An Analytical Model of Hardware Transactional Memory

This paper investigates the problem of deriving a white box performance model of Hardware Transactional Memory (HTM) systems. The proposed model targets TSX, a popular implementation of HTM integrated in Intel processors starting with the Haswell family in 2013. An inherent difficulty with building white-box models of commercially available HTM systems is that their internals are either vaguely documented or undisclosed by their manufacturers. We tackle this challenge by designing a set of experiments that allow us to shed lights on the internal mechanisms used in TSX to manage conflicts among transactions and to track their readsets and writesets. We exploit the information inferred from this experimental study to build an analytical model of TSX focused on capturing the impact on performance of two key mechanisms: the concurrency control scheme and the management of transactional meta-data in the processor's caches. We validate the proposed model by means of an extensive experimental study encompassing a broad range of workloads executed on a real system

Power Bounded Computing on Current & Emerging HPC Systems

Power has become a critical constraint for the evolution of large scale High Performance Computing (HPC) systems and commercial data centers. This constraint spans almost every level of computing technologies, from IC chips all the way up to data centers due to physical, technical, and economic reasons. To cope with this reality, it is necessary to understand how available or permissible power impacts the design and performance of emergent computer systems. For this reason, we propose power bounded computing and corresponding technologies to optimize performance on HPC systems with limited power budgets. We have multiple research objectives in this dissertation. They center on the understanding of the interaction between performance, power bounds, and a hierarchical power management strategy. First, we develop heuristics and application aware power allocation methods to improve application performance on a single node. Second, we develop algorithms to coordinate power across nodes and components based on application characteristic and power budget on a cluster. Third, we investigate performance interference induced by hardware and power contentions, and propose a contention aware job scheduling to maximize system throughput under given power budgets for node sharing system. Fourth, we extend to GPU-accelerated systems and workloads and develop an online dynamic performance & power approach to meet both performance requirement and power efficiency. Power bounded computing improves performance scalability and power efficiency and decreases operation costs of HPC systems and data centers. This dissertation opens up several new ways for research in power bounded computing to address the power challenges in HPC systems. The proposed power and resource management techniques provide new directions and guidelines to green exscale computing and other computing systems

Enhancing performance prediction robustness by combining analytical modeling and machine learning

Classical approaches to performance prediction rely on two, typically antithetic, techniques: Machine Learning (ML) and Analytical Modeling (AM). ML takes a black box ap- proach, whose accuracy strongly depends on the represen- tativeness of the dataset used during the initial training phase. Specifically, it can achieve very good accuracy in areas of the features' space that have been sufficiently ex- plored during the training process. Conversely, AM tech- niques require no or minimal training, hence exhibiting the potential for supporting prompt instantiation of the perfor- mance model of the target system. However, in order to ensure their tractability, they typically rely on a set of sim- plifying assumptions. Consequently, AM's accuracy can be seriously challenged in scenarios (e.g., workload conditions) in which such assumptions are not matched. In this paper we explore several hybrid/gray box techniques that exploit AM and ML in synergy in order to get the best of the two worlds. We evaluate the proposed techniques in case stud- ies targeting two complex and widely adopted middleware systems: a NoSQL distributed key-value store and a Total Order Broadcast (TOB) service. Copyright © 2015 ACM