A large portion of the power budget in server environments goes into the I/O subsystem -the disk array in particular. Traditional approaches to disk power management involve completely stopping the disk rotation, which can take a considerable amount of time, making them less useful in cases where idle times between disk requests may not be long enough to outweigh the overheads. This paper presents a new approach called DRPM to modulate disk speed (RPM) dynamically, and gives a practical implementation to exploit this mechanism. Extensive simulations with different workload and hardware parameters show that DRPM can provide significant energy savings without compromising much on performance. This paper also discusses practical issues when implementing DRPM on server disks.

Abstract-In this paper, we explore the possibility of using STT-RAM technology to completely replace DRAM in main memory. Our goal is to make STT-RAM performance comparable to DRAM while providing substantial power savings. Towards this goal, we first analyze the performance and energy of STT-RAM, and then identify key optimizations that can be employed to improve its characteristics. Specifically, using partial write and row buffer write bypass, we show that STT-RAM main memory performance and energy can be significantly improved. Our experiments indicate that an optimized, equal capacity STT-RAM main memory can provide performance comparable to DRAM main memory, with an average 60% reduction in main memory energy.

Long interconnects are becoming an increasingly important problem from both power and performance perspectives. This motivates designers to adopt on-chip network-based communication infrastructures and three-dimensional (3D) designs where multiple device layers are stacked together. Considering the current trends towards increasing use of chip multiprocessing, it is timely to consider 3D chip multiprocessor design and memory networking issues, especially in the context of data management in large L2 caches. The overall goal of this paper is to study the challenges for L2 design and management in 3D chip multiprocessors. Our first contribution is to propose a router architecture and a topology design that makes use of a network architecture embedded into the L2 cache memory. Our second contribution is to demonstrate, through extensive experiments, that a 3D L2 memory architecture generates much better results than the conventional two-dimensional (2D) designs under different number of layers and vertical (inter-wafer) connections. In particular, our experiments show that a 3D architecture with no dynamic data migration generates better performance than a 2D architecture that employs data migration. This also helps reduce power consumption in L2 due to a reduced number of data movements.

Main memory is a major shared resource among cores in a multicore system. If Technical Report No. 2011-002 (June 3, 2011 system configurations show that this integrated memory partitioning and scheduling approach provides better system performance than MCP and four previous memory scheduling algorithms employed alone. Averaged over 240 workloads on a 24-core system with 4 memory channels, IMPS improves system throughput by 11.1% over an application unaware scheduler and 5% over the current best scheduling policy, while incurring much lower hardware complexity than the latter.

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The anticipated explosive growth of pervasive and mobile computing devices that are typically constrained by energy has brought hardware and software techniques for energy conservation into the spotlight. While there have been several studies and proposals for energy conservation for CPUs and peripherals, energy optimization techniques for selective operating mode control of DRAMs have not been fully explored. It has been shown that for some systems as much as 90% of overall system energy (excluding I/O) is consumed by the DRAM modules; thus they serve as a good candidate for energy optimizations. Further, DRAM technology has also matured to provide several low energy operating modes (power modes), making it an opportunistic moment to conduct studies exploring the potential benefits of mode control techniques. This paper conducts an in-depth investigation of software and hardware techniques to take advantage of the DRAM mode control capabilities at a module granularity for energy savings. Using a memory system architecture capturing five different energy modes and corresponding resynchronization times, this paper presents several novel compilation techniques to both cluster the data across memory banks as well as to detect module idleness and perform energy mode transitions. In addition, hardware-assisted approaches (called self-monitoring) based on predictions of module inter-access times are proposed. These techniques are extensively evaluated using a set of a dozen benchmarks. It is shown that we get an average of 61% savings in DRAM energy using compiler-directed mode control. One of the self-monitored approaches gives as much as 89% savings (72% on the average), coming as close as 8.8% to the optimal energy savings that one can expect with DRAM module mode control. The optimization techniques are demonstrated to be invaluable for energy savings as memory technologies continue to evolve.