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9th USENIX Symposium on Operating Systems Design and Implementation, OSDI 2010

作者： Ben-Yehuda, Muli Day, Michael D. Dubitzky, Zvi Factor, Michael Har'El, Nadav Gordon, Abel Liguori, Anthony Wasserman, Orit Yassour, Ben-Ami IBM Research - Haifa Israel IBM Linux Technology Center

ISBN: (纸本)9781931971799

In classical machine virtualization, a hypervisor runs multiple operating systems simultaneously, each on its own virtual machine. In nested virtualization, a hypervisor can run multiple other hypervisors with their associated virtual machines. As operating systems gain hypervisor functionality-Microsoft Windows 7 already runs Windows XP in a virtual machine-nested virtualization will become necessary in hypervisors that wish to host them. We present the design, implementation, analysis, and evaluation of high-performance nested virtualization on Intel x86-based systems. The Turtles project, which is part of the linux/KVM hypervisor, runs multiple unmodified hypervisors (e.g., KVM and VMware) and operating systems (e.g., linux and Windows). Despite the lack of architectural support for nested virtualization in the x86 architecture, it can achieve performance that is within 6-8% of single-level (non-nested) virtualization for common workloads, through multi-dimensional paging for MMU virtualization and multi-level device assignment for I/O virtualization.

关键词： Virtualization

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Resizable, scalable, concurrent hash tables via relativistic programming

Resizable, scalable, concurrent hash tables via relativistic...

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2011 USENIX Annual Technical Conference, USENIX ATC 2011

作者： Triplett, Josh McKenney, Paul E. Walpole, Jonathan Portland State University United States IBM Linux Technology Center

ISBN: (纸本)9781931971850

We present algorithms for shrinking and expanding a hash table while allowing concurrent, wait-free, linearly scalable lookups. These resize algorithms allow Read-Copy Update (RCU) hash tables to maintain constant-time performance as the number of entries grows, and reclaim memory as the number of entries decreases, without delaying or disrupting readers. We call the resulting data structure a relativistic hash table. Benchmarks of relativistic hash tables in the linux kernel show that lookup scalability during resize improves 125x over reader-writer locking, and 56% over linux's current state of the art. Relativistic hash lookups experience no performance degradation during a resize. Applying this algorithm to memcached removes a scalability limit for get requests, allowing memcached to scale linearly and service up to 46% more requests per second. Relativistic hash tables demonstrate the promise of a new concurrent programming methodology known as relativistic programming. Relativistic programming makes novel use of existing RCU synchronization primitives, namely the wait-for-readers operation that waits for unfinished readers to complete. This operation, conventionally used to handle reclamation, here allows ordering of updates without read-side synchronization or memory barriers.

关键词： Scalability

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Verification of tree-based hierarchical read-copy update in the linux kernel

Verification of tree-based hierarchical read-copy update in ...

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2018 Design, Automation and Test in Europe Conference and Exhibition, DATE 2018

作者： Liang, Lihao McKenney, Paul E. Kroening, Daniel Melham, Tom University of Oxford United Kingdom IBM Linux Technology Center United Kingdom

ISBN: (纸本)9783981926316

Read-Copy Update (RCU) is a scalable, high-performance linux-kernel synchronization mechanism that runs low-overhead readers concurrently with updaters. Production-quality RCU implementations are decidedly non-trivial and their stringent validation is mandatory. This suggests use of formal verification. Previous formal verification efforts for RCU either focus on simple implementations or use modeling languages. In this paper, we construct a model directly from the source code of Tree RCU in the linux kernel, and use the CBMC program analyzer to verify its safety and liveness properties. To the best of our knowledge, this is the first verification of a significant part of RCU's source code - an important step towards integration of formal verification into the linux kernel's regression test suite. © 2018 EDAA.

