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  • 351. Zhang, Lei
    et al.
    Fu, Di
    Liu, Jiangchuan
    Ngai, Edith C.-H.
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Computer Systems.
    Zhu, Wenwu
    On energy-efficient offloading in mobile cloud for real-time video applications2017In: IEEE transactions on circuits and systems for video technology (Print), ISSN 1051-8215, E-ISSN 1558-2205, Vol. 27, no 1, p. 170-181Article in journal (Refereed)
  • 352.
    Zhang, Sizhuo
    et al.
    MIT CSAIL.
    Vijayaraghavan, Muralidaran
    MIT CSAIL.
    Wright, Andrew
    MIT CSAIL.
    Alipour, Mehdi
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Computer Systems.
    Mithal, Arvind
    MIT CSAIL.
    Constructing a Weak Memory Model2018Conference paper (Refereed)
    Abstract [en]

    Weak memory models are a consequence of the desire on part of architects to preserve all the uniprocessor optimizations while building a shared memory multiprocessor. The efforts to formalize weak memory models of ARM and POWER over the last decades are mostly empirical - they try to capture empirically observed behaviors - and end up providing no insight into the inherent nature of weak memory models. This paper takes a constructive approach to find a common base for weak memory models: we explore what a weak memory would look like if we constructed it with the explicit goal of preserving all the uniprocessor optimizations. We will disallow some optimizations which break a programmer's intuition in highly unexpected ways. The constructed model, which we call General Atomic Memory Model (GAM), allows all four load/store reorderings. We give the construction procedure of GAM, and provide insights which are used to define its operational and axiomatic semantics. Though no attempt is made to match GAM to any existing weak memory model, we show by simulation that GAM has comparable performance with other models. No deep knowledge of memory models is needed to read this paper.

  • 353. Zhang, Tianyu
    et al.
    Guan, Nan
    Deng, Qingxu
    Yi, Wang
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Computer Systems.
    Start time configuration for strictly periodic real-time task systems2016In: Journal of systems architecture, ISSN 1383-7621, E-ISSN 1873-6165, Vol. 66–67, p. 61-68Article in journal (Refereed)
  • 354. Zhou, Li
    et al.
    Hu, Xiping
    Ngai, Edith C.-H.
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Computer Systems.
    Zhao, Haitao
    Wang, Shan
    Wei, Jibo
    Leung, Victor C. M.
    A dynamic graph-based scheduling and interference coordination approach in heterogeneous cellular networks2016In: IEEE Transactions on Vehicular Technology, ISSN 0018-9545, E-ISSN 1939-9359, Vol. 65, no 5, p. 3735-3748Article in journal (Refereed)
  • 355.
    Zhou, Li
    et al.
    Natl Univ Def Technol, Coll Elect Sci & Engn, Changsha, Hunan, Peoples R China..
    Hu, Xiping
    Univ British Columbia, Dept Elect & Comp Engn, Vancouver, BC, Canada..
    Zhu, Chunsheng
    Univ British Columbia, Dept Elect & Comp Engn, Vancouver, BC, Canada..
    Ngai, Edith C. -H.
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Computer Systems.
    Wang, Shan
    Natl Univ Def Technol, Coll Elect Sci & Engn, Changsha, Hunan, Peoples R China..
    Wei, Jibo
    Natl Univ Def Technol, Coll Elect Sci & Engn, Changsha, Hunan, Peoples R China..
    Leung, Victor C. M.
    Univ British Columbia, Dept Elect & Comp Engn, Vancouver, BC, Canada..
    Green Small Cell Planning in Smart Cities under Dynamic Traffic Demand2015In: 2015 IEEE Conference on Computer Communications Workshops (INFOCOM WKSHPS), 2015, p. 618-623Conference paper (Refereed)
    Abstract [en]

    In smart cities, cellular network plays a crucial role to support connectivity anywhere and anytime. However, the communication demand brought by applications and services is hard to predict. Traffic in cellular networks might fluctuate heavily over time to time, which causes burden and waste under different traffic states. Recently, small cell was proposed to enhance spectrum efficiency and energy efficiency in cellular networks. However, how green the small cell network can be is still a question because of the accompanying interference. To meet this challenge, new green technologies should be developed. In this paper, we propose a green small cell planning scheme considering dynamic traffic states. First, we predefine a set of candidate locations for base stations (BSs) in a geographical area and generate a connection graph which contains all possible connections between BSs and user equipments (UEs). Then we adopt a heuristic to switch off small cell BSs (s-BSs) and update BS-UE connections iteratively. Finally we obtain a cell planning solution with energy efficiency without reducing spectrum efficiency and quality-of-service (QoS) requirements. The simulation results show that our dynamic small cell planning scheme has low computational complexity and achieves a significant improvement in energy efficiency comparing with the static cell planning scheme.

