| 1. |
- Casado, Lander, 1985, et al.
(författare)
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ContikiSec: A Secure Network Layer for Wireless Sensor Networks under the Contiki Operating System
- 2009
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Ingår i: Proceedings of the 14th Nordic Conference on Secure IT Systems (NordSec 2009), Lecture Notes in Computer Science. - 1611-3349. - 9783642047657 ; 5838, s. 133 - 147
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Konferensbidrag (refereegranskat)abstract
- In this paper we introduce ContikiSec, a secure network layer forwireless sensor networks, designed for the Contiki Operating System. ContikiSechas a configurable design, providing three security modes starting fromconfidentiality and integrity, and expanding to confidentiality, authentication,and integrity. ContikiSec has been designed to balance low energy consumptionand security while conforming to a small memory footprint. Our design wasbased on performance evaluation of existing security primitives and is part ofthe contribution of this paper. Our evaluation was performed in the ModularSensor Board hardware platform for wireless sensor networks, running Contiki.Contiki is an open source, highly portable operating system for wireless sensornetworks (WSN) that is widely used in WSNs.
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| 2. |
- Elmqvist, Niklas, 1977, et al.
(författare)
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CiteWiz: a tool for the visualization of scientific citation networks
- 2007
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Ingår i: Information Visualization. - 1473-8716 .- 1473-8724. ; 6:3, s. 215-232
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Tidskriftsartikel (refereegranskat)abstract
- We present CiteWiz, an extensible framework for visualization of scientific citation networks. The system is based on a taxonomy of citation database usage for researchers, and provides a timeline visualization for overviews and an influence visualization for detailed views. The timeline displays the general chronology and importance of authors and articles in a citation database, whereas the influence visualization is implemented using the Growing Polygons technique, suitably modified to the context of browsing citation data. Using the latter technique, hierarchies of articles with potentially very long citation chains can be graphically represented. The visualization is augmented with mechanisms for parent–child visualization and suitable interaction techniques for interacting with the view hierarchy and the individual articles in the dataset. We also provide an interactive concept map for keywords and co-authorship using a basic force-directed graph layout scheme. A formal user study indicates that CiteWiz is significantly more efficient than traditional database interfaces for high-level analysis tasks relating to influence and overviews, and equally efficient for low-level tasks such as finding a paper and correlating bibliographical data.
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| 3. |
- Elmqvist, Niklas, 1977, et al.
(författare)
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Employing Dynamic Transparency for 3D Occlusion Management: Design Issues and Evaluation
- 2007
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Ingår i: Lecture Notes in Computer Science (including subseries Lecture Notes in Artificial Intelligence and Lecture Notes in Bioinformatics). - 1611-3349 .- 0302-9743. - 9783540747949 ; 4662, s. 532 - 545
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Konferensbidrag (refereegranskat)abstract
- Recent developments in occlusion management for 3D environments often involve the use of dynamic transparency, or virtual “X-ray vision”, to promote target discovery and access in complex 3D worlds. However, there are many different approaches to achieving this effect and their actual utility for the user has yet to be evaluated. Furthermore, the introduction of semi-transparent surfaces adds additional visual complexity that may actually have a negative impact on task performance. In this paper, we report on an empirical user study comparing dynamic transparency to standard viewpoint controls. Our implementation of the technique is an image-space algorithm built using modern programmable shaders to achieve real-time performance and visually pleasing results. Results from the user study indicate that dynamic transparency is superior for perceptual tasks in terms of both efficiency and correctness.
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| 4. |
- Sundell, Håkan, 1968, et al.
(författare)
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NOBLE: non-blocking programming support via lock-free shared abstract data types
- 2009
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Ingår i: SIGARCH Computer Architecture News. - : ACM, Association for Computing Machinery, Inc.. - 0163-5964 .- 1943-5851. ; 36:5, s. 80-87
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Tidskriftsartikel (refereegranskat)abstract
- An essential part of programming for multi-core and multi-processor includes ef cient and reliable means for sharing data. Lock-free data structures are known as very suitable for this purpose, although experienced to be very complex to design. In this paper, we present a software library of non-blocking abstract data types that have been designed to facilitate lock-free programming for non-experts. The system provides: i) ef cient implementations of the most commonly used data types in concurrent and sequential software design, ii) a lock-free memory management system, and iii) a run time-system. The library provides clear semantics that are at least as strong as those of corresponding lock-based implementations of the respective data types. Our software library can be used for facilitating lockfree programming; its design enables the programmer to: i) replace lock-based components of sequential or parallel code easily and ef ciently , ii) use well-tuned concurrent algorithms inside a software or hardware transactional system. In the paper we describe the design and functionality of the system. We also provide experimental results that show that the library can considerably improve the performance of software systems.