关键词： Formal verification

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Structured deferral: Synchronization via procrastination

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Queue 2013年第5期11卷 20–39页

作者： McKenney, Paul E. IBM's Linux Technology Center United States

Developers often take a proactive approach to software design, especially those from cultures valuing industriousness over procrastination. Lazy approaches, however, have proven their value, with examples including reference counting, garbage collection, and lazy evaluation. This structured deferral takes the form of synchronization via procrastination, specifically reference counting, hazard pointers, and RCU (read-copy-update).

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Functional test data generation for Simulink-like models

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Journal of the Brazilian Computer Society 2013年第3期19卷 325-339页

作者： Araujo, Rodrigo Fraxino Delamaro, Marcio Eduardo Maldonado, Jose Carlos Instituto de Computação e Matemática Computacional Universidade de São Paulo São Carlos Brazil Linux Technology Center IBM São Paulo Brazil

Embedded systems are increasingly present in many electronic devices and is often related to critical applications. Therefore, the need for a well planned and executed testing procedure is even higher. We intend to contribute in this area by presenting an experimental evaluation of the pairwise combinatorial approach as a technique for test data generation applied specifically to Simulink-like models. In particular, we have applied our strategy to the generated source code of several models. Furthermore, a testing tool was developed to assist in the test data generation process. We show that there is no statistical significant advantages of the proposed approach over random generation of test data, but when used together they yield better results. The feasibility of the experimental results indicate that efforts can be employed in order to obtain a testing strategy integrated within a testing environment. © 2013 The Brazilian Computer Society.

关键词： Simulink

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A CPI breakdown model plug-in for optimizing application performance

A CPI breakdown model plug-in for optimizing application per...

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Workshop on Developing Tools as Plug-ins (TOPI)

作者： Rodrigo Fraxino Araujo Daniel Barboza Rafael Sene Rafael Teixeira Renato João Wainer Santos Moschetta Linux Technology Center IBM Hortolandia Brazil

Effectiveness and quality are fundamental characteristics for the development of a product. In order to support them, one needs to ensure that an application optimization level is at its best. The most widely used metric for evaluating an application performance is the CPI (Cycles Per Instruction), i.e., the number of clock cycles that takes place when an instruction is executed. We have developed a CPI Breakdown Model Plug-in, that automates the profiling of an application in the Power architecture, breaking it down into several groups of CPI events and metrics in order to identify possible bottlenecks. When analyzing such events and metrics the user can become aware of which operations are causing the processor to stall, and consequently enhance the application source code. We have discussed the adaptation of some command-line tools to be used by our CPI plug-in, which is integrated into the ibm Software Development Toolkit for Powerlinux, an Eclipse based IDE comprising a set of mainstream C/C++ development tools along with several in-house ibm ones. A case study that shows the usefulness of our approach is presented and details on how to optimize an application are discussed.

关键词： Measurement Electric breakdown Vectors Software Optimization linux Computer architecture

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Approaches towards energy-efficiency in the cloud for emerging markets

Approaches towards energy-efficiency in the cloud for emergi...

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1st IEEE International Conference on Cloud Computing for Emerging Markets, CCEM 2012

作者： Dharwar, Deepthi Bhat, Srivatsa S. Srinivasan, Vaidyanathan Sarma, Dipankar Banerjee, Pradipta Kumar IBM Linux Technology Center India