  • 356.
    Zhu, Chunsheng
    et al.
    Univ British Columbia, Dept Elect & Comp Engn, Vancouver, BC V5Z 1M9, Canada..
    Leung, Victor C. M.
    Univ British Columbia, Dept Elect & Comp Engn, Vancouver, BC V5Z 1M9, Canada..
    Ngai, Edith C. -H.
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Computer Systems.
    Yang, Laurence T.
    St Francis Xavier Univ, Dept Comp Sci, Antigonish, NS, Canada..
    Shu, Lei
    Guangdong Univ Petrochem Technol, Guangdong Prov Key Lab Petrochem Equipment Fault, Maoming, Peoples R China..
    Li, Xiuhua
    Univ British Columbia, Dept Elect & Comp Engn, Vancouver, BC V5Z 1M9, Canada..
    Pricing Models for Sensor-Cloud2015In: 2015 IEEE 7Th International Conference On Cloud Computing Technology And Science (Cloudcom), 2015, p. 454-457Conference paper (Refereed)
    Abstract [en]

    Incorporating ubiquitous wireless sensor networks (WSNs) and powerful cloud computing (CC), Sensor-Cloud (SC) is attracting growing attention from both academia and industry. However, pricing for SC is barely explored. In this paper, filling this gap, five SC pricing models (i.e., SCPM1, SCPM2, SCPM3, SCPM4 and SCPM5) are proposed first. Particularly, they charge a SC user, based on 1) the lease period of the user; 2) the required working time of SC; 3) the SC resources utilized by the user; 4) the volume of sensory data obtained by the user; 5) the SC path that transmits sensory data from the WSN to the user, respectively. Further, analysis is also presented to study and demonstrate the performance of the proposed SCPMs. We believe that the pricing designs and analysis performed in this work could be a very valuable guidance for future researches regarding pricing in SC.

  • 357. Zhu, Chunsheng
    et al.
    Leung, Victor C. M.
    Shu, Lei
    Ngai, Edith C.-H.
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Computer Systems.
    Green Internet of Things for Smart World2015In: IEEE Access, E-ISSN 2169-3536, Vol. 3, p. 2151-2162Article in journal (Refereed)
    Abstract [en]

    Smart world is envisioned as an era in which objects (e.g., watches, mobile phones, computers, cars, buses, and trains) can automatically and intelligently serve people in a collaborative manner. Paving the way for smart world, Internet of Things (IoT) connects everything in the smart world. Motivated by achieving a sustainable smart world, this paper discusses various technologies and issues regarding green IoT, which further reduces the energy consumption of IoT. Particularly, an overview regarding IoT and green IoT is performed first. Then, the hot green information and communications technologies (ICTs) (e.g., green radio frequency identification, green wireless sensor network, green cloud computing, green machine to machine, and green data center) enabling green IoT are studied, and general green ICT principles are summarized. Furthermore, the latest developments and future vision about sensor cloud, which is a novel paradigm in green IoT, are reviewed and introduced, respectively. Finally, future research directions and open problems about green IoT are presented. Our work targets to be an enlightening and latest guidance for research with respect to green IoT and smart world.

  • 358.
    Zhu, Yunyun
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Computer Systems. Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Division of Computer Systems.
    Caches, Transactions and Memories: Models, Coherence and Consistency2018Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Computers have brought us inestimable convenience in recent years. We have become dependent on them and more sensitive to their performance. During the past decades, we have been trying to improve program efficiency. The invention of multi-core systems is regarded as the new era of boosting performance of computer programs. When we focus on improving program efficiency, we also need to pay attention to program correctness. In some specific areas, errors, aka bugs, of programs can cause disastrous consequences. The dominant approach to bug detection is testing, which is conducted by executing a program against test cases generated based on scenarios. A bug is found when the output of the program does not match the expected output defined in the test case. One main drawback of testing is that it only shows the presence of bugs. An alternative approach is formal verification, which is a method that can exhaustively analyze the program executions and therefore show the absence of bugs. This thesis focuses on one of the main areas of formal verification - model checking. Model checking analyzes a mathematical model extracted from a program and automatically checks if it satisfies the desired properties.