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| 5. |
- Ha, Phuong, 1976, et al.
(författare)
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The Synchronization Power of Coalesced Memory Accesses
- 2008
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Ingår i: Lecture Notes in Computer Science (including subseries Lecture Notes in Artificial Intelligence and Lecture Notes in Bioinformatics). - Berlin, Heidelberg : Springer Berlin Heidelberg. - 1611-3349 .- 0302-9743. - 9783540877783 ; 5218, s. 320-334
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Konferensbidrag (refereegranskat)abstract
- Multicore processor architectures have established themselves as the new generation of processor architectures. As part of the one core to many cores evolution, memory access mechanisms have advanced rapidly. Several new memory access mechanisms have been implemented in many modern commodity multicore processors. Memory access mechanisms, by devising how processing cores access the shared memory, directly influence the synchronization capabilities of the multicore processors. Therefore, it is crucial to investigate the synchronization power of these new memory access mechanisms.This paper investigates the synchronization power of coalesced memory accesses, a family of memory access mechanisms introduced in recent large multicore architectures like the CUDA graphics processors. We first design three memory access models to capture the fundamental features of the new memory access mechanisms. Subsequently, we prove the exact synchronization power of these models in terms of their consensus numbers. These tight results show that the coalesced memory access mechanisms can facilitate strong synchronization between the threads of multicore processors, without the need of synchronization primitives other than reads and writes. In the case of the contemporary CUDA processors, our results imply that the coalesced memory access mechanisms have consensus numbers up to sixteen.
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| 6. |
- Ha, Phuong, 1976, et al.
(författare)
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Wait-free Programming for General Purpose Computations on Graphics Processors
- 2008
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Ingår i: the Proceedings of the 22th International Parallel and Distributed Symposium (IPDPS 2008). - 1530-2075. - 9781424416936 ; , s. 1-12
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Konferensbidrag (refereegranskat)abstract
- The fact that graphics processors (GPUs) are today’s most powerful computational hardware for the dollar has motivated researchers to utilize the ubiquitous and powerful GPUs for general-purpose computing. Recent GPUs feature the single-program multiple-data (SPMD) multicore architecture instead of the single-instruction multiple-data (SIMD). However, unlike CPUs, GPUs devote their transistors mainly to data processing rather than data caching and flow control, and consequently most of the powerful GPUs with many cores do not support any synchronization mechanisms between their cores. This prevents GPUs from being deployed more widely for general-purpose computing. This paper aims at bridging the gap between the lack of synchronization mechanisms in recent GPU architectures and the need of synchronization mechanisms in parallel applications. Based on the intrinsic features of recent GPU architectures, we construct strong synchronization objects like wait-free and t-resilient read-modify-write objects for a general model of recent GPU architectures without strong hardware synchronization primitives like test-and-set and compare-and-swap. Accesses to the wait-free objects have time complexity O(N), whether N is the number of processes. Our result demonstrates that it is possible to construct wait-free synchronization mechanisms for GPUs without the need of strong synchronization primitives in hardware and that wait-free programming is possible for GPUs.
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| 7. |
- Elmqvist, Niklas, 1977, et al.
(författare)
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DataMeadow: a visual canvas for analysis of large-scale multivariate data
- 2008
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Ingår i: Information Visualization. - : SAGE Publications. - 1473-8716 .- 1473-8724. ; 7:1, s. 18-33
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Tidskriftsartikel (refereegranskat)abstract
- Supporting visual analytics of multiple large-scale multidimensional data sets requires a high degree of interactivity and user control beyond the conventional challenges of visualizing such data sets. We present the DataMeadow, a visual canvas providing rich interaction for constructing visual queries using graphical set representations called DataRoses. A DataRose is essentially a starplot of selected columns in a data set displayed as multivariate visualizations with dynamic query sliders integrated into each axis. The purpose of the DataMeadow is to allow users to create advanced visual queries by iteratively selecting and filtering into the multidimensional data. Furthermore, the canvas provides a clear history of the analysis that can be annotated to facilitate dissemination of analytical results to stakeholders. A powerful direct manipulation interface allows for selection, filtering, and creation of sets, subsets, and data dependencies. We have evaluated our system using a qualitative expert review involving two visualization researchers. Results from this review are favorable for the new method.
