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Träfflista för sökning "LAR1:cth ;pers:(Tsigas Philippas 1967)"

Sökning: LAR1:cth > Tsigas Philippas 1967

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  • Almgren, Magnus, 1972-, et al. (författare)
  • Mapping Systems Security Research at Chalmers
  • 2011
  • Ingår i: First SysSec Workshop (SysSec 2011). - 978-0-7695-4530-1 ; s. 67-70
  • Konferensbidrag (refereegranskat)abstract
    • The department of Computer Science and Engineering at Chalmers University has a long tradition of research in systems security, including security metrics, attack detection, and mitigation. We focus on security issues arising in four specific environments: (1) backbone links, (2) sensor networks, (3) the connected car, and (4) the smart grid. In this short summary we describe recent results as well as open research questions we are exploring.
  • Assarsson, Ulf, 1972-, et al. (författare)
  • Image-Space Dynamic Transparency for Improved Object Discovery in 3D Environments
  • 2006
  • Rapport (övrigt vetenskapligt)abstract
    • We present an image-space algorithm for dynamic transparency with the purpose of supporting object discovery and access in information-rich 3D visualization environments. The algorithm is based on multiple rendering passes and detects instances of object occlusion in the image-space using the fragment shader capabilities of modern programmable graphics hardware, creating alpha maps of opacity gradients around the occluded objects. In essence, the effect is somewhat similar to “X-ray vision” of a superhero. We have implemented a prototype version of our algorithm with real-time rendering performance using a number of optimizations and speedups on current graphics hardware. To evaluate its use, we have also implemented three different example applications portraying different scenarios, including abstract visualization, virtual walkthrough, and gaming. Preliminary results from an empirical user study comparing our technique to standard viewpoint controls indicate that our technique is superior in regards to object discovery efficiency. These results hold over both completion times as well as correctness of a visual search task.
  • Atalar, Aras, et al. (författare)
  • Modeling and Analyzing the Performance of Lock-Free Data Structures
  • 2014
  • Rapport (övrigt vetenskapligt)abstract
    • This paper considers the modeling and the analysis of the performance of lock-free concurrent data structures. Lock-free designs employ an optimistic conflict control approach, allowing several processes to access the shared data object at the same time. The operations on these data structures are typically designed as compositions of retry loops. Our main contribution is a new way of modeling and analyzing a general class of lock-free algorithms, achieving predictions of throughput that are close to what we observe in practice. In our model we introduce two key metrics that shape the performance of lock-free algorithms: (i) expansion in execution time of a retry due to memory congestion and (ii) number of wasted retries. We show how to compute these two metrics, and how to combine them, to calculate the throughput of an arguably large class of lock-free algorithms. Our analysis also captures the throughput performance of a lock-free algorithm when executed as part of a larger parallel application. This part of our analysis leads to an analytical method for calculating a good back-off strategy to finely tune the performance of a lock-free application. Our experimental results, based on a set of widely used concurrent data structures and on abstract lock-free designs, show that our analysis follows closely the actual code behavior. To the best of our knowledge, this is the first attempt to make ends meet between theoretical bounds on performance and actual measured throughput.
  • Atalar, Aras, et al. (författare)
  • Modeling Energy Consumption of Lock-Free Queue Implementations
  • 2015
  • Rapport (övrigt vetenskapligt)abstract
    • This paper considers the problem of modeling the energy behavior of lock-free concurrent queue data structures. Our main contribution is a way to model the energy behavior of lock-free queue implementations and parallel applications that use them. Focusing on steady state behavior we decompose energy behavior into throughput and power dissipation which can be modeled separately and later recombined into several useful metrics, such as energy per operation. Based on our models, instantiated from synthetic benchmark data, and using only a small amount of additional application specific information, energy and throughput predictions can be made for parallel applications that use the respective data structure implementation. To model throughput we propose a generic model for lock-free queue throughput behavior, based on a combination of the dequeuers’ throughput and enqueuers’ throughput. To model power dissipation we commonly split the contributions from the various computer components into static, activation and dynamic parts, where only the dynamic part depends on the actual instructions being executed. To instantiate the models a synthetic benchmark explores each queue implementation over the dimensions of processor frequency and number of threads. Finally, we show how to make predictions of application throughput and power dissipation for a parallel application using a lock-free queue requiring only a limited amount of information about the application work done between queue operations. Our case study on a Mandelbrot application shows convincing prediction results.
