The SPLASH-2 suite of parallel applications has recently been released to facilitate the study of centralized and distributed shared-address-space multiprocessors. In this context, this paper has two goals. One is to quantitatively characterize the SPLASH-2 programs in terms of fundamental properties and architectural interactions that are important to understand them well. The properties we study include the computational load balance, communication to computation ratio and traffic needs, important working set sizes, and issues related to spatial locality, as well as how these properties scale with problem size and the number of processors. The other, related goal is methodological: to assist people who will use the programs in architectural evaluations to prune the space of application and machine parameters in an informed and meaningful way. For example, by characterizing the working sets of the applications, we describe which operating points in terms of cache size and problem size are representative of realistic situations, which are not, and which re redundant. Using SPLASH-2 as an example, we hope to convey the importance of understanding the interplay of problem size, number of processors, and working sets in designing experiments and interpreting their results.

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The SPLASH-2 programs: characterization and methodological considerations

Mobile computing continuously evolve through the sustained effort of many researchers. It seamlessly augments users' cognitive abilities via compute-intensive capabilities such as speech recognition, natural language processing, etc. By thus empowering mobile users, we could transform many areas of human activity. This article discusses the technical obstacles to these transformations and proposes a new architecture for overcoming them. In this architecture, a mobile user exploits virtual machine (VM) technology to rapidly instantiate customized service software on a nearby cloudlet and then uses that service over a wireless LAN; the mobile device typically functions as a thin client with respect to the service. A cloudlet is a trusted, resource-rich computer or cluster of computers that's well-connected to the Internet and available for use by nearby mobile devices. Our strategy of leveraging transiently customized proximate infrastructure as a mobile device moves with its user through the physical world is called cloudlet-based, resource-rich, mobile computing. Crisp interactive response, which is essential for seamless augmentation of human cognition, is easily achieved in this architecture because of the cloudlet's physical proximity and one-hop network latency. Using a cloudlet also simplifies the challenge of meeting the peak bandwidth demand of multiple users interactively generating and receiving media such as high-definition video and high-resolution images. Rapid customization of infrastructure for diverse applications emerges as a critical requirement, and our results from a proof-of-concept prototype suggest that VM technology can indeed help meet this requirement.

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The Case for VM-Based Cloudlets in Mobile Computing

Cloud computing has recently emerged as a new paradigm for hosting and delivering services over the Internet. Cloud computing is attractive to business owners as it eliminates the requirement for users to plan ahead for provisioning, and allows enterprises to start from the small and increase resources only when there is a rise in service demand. However, despite the fact that cloud computing offers huge opportunities to the IT industry, the development of cloud computing technology is currently at its infancy, with many issues still to be addressed. In this paper, we present a survey of cloud computing, highlighting its key concepts, architectural principles, state-of-the-art implementation as well as research challenges. The aim of this paper is to provide a better understanding of the design challenges of cloud computing and identify important research directions in this increasingly important area.

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Cloud computing: state-of-the-art and research challenges

Migrating operating system instances across distinct physical hosts is a useful tool for administrators of data centers and clusters: It allows a clean separation between hard-ware and software, and facilitates fault management, load balancing, and low-level system maintenance.By carrying out the majority of migration while OSes continue to run, we achieve impressive performance with minimal service downtimes; we demonstrate the migration of entire OS instances on a commodity cluster, recording service downtimes as low as 60ms. We show that that our performance is sufficient to make live migration a practical tool even for servers running interactive loads.In this paper we consider the design options for migrating OSes running services with liveness constraints, focusing on data center and cluster environments. We introduce and analyze the concept of writable working set, and present the design, implementation and evaluation of high-performance OS migration built on top of the Xen VMM.

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Live migration of virtual machines

This paper presents MAUI, a system that enables fine-grained energy-aware offload of mobile code to the infrastructure. Previous approaches to these problems either relied heavily on programmer support to partition an application, or they were coarse-grained requiring full process (or full VM) migration. MAUI uses the benefits of a managed code environment to offer the best of both worlds: it supports fine-grained code offload to maximize energy savings with minimal burden on the programmer. MAUI decides at run-time which methods should be remotely executed, driven by an optimization engine that achieves the best energy savings possible under the mobile device's current connectivity constrains. In our evaluation, we show that MAUI enables: 1) a resource-intensive face recognition application that consumes an order of magnitude less energy, 2) a latency-sensitive arcade game application that doubles its refresh rate, and 3) a voice-based language translation application that bypasses the limitations of the smartphone environment by executing unsupported components remotely.

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MAUI: making smartphones last longer with code offload

Operating system upgrades and patches sometimes break applications that worked fine on the older version. We present an autonomic approach to testing of OS updates while minimizing downtime, usable without local regression suites or IT expertise. Deux utilizes a dual-layer virtual machine architecture, with lightweight application process checkpoint and resume across OS versions, enabling simultaneous execution of the same applications on both OS versions in different VMs. Inputs provided by ordinary users to the production old version are also fed to the new version. The old OS acts as a pseudo-oracle for the update, and application state is automatically re-cloned to continue testing after any output discrepancies (intercepted at system call level) all transparently to users. If all differences are deemed inconsequential, then the VM roles are switched with the application state already in place. Our empirical evaluation with both LAMP and standalone applications demonstrates Deux’s efficiency and effectiveness.

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Deux: Autonomic Testing System for Operating System Upgrades

While peer-to-peer (P2P) file-sharing is a powerful and cost-effective content distribution model, most paid-for digital-content providers (CPs) rely on direct download to deliver their content. CPs such as Apple iTunes that command a large base of paying users are hesitant to use a P2P model that could easily degrade their user base into yet another free file-sharing community. We present TP2, a system that makes P2P file sharing a viable delivery mechanism for paid digital content by providing the same security properties as the currently used direct-download model. TP2 introduces the novel notion of trusted auditors (TAs) – P2P peers that are controlled by the system operator. TAs monitor the behavior of other peers and help detect and prevent formation of illegal file-sharing clusters among the CP’s user base. TAs both complement and exploit the strong authentication and authorization mechanisms that are used in TP2 to control access to content. It is important to note that TP2 does not attempt to solve the out-of-band file-sharing or DRM problems, which also exist in the direct-download systems currently in use. We analyze TP2 by modeling it as a novel game between misbehaving users who try to form unauthorized file-sharing clusters and TAs who curb the growth of such clusters. Our analysis shows that a small fraction of TAs is sufficient to protect the P2P system against unauthorized file sharing. In a system with as many as 60% of misbehaving users, even a small fraction of TAs can detect 99% of unauthorized cluster formation. We developed a simple economic model to show that even with such a large fraction of malicious nodes, TP2 can improve CP’s profits (which could translate to user savings) by 62 to 122%, even while assuming conservative estimates of content and bandwidth costs. We implemented TP2 as a layer on top of BitTorrent and demonstrated experimentally using PlanetLab that our system provides trusted P2P file sharing with negligible performance overhead.

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Can P2P Replace Direct Download for Content Distribution

Steven M. Bellovin is Professor of Computer Science at Columbia University and affiliate faculty at its law school. His research specializes in security, privacy, and related legal and policy issues. He co-authored Firewalls and Internet Security, the first book on the subject. He is a member of the National Academy of Engineering and received the USENIX “Flame” award for co-inventing Netnews. smb@cs.columbia.edu

Jason Nieh

Papers

Deux: Autonomic Testing System for Operating System Upgrades

Can P2P Replace Direct Download for Content Distribution

Making It Easier to Encrypt Your Emails.