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Lightweight manycore processors arise to reconcile performance, energy efficiency, and scalability requirements on a single chip. Operating Systems (OSes) for these processors feature a distributed design, where isolated OS instances cooperate to mitigate programmability and portability issues coming from their architectural intricacies. Currently, OS services often resort to traditional execution flow abstractions (processes or threads) to implement small, periodic, or asynchronous functionalities. Although these abstractions considerably simplify the system design, they have a non-negotiable impact on the limited on-chip memories. Due to the memory restrictions, we argue that OS-level abstractions can be reshaped to reduce the OS memory footprint without introducing considerable overhead. In this context, we propose a complementary OS-level execution engine that supports cooperative time-sharing lightweight tasks that share a unique execution stack and features task synchronization via control flow and dependency graphs. This solution is orthogonal to the underlying execution support and provides numerous OS-level execution flows with reduced memory consumption. We implemented our engine in a distributed OS and executed experiments on a lightweight manycore. Our results show that it has the following advantages when compared to the classical thread abstraction: (i) it provides 63.2× more execution flows per MB of memory; (ii) it features less overhead to manage execution flows and system calls; (iii) it improves core utilization; and (iv) it exhibits competitive results on real-world applications. • The task-based engine reduces the OS memory footprint, providing 63x more execution flows per MB of memory. • The task-based engine improves core utilization and features less overhead to manage execution flows and system calls. • The OS latency of page invalidations is reduced with the task-based approach. • The performance of MPI applications is not significantly affected when communications are handled by the task-based engine. [ABSTRACT FROM AUTHOR]

Recently, security in software is becoming complex, especially in distributed computing. A secured and trusted environment is critically important for distributed computing. Different services and resources in the distributed system have to be secure at different levels; therefore, in this paper, we have analyzed in detail the flaws of the distributed systems, common security threats, common scenarios at which the system faces risk, and the best possible solutions to secure the distributed system. Globus security mechanism is discussed in detail as how the authentication can be done and how message confidentiality and integrity can be achieved. Every idea that radiates all sorts of solutions to this matter is verified and analyzed. This paper provides necessary knowledge to help one understand the meaning of a secure system, the security policies, and the security mechanism. [ABSTRACT FROM AUTHOR]

Single system image is a computing paradigm where a number of distributed computing resources are aggregated and presented via an interface that maintains the illusion of interaction with a single system. This approach encompasses decades of research using a broad variety of techniques at varying levels of abstraction, from custom hardware and distributed hypervisors to specialized operating system kernels and user-level tools. Existing classification schemes for SSI technologies are reviewed, and an updated classification scheme is proposed. A survey of implementation techniques is provided along with relevant examples. Notable deployments are examined and insights gained from hands-on experience are summarized. Issues affecting the adoption of kernel-level SSI are identified and discussed in the context of technology adoption literature. [ABSTRACT FROM AUTHOR]

Spatial locality of task execution is becoming important in future hardware platforms since the number of cores is steadily increasing. The large amount of cores requires an intelligent power manager and the high chip and core density requires increased thermal awareness to avoid thermal hotspots on the chip. This paper presents a lightweight task migration mechanism explicitly for distributed operating systems running on many-core platforms. As the distributed OS runs one scheduler on each core, the tasks are migrated between OS kernels within the same shared memory platform. The benefits, such as performance and energy efficiency, of task migration are achieved by re-locating running tasks on the most appropriate cores and keeping the overhead of executing such a migration sufficiently low. We investigate the overhead of migrating tasks on a distributed OS running both on a bus-based platform and a many-core NoC-with these means of measures, we can predict the task migration overhead and pinpoint the emerging bottlenecks. With the presented task migration mechanism, we intend to improve the dynamism of power and performance characteristics in distributed many-core operating systems. [ABSTRACT FROM AUTHOR]

Process migration is the act of transferring a process between two machines. It enables dynamic load distribution, fault resilience, eased system administration, and data access locality. Despite these goals and ongoing research efforts, migration has not achieved widespread use. With the increasing deployment of distributed systems in general, and distributed operating systems in particular, process migration is again receiving more attention in both research and product development. As high-performance facilities shift from supercomputers to networks of workstations, and with the ever-increasing role of the World Wide Web, we expect migration to play a more important role and eventually to be widely adopted. This survey reviews the field of process migration by summarizing the key concepts and giving an overview of the most important implementations. Design and implementation issues of process migration are analyzed in general, and then revisited for each of the case studies described: MOSIX, Sprite, Mach, and Load Sharing Facility. The benefits and drawbacks of process migration depend on the details of implementation and, therefore, this paper focuses on practical matters. This survey will help in understanding the potentials of process migration and why it has not caught on. [ABSTRACT FROM AUTHOR]

The effective management of a cluster of private workstations requires an examination of the characteristics of the usage patterns of workstations. This paper analyzes workstation-usage patterns in order to understand opportunities for exploiting idle capacity. Our study is based on traces of user workstation activity in a university environment. It identifies two areas where enhancements can be made. One identified area is the ability of a manager of the shared capacity of a workstation cluster to schedule jobs with deadline constraints. This opportunity is the result of our ability to make good predictions of the time-varying amount of capacity that is available for sharing. A prediction strategy is developed that is shown to have only a small amount of error. For the second area of enhancement, we show that it is feasible to allocate partitions of workstations for specific periods. This aids those users who on occasions need exclusive access to several machines. We examine the profile of periods during which exclusive access to partitions can be given, the rate that owners preempt users of partitions, and the distribution of interpreemption intervals. [ABSTRACT FROM AUTHOR]

Safety-critical systems typically operate in unpredictable environments. Requirements for safety and reliability are in conflict with those for real-time responsiveness. Due to unpredictable environmental needs there is no static trade-off between measures to accommodate the conflicting objectives. Instead every feature or operating system service has to be adaptive. Finally, for any design problem, there cannot be any closed-form (formal) approach taking care at the same time of (external) time constraints or deadlines, and synchronization requirements in distributed design. The reason is that these two aspects are causally independent. - In this situation we worked out a heuristic experimental, performance-driven and performance-based methodology that allows in an educated way to start with a coarse system model, with accurate logical expectations regarding its behavior. Through experiments these expectations are validated. If they are found to successfully stand the tests extended expectations and model features are generated for refining the previous design as well as its performance criteria. The refinement is done in such a way that the previous experimental configurations are extreme model cases or data profiles which both logically and experimentally are to reproduce the behavior of the previous modeling step. Thus the novel performance aspects or tendencies could then unambiguously be attributed to the influences of the refined model features. We termed this methodology Incremental Experimentation. As a general methodology it relies on a principle of comparative performance studies rather than on realistic data for narrow application ranges. The paper describes how we applied a 5-step design and refinement procedure for developing, analyzing, and evaluating our distributed operating system MELODY that exhibits novel services for supporting real-time and safety-critical applications in unpredictable environments. Experimental set-ups and theme-related findings are discussed in particular. [ABSTRACT FROM AUTHOR]