithm for the entire execution of an application was proposed by Lin et al. in 2006 which greatly reduces the time and power in searching. However, the fact that the behavior of an application varies from phase to phase has been shown in recent years. Tuning cache configuration to fit a target application in different phases gives a further improvement in power consumption. This work presents a mechanism which determines the optimal configurations in different phases during an execution process. By dividing an execution process into small time intervals and applying corresponding local optimal cache configuration for each interval on L1 instruction cache, this work shows that on average 91.6% energy saving is obtained by comparing with average energy consumption of all four-way set-associative caches in search space. On average 5.29% power reduction is achieved by comparing with energy consumption of benchmarks with their respective global optimal cache configurations.[[note]]碩