    In this thesis, we first consider verifying safety and liveness properties for transactional memories. In particular, we consider the FlexTM hybrid transactional memory. We build a formal model of FlexTM, and apply a small model theorem that restricts the number of threads and variables in the model. This allows us to reduce the problem of verifying safety and liveness properties of FlexTM to checking language inclusion between the automata of FlexTM and a reference transactional memory. Second, we present a method for automatic verification of cache coherence protocols in the presence of transactional memories. We build a formal model containing a filter that represents the conflict resolution strategies of the transactional memory. We also apply a small model theorem which limits the number of cache lines of the protocol. To check cache coherence, we extend a backward reachability algorithm for infinite state systems, by removing the traces not allowed by the filter. Using this technique, we verify two cache protocols under different transactional memories respectively and conclude that they both maintain coherence.  Finally, we consider verification of safety properties of programs running over Self-Invalidate and Self-Downgrade cache coherence protocols. To that end, we define a formal model which captures the weak memory model induced by such protocols. We design an algorithm for inserting a set of optimal fences in the program, which guarantees the safety property while still maintaining the efficiency of a maximal degree.

    List of papers
    1. Verifying safety and liveness for the FlexTM hybrid transactional memory
    Open this publication in new window or tab >>Verifying safety and liveness for the FlexTM hybrid transactional memory
    Show others...
    2013 (English)Conference paper, Published paper (Refereed)
    Abstract [en]

    We consider the verification of safety (strict serializability and abort consistency) and liveness obstruction and livelock freedom) for the hybrid transactional memory framework FlexTM. This framework allows for flexible implementations of transactional memories based on an adaptation of the MESI coherence protocol. FlexTM allows for both eager and lazy conflict resolution strategies. Like in the case of Software Transactional Memories, the verification problem is not trivial as the number of concurrent transactions, their size, and the number of accessed shared variables cannot be a priori bounded. This complexity is exacerbated by aspects that are specific to hardware and hybrid transactional memories. Our work takes into account intricate behaviours such as cache line based conflict detection, false sharing, invisible reads or non-transactional instructions. We carry out the first automatic verification of a hybrid transactional memory and establish, by adopting a small model approach, challenging properties such as strict serializability, abort consistency, and obstruction freedom for both an eager and a lazy conflict resolution strategies. We also detect an example that refutes livelock freedom. To achieve this, our prototype tool makes use of the latest antichain based techniques to handle systems with tens of thousands of states.

    Place, publisher, year, edition, pages
    Grenoble, France: , 2013
    National Category
    Computer Systems
    Identifiers
    urn:nbn:se:uu:diva-213232 (URN)978-1-4503-2153-2 (ISBN)
    Conference
    Design, Automation and Test in Europe, DATE 13, Grenoble, France, March 18-22, 2013
    Projects
    UPMARC
    Available from: 2013-12-19 Created: 2013-12-19 Last updated: 2018-04-09
    2. Verification of Cache Coherence Protocols wrt. Trace Filters
    Open this publication in new window or tab >>Verification of Cache Coherence Protocols wrt. Trace Filters
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    2015 (English)In: Proc. 15th Conference on Formal Methods in Computer-Aided Design, Piscataway, NJ: IEEE , 2015, p. 9-16Conference paper, Published paper (Refereed)
    Place, publisher, year, edition, pages
    Piscataway, NJ: IEEE, 2015
    National Category
    Computer Sciences
    Identifiers
    urn:nbn:se:uu:diva-272322 (URN)978-0-9835678-5-1 (ISBN)
    Conference
    FMCAD 2015, September 27–30, Austin, TX
    Projects
    UPMARC
    Available from: 2015-09-30 Created: 2016-01-13 Last updated: 2018-04-09
    3. Fencing programs with self-invalidation and self-downgrade
    Open this publication in new window or tab >>Fencing programs with self-invalidation and self-downgrade
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    2016 (English)In: Formal Techniques for Distributed Objects, Components, and Systems, Springer, 2016, p. 19-35Conference paper, Published paper (Refereed)
    Place, publisher, year, edition, pages
    Springer, 2016
    Series
    Lecture Notes in Computer Science, ISSN 0302-9743 ; 9688
    National Category
    Computer Engineering
    Identifiers
    urn:nbn:se:uu:diva-300663 (URN)10.1007/978-3-319-39570-8_2 (DOI)000379297600002 ()978-3-319-39569-2 (ISBN)
    Conference
    FORTE 2016, June 6–9, Heraklion, Greece
    Projects
    UPMARC
    Available from: 2016-05-24 Created: 2016-08-10 Last updated: 2018-04-09Bibliographically approved
    4. Mending fences with self-invalidation and self-downgrade
    Open this publication in new window or tab >>Mending fences with self-invalidation and self-downgrade
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    2018 (English)In: Logical Methods in Computer Science, ISSN 1860-5974, E-ISSN 1860-5974, Vol. 14, no 1, article id 6Article in journal (Refereed) Published
    National Category
    Computer Sciences
    Identifiers
    urn:nbn:se:uu:diva-347675 (URN)000426512000004 ()
    Available from: 2018-01-16 Created: 2018-04-06 Last updated: 2018-05-17Bibliographically approved
5678 351 - 358 of 358
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