ISBN: (纸本)9781467344227

With the growing importance of the cloud computing paradigm, it is a challenge for cloud providers to keep the operational costs of the data centers in check, especially in the emerging markets, alongside catering to the customers' needs. It becomes essential to increase the operational efficiency of the data centers to be able to maximize VM (Virtual machine) offerings at minimal cost. To that end, energy-efficiency of the servers plays a critical role, as they influence the electrical and the cooling costs which constitute a major part of the total cost involved in the operation of a data center. Power-savings can be achieved at several different levels in a system: processors, memory, devices, and system-wide (involving powering down multiple components of a host all at once). At the processors level, depending on the workload trends, we can exploit technologies like DVFS (Dynamic Voltage and Frequency Scaling) or P-states when the CPU is running, and CPU sleep states (C-states) when the CPU is idle, to save power. Memory standards such as DDR3 have provisions for putting idle memory banks into low-power states. At the devices level, individual devices can be put into low-power states, controlled and co-ordinated by a run-time power management framework in the Operating System. This paper outlines the state-of-the-art in power-management technology on server hardware and describes how these raw features can be abstracted into a set of energy policies. We then explain how these policies or energy-profiles can be used to run a cloud datacener energy efficiently. Further, this paper also highlights some of the challenges involved in running cloud infrastructures in the emerging markets optimally despite some unique energy constraints. © 2012 IEEE.

关键词： Energy efficiency

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A scoping study on the 25 years of research into software testing in Brazil and an outlook on the future of the area

A scoping study on the 25 years of research into software te...

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作者： Durelli, Vinicius Humberto Serapilha Araujo, Rodrigo Fraxino Silva, Marco Aurelio Graciotto Oliveira, Rafael Alves Paes De Maldonado, Jose Carlos Delamaro, Marcio Eduardo Instituto de Ciências Matemáticas e de Computaçã o Universidade de São Paulo 13560-970 São Carlos SP Brazil Linux Technology Center IBM Brazil Hortolandia Brazil Federal Institute of Education Science and Technology of São Paulo 13872-550 São João da Boa Vista SP Brazil

Over the past 25 years the Brazilian Symposium on Software Engineering (SBES) has evolved to become the most important event on software engineering in Brazil. Throughout these years, SBES has gathered a large body of studies in software testing. Aimed at providing an insightful understanding of what has already been published in such event, we have synthesized its 25-year history of research on software testing. Using information drawn from this overview we highlighted which software testing topics have been the most extensively surveyed in SBES literature. We have also devised a co-authorship network to depict the most prolific research groups and researchers. Moreover, by performing a citation analysis of the selected studies we have tried to ascertain the importance of SBES in a wider scenario. Finally, using the information extracted from the studies, we have shed light on the state-of-the-art of software testing in Brazil and provided an outlook on its foreseeable future. © 2012 Elsevier Inc.

关键词： Software testing

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Beyond expert-only parallel programming?

Beyond expert-only parallel programming?

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2012 ACM Workshop on Relaxing Synchronization for Multicore and Manycore Scalability, RACES 2012

作者： McKenney, Paul E. IBM Linux Technology Center United States

ISBN: (纸本)9781450316323

My parallel-programming education began in earnest when I joined Sequent Computer Systems in late 1990. This education was both brief and effective: within a few short years, my co-workers and I were breaking new ground [MG92, MS93, MS98].1 Nor was I alone: Sequent habitually hired new-to-parallelism engineers and had them producing competent parallel code within a few months. Nevertheless, more than two decades later, parallel programming is perceived to be difficult to teach and learn. Is parallel programming an exception to the typical transitioning of technnology from impossible to expert-only to routine to unworthy of conscious thought? Copyright © 2012 ACM.

关键词： Parallel programming

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Retrofitted parallelism considered grossly sub-optimal 4

Retrofitted parallelism considered grossly sub-optimal

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4th USENIX Workshop on Hot Topics in Parallelism, HotPar 2012

作者： McKenney, Paul E. Linux Technology Center IBM Beaverton United States

Maze solving has been used as an example parallelprogramming problem for some years. Suggested solutions are often based on a sequential program, using work queues to allow multiple threads to explore different portions of the maze concurrently. This paper analyzes such an implementation, but also explores an alternative implementation based on strategies long used by human maze solvers. This alternative implementation outperforms the conventional approach on average, and furthermore exhibits large superlinear speedups. The paper uses insights into the cause of these superlinear speedups to derive a faster sequential algorithm, and finally considers further implications and future work. © HotPar 2012.

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