  • Benkner, S., et al. (författare)
  • PEPPHER : Efficient and Productive Usage of Hybrid Computing Systems
  • 2011
  • Ingår i: IEEE Micro. - IEEE Institute of Electrical and Electronics. - 0272-1732. ; 31:5, s. 28-41
  • Tidskriftsartikel (refereegranskat)abstract
    • PEPPHER, a three-year European FP7 project, addresses efficient utilization of hybrid (heterogeneous) computer systems consisting of multicore CPUs with GPU-type accelerators. This article outlines the PEPPHER performance-aware component model, performance prediction means, runtime system, and other aspects of the project. A larger example demonstrates performance portability with the PEPPHER approach across hybrid systems with one to four GPUs.
  • Casado, Lander, 1985-, et al. (författare)
  • ContikiSec: A Secure Network Layer for Wireless Sensor Networks under the Contiki Operating System
  • 2009
  • Ingår i: Proceedings of the 14th Nordic Conference on Secure IT Systems (NordSec 2009), Lecture Notes in Computer Science. - 1611-3349. - 978-3-642-04765-7 ; 5838, s. 133-147
  • Konferensbidrag (refereegranskat)abstract
    • In this paper we introduce ContikiSec, a secure network layer for wireless sensor networks, designed for the Contiki Operating System. ContikiSec has a configurable design, providing three security modes starting from confidentiality and integrity, and expanding to confidentiality, authentication, and integrity. ContikiSec has been designed to balance low energy consumption and security while conforming to a small memory footprint. Our design was based on performance evaluation of existing security primitives and is part of the contribution of this paper. Our evaluation was performed in the Modular Sensor Board hardware platform for wireless sensor networks, running Contiki. Contiki is an open source, highly portable operating system for wireless sensor networks (WSN) that is widely used in WSNs.
  • Casimiro, Antonio, et al. (författare)
  • KARYON: Towards Safety Kernels for Cooperative Vehicular Systems
  • 2012
  • Ingår i: Lecture Notes in Computer Science: Stabilization, Safety, and Security of Distributed Systems - 14th International Symposium, SSS 2012, Toronto, Canada, October 1-4, 2012. Proceedings, Springer, Lecture Notes in Computer Science. - 0302-9743. - 978-3-642-33535-8 ; 7596, s. 232-235
  • Konferensbidrag (refereegranskat)abstract
    • KARYON, a kernel-based architecture for safety-critical control, is a European project that proposes a new perspective to improve performance of smart vehicle coordination focusing on Advanced Driver Assistance Systems (ADASs) and Unmanned Aerial Systems (UAS). The key objective is to provide system solutions for predictable and safe coordination of smart vehicles that autonomously cooperate and interact in an open and inherently uncertain environment. Currently, these systems are not allowed to operate on the public roads or in the air space, as the risk of causing severe damage cannot be excluded with sufficient certainty. The impact of the project is two-fold; it will provide improved vehicle density without driver involvement and increased traffic throughput to maintain mobility without a need to build new traffic infrastructures. The results will improve interaction in cooperation scenarios while preserving safety and assessing it according to standards. The prospective project results include self-stabilizing algorithms for vehicle coordination, communication and synchronization. In addition, we aim at showing that the safety kernel can be designed to be a self-stabilizing one.
  • Cederman, Daniel, 1981-, et al. (författare)
  • A Practical Quicksort Algorithm for Graphics Processors
  • 2008
  • Rapport (övrigt vetenskapligt)abstract
    • In this paper we describe GPU-Quicksort, an efficient Quicksort algorithm suitable for highly parallel multi-core graphics processors. Quicksort has previously been considered an inefficient sorting solution for graphics processors, but we show that in CUDA, NVIDIA's programming platform for general purpose computations on graphical processors, GPU-Quicksort performs better than the fastest known sorting implementations for graphics processors, such as radix and bitonic sort. Quicksort can thus be seen as a viable alternative for sorting large quantities of data on graphics processors.
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