Leakage energy optimization for caches has been the target of much recent effort. In this work, we focus on instruction caches and tailor two techniques that exploit the two major factors that shape the instruction access behavior, namely, hotspot execution and sequentiality. First, we adopt a hotspot detection mechanism by profiling the branch behavior at runtime and utilize this to implement a HotSpot based Leakage Management (HSLM) mechanism. Second, we exploit code sequentiality in implementing a Just-In-Time Activation (JITA) that transitions cache lines to active mode just before they are accessed. We utilize the recently proposed drowsy cache that dynamically scales voltages for leakage reduction and implement various schemes that use different combinations of HSLM and JITA. Our experimental evaluation using the SPEC2000 benchmark suite shows that instruction cache leakage energy consumption can be reduced by 63%, 49% and 29%, on the average, as compared to an unoptimized cache, a recently proposed hardware optimized cache, and a cache optimized using compiler, respectively. Further, we observe that these energy savings can be obtained without a significant impact on performance.

In this paper we propose a novel special-purpose data memory subsystem, called Xtream-Fit, aimed at achieving high energy-delay efficiency for streaming media applications. A key novelty of Xtream-Fit is that it exposes a single customization parameter, thus enabling a very simple and yet effective design space exploration methodology. A second key contribution of this work is the ability to achieve very high energy-delay efficiency through a synergistic combination of: (1) special purpose memory subsystem components, namely, a Streaming Memory and Scratch-Pad Memory; and (2) a novel task-based execution model that exposes/enhances opportunities for efficient prefetching, and aggressive dynamic energy conservation techniques targeting on-chip and off-chip memory components. Extensive experimental results show that Xtream-Fit reduces energy-delay product by 46 % to 83%, as compared to general-purpose memory subsystems enhanced with state of the art Cache Decay and SDRAM power mode control policies.

Leakage power reduction in cache memories continues to be a critical area of research because of the promise of a significant pay-off. Various techniques have been developed so far that can be broadly categorized into state-preserving (e.g., Drowsy Caches) and non-state preserving (e.g., Cache Decay). Decay saves more leakage but also incurs dynamic power overhead in the form of induced misses. Previous work has shown that depending on the leakage vs. dynamic power trade-off, one or the other technique can be better. Several factors such as cache architecture, technology parameters and temperature, affect this trade-off. Our work proposes the first mechanism —to the best of our knowledge — that takes into account temperature in adjusting the leakage control policy at run time. At very low temperatures, leakage is relatively weak so the need to tightly control it is not as important as the need to minimize extra dynamic power (e.g., decay-induced misses) or performance loss. We use a hybrid decay+drowsy policy where the main benefit comes from decaying cache lines while the drowsy mode is used to save leakage in long decay intervals. To adapt the decay mode to temperature, we propose a simple triggering mechanism that is based on the principles of decaying 4T thermal sensors and, as such, tied to temperature. The hotter the cache is, the faster cache lines are decayed since it is beneficial to do so with very high leakage currents.Conversely, when the cache temperature is low, our mechanism defers putting cache lines in decay mode to avoid dynamic power overhead but still saves a significant amount of leakage using the drowsy mode. Our study shows that across a wide range of temperatures, the simple adaptability of our proposal yields consistently better results than either the decay mode, or drowsy mode alone, improving over the best by as much as 33%.

Increasing leakage energy consumption is an important problem for SOC-based platforms as such platforms rely on large on-chip SRAMs. While most of the previous techniques focus on hardware based leakage optimization, in this paper, we present an application access pattern oriented strategy for reducing instruction cache leakage energy. This strategy keeps track of the dynamic transitions between the procedures of a given application, and tries to keep the cache lines not used by the current procedure in a power-down state as much as possible. Our simulation results indicate significant savings in leakage energy.

Leakage energy will be the major energy consumer in future deep sub-micron designs. Especially the memory sub-system of future SOCs will be negatively affected by this trend. In order to reduce the leakage energy, memory banks are transitioned to a low-energy state when possible. This transition itself costs some energy which is termed as the transition energy. In this paper we present, as the first approach of its kind, a novel energy saving replacement policy called LRU-SEQ for instruction caches. Evaluation of the policy on various architectures in a system-level environment has shown that upto 23 % energy savings can be obtained. Considering the negligible hardware impact, LRU-SEQ offers a viable choice for an energy saving policy. 1

Leakage power reduction in cache memories continues to be a critical area of research because of the promise of a significant pay-off. Various techniques have been developed so far that can be broadly categorized into state-preserving (e.g., Drowsy Caches) and non-state preserving (e.g., Cache Decay). Decay saves more leakage but also incurs dynamic power overhead in the form of induced misses. Previous work has shown that depending on the leakage vs. dynamic power trade-off, one or the other technique can be better. Several factors such as cache architecture, technology parameters and temperature, affect this trade-off. Our work proposes the first mechanism —to the best of our knowledge — that takes into account temperature in adjusting the leakage control policy at run time. At very low temperatures, leakage is relatively weak so the need to tightly control it is not as important as the need to minimize extra dynamic power (e.g., decay-induced misses) or performance loss. We use a hybrid decay+drowsy policy where the main benefit comes from decaying cache lines while the drowsy mode is used to save leakage in long decay intervals. To adapt the decay mode to temperature, we propose a simple triggering mechanism that is based on the principles of decaying 4T thermal sensors and, as such, tied to temperature. The hotter the cache is, the faster cache lines are decayed since it is beneficial to do so with very high leakage currents.Conversely, when the cache temperature is low, our mechanism defers putting cache lines in decay mode to avoid dynamic power overhead but still saves a significant amount of leakage using the drowsy mode. Our study shows that across a wide range of temperatures, the simple adaptability of our proposal yields consistently better results than either the decay mode, or drowsy mode alone, improving over the best by as much as 33%.