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| 8. |
- Keramatian, Amir, 1990, et al.
(författare)
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MAD-C: Multi-stage Approximate Distributed Cluster-Combining for Obstacle Detection and Localization
- 2019
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Ingår i: Lecture Notes in Computer Science (including subseries Lecture Notes in Artificial Intelligence and Lecture Notes in Bioinformatics). - Cham : Springer International Publishing. - 1611-3349 .- 0302-9743. ; 11339 LNCS, s. 312-324
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Konferensbidrag (refereegranskat)abstract
- Efficient distributed multi-sensor monitoring is a key feature of upcoming digitalized infrastructures. We address the problem of obstacle detection, having as input multiple point clouds, from a set of laser-based distance sensors; the latter generate high-rate data and can rapidly exhaust baseline analysis methods, that gather and cluster all the data. We propose MAD-C, a distributed approximate method: it can build on any appropriate clustering, to process disjoint subsets of the data distributedly; MAD-C then distills each resulting cluster into a data-summary. The summaries, computable in a continuous way, in constant time and space, are combined, in an order-insensitive, concurrent fashion, to produce approximate volumetric representations of the objects. MAD-C leads to (i) communication savings proportional to the number of points, (ii) multiplicative decrease in the dominating component of the processing complexity and, at the same time, (iii) high accuracy (with RandIndex >0.95), in comparison to its baseline counterpart. We also propose MAD-C-ext, building on the MAD-C’s output, by further combining the original data-points, to improve the outcome granularity, with the same asymptotic processing savings as MAD-C.
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| 9. |
- Nguyen, Dang Nhan, 1983, et al.
(författare)
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ParMarkSplit : A Parallel Mark-Split Garbage Collector Based on a Lock-Free Skip-List
- 2014
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Ingår i: Lecture Notes in Computer Science (including subseries Lecture Notes in Artificial Intelligence and Lecture Notes in Bioinformatics). - Cham : Springer. - 1611-3349 .- 0302-9743. - 9783319144719 - 9783319144726 ; 8878, s. 372-387
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Konferensbidrag (refereegranskat)abstract
- Mark-split is a garbage collection algorithm that combines advantages of both the mark-sweep and the copying collection algorithms. In this paper, we present a parallel mark-split garbage collector (GC). Our parallel design introduces and makes use of an efficient concurrency control mechanism for handling the list of free memory intervals. This mechanism is based on a lock-free skip-list design which supports an extended set of operations. Beside basic operations, it can perform a composite one that can search and remove and also insert two elements atomically. We have implemented the parallel mark-split GC in OpenJDK’s HotSpot virtual machine. We experimentally evaluate our collector and compare it with the default concurrent mark-sweep GC in HotSpot, using the DaCapo benchmarks, on two contemporary multiprocessor systems; one has 12 Intel Nehalem cores with HyperThreading and the other has 48 AMD Bulldozer cores. The evaluation shows that our parallel mark-split keeps the characteristics of the sequential mark-split, that it performs better than the concurrent mark-sweep in applications that have low live/garbage ratio, and have live objects locating contiguously, therefore being marked consecutively. Our parallel mark-split performs significantly better than a trivial parallelization based on locks in terms of both collection time and scalability.
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| 10. |
- Sundell, Håkan, 1968, et al.
(författare)
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Brushing the Locks out of the Fur: A Lock-Free Work Stealing Library
- 2009
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Ingår i: econd Swedish Workshop on Multi-Core Computing, (MCC '09).
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Konferensbidrag (refereegranskat)abstract
- We present a lock-free version of the light-weight userleveltask management library called Wool, in an aim toshow that even extremely well tuned, in terms of synchronization,applications can benefit from lock-free programming.Explicit multi-threading is an efficient way to exploitthe offered parallelism of multi-core and multi-processorbased systems. However, it can sometimes be hard to expressthe inherited parallelism in programs using a limitednumber of long lived threads. Often it can be more straightforwardto dynamically create a large number of small tasksthat in turn automatically execute on the available threads.Wool is a promising and efficient library and frameworkthat allows the programmer to create user tasks in C witha very low overhead. The library automatically executestasks and balances the load evenly on a given number ofthreads by utilizing work stealing techniques. However, thesynchronization for stealing tasks is based on mutual exclusionwhich is known to limit parallelism and efficiency. Wehave designed and implemented a new lock-free algorithmfor synchronization of stealing tasks in Wool. Experimentsshow similar or significantly improved performance on a setof benchmarks executed on a multi-core platform.
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