Karim Djemame

Karim Djemame
University of Leeds · School of Computing

About

159
Publications
14,228
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1,622
Citations

Publications

Publications (159)
Article
Full-text available
Reducing the number of data accesses in memory hierarchy is of paramount importance on modern computer systems. One of the key optimizations addressing this problem is loop tiling, a well-known loop transformation that enhances data locality in memory hierarchy. The selection of an appropriate tile size is tackled by using both static (analytical)...
Article
Efficient application scheduling is critical for achieving high performance in heterogeneous computing systems. This problem has proved to be NP-complete even for the homogeneous case, heading research efforts in obtaining low complexity heuristics that produce good quality schedules. Such an example is HEFT, one of the most efficient list scheduli...
Conference Paper
Loop tiling is a well-known loop transformation that enhances data locality in memory hierarchy. In this paper, we initially reveal two important inefficiencies of current analytical loop tiling models and we provide the theoretical background on how current analytical models can address these inefficiencies. To this end, we propose a new analytica...
Book
Full-text available
Proceedings of the 37th Annual UK Performance Engineering workshop, held online on 15th December 2021.
Article
Full-text available
The advent of data proliferation and electronic devices gets low execution time and energy consumption software in the spotlight. The key to optimizing software is the correct choice, order as well as parameters of optimization transformations that has remained an open problem in compilation research for decades for various reasons. First, most of...
Book
Heterogeneous Computing Architectures: Challenges and Vision provides an updated vision of the state-of-the-art of heterogeneous computing systems, covering all aspects related to their design: from the architecture and programming models to hardware/software integration and orchestration to real-time and security requirements. Evolution of computi...
Article
Hardware in High Performance Computing environments in recent years have increasingly become more heterogeneous in order to improve computational performance. An additional aspect of such systems is the management of power and energy consumption. The increase in heterogeneity requires middleware and programming model abstractions to eliminate addit...
Chapter
The Transparent heterogeneous hardware Architecture deployment for eNergy Gain in Operation (TANGO) project’s goal is to characterise factors which affect power consumption in software development and operation for Heterogeneous Parallel Hardware (HPA) environments. Its main contribution is the combination of requirements engineering and design mod...
Article
Energy consumption in Cloud and High Performance Computing platforms is a significant issue and affects aspects such as the cost of energy and the cooling of the data centre. Host level monitoring and prediction provides the groundwork for improving energy efficiency through the placement of workloads. Monitoring must be fast and efficient without...
Article
Full-text available
With the increasing cost of electricity, Cloud providers consider energy con- sumption as one of the major cost factors to be maintained within their infrastructure. Consequently, various proactive and reactive management mechanisms are used to efficiently manage the cloud resources and reduce the energy consumption and cost. These mechanisms suppo...
Article
Full-text available
The persistent development of Cloud computing attracts individuals and organisations to change their IT strategies. According to this development and the incremental demand of using Cloud computing, Cloud providers continuously update the Cloud infrastructure to fit the incremental demands. Recently, accelerator units, such as Graphics Processing U...
Conference Paper
Hardware in HPC environments in recent years has become ever more heterogeneous in order to improve computational performance and as an aspect of managing power and energy constraints. This increase in heterogeneity requires middleware abstractions to eliminate additional complexities that it brings. In this paper we present a self-adaptation frame...
Conference Paper
Full-text available
Virtual Machines (VMs) auto-scaling is an important technique to provision additional resource capacity in a Cloud environment. It allows the VMs to dynamically increase or decrease the amount of resources as needed in order to meet Quality of Service (QoS) requirements. However, the auto-scaling mechanism can be time-consuming to initiate (e.g. in...
Conference Paper
Full-text available
Virtual Machines (VMs) live migration is one of the important approaches to improve resource utilisation and support energy efficiency in Clouds. However, VMs live migration leads to performance loss and additional costs due to increased migration time and energy overhead. This paper introduces a Performance and Energy-based Cost Prediction Framewo...
Conference Paper
Full-text available
Pricing mechanisms employed by different service providers significantly influence the role of cloud computing within the IT industry. With the increasing cost of electricity, Cloud providers consider power consumption as one of the major cost factors to be maintained within their infrastructures. Consequently, modelling a new pricing mechanism tha...
Conference Paper
Full-text available
Pricing mechanisms employed by different service providers significantly influence the role of cloud computing within the IT industry. With the increasing cost of electricity, Cloud providers consider power consumption as one of the major cost factors to be maintained within their infrastructures. Consequently, modelling a new pricing mechanism tha...
Chapter
“Cloud computing” and “Big Data” are amongst the most hyped-up terms and buzzwords of the moment. After decades in which individuals and companies used to host their data and applications using their own IT infrastructure, the world has seen the stunning transformation of the Internet. Major shifts occurred when these infrastructures began to be ou...
Conference Paper
Full-text available
Energy consumption is a key concern in cloud computing. The paper reports on a cloud architecture to support energy efficiency at service construction, deployment, and operation. This is achieved through SaaS, PaaS and IaaS intra-layer self-adaptation in isolation. The self-adaptation mechanisms are discussed, as well as their implementation and ev...
Conference Paper
The excessive use of energy consumption in Cloud infrastructures has become one of the major cost factors for Cloud providers to maintain. In order to enhance the energy efficiency of Cloud resources, proactive and reactive management tools are used. However, these tools need to be supported with energy-awareness not only at the physical machine (P...
Article
Cloud computing providers resort to a variety of techniques to improve energy consumption at each level of the cloud computing stack. Most of these techniques consider resource-level energy optimisation at IaaS layer. This paper argues energy gains can be obtained by creating a cooperation between the PaaS layer (in charge of hosting the applicatio...
Article
Full-text available
The energy consumption of cloud computing continues to be an area of significant concern as data center growth continues to increase. This paper reports on an energy efficient interoperable cloud architecture realised as a cloud toolbox that focuses on reducing the energy consumption of cloud applications holistically across all deployment models....
Conference Paper
Full-text available
Internet Service Providers (ISPs) provide Internet access to their subscribers with agreed terms and conditions. Quality of Service (QOS) is the mechanism to appraise subscribers satisfaction on their provided services. The current business model between ISPs has increased competition on the bandwidth prices, while the negotiations between them are...
Article
Cloud service providers offer access to their resources through formal Service Level Agreements (SLA), and need wellbalanced infrastructures so that they can maximise the Quality of Service (QoS) they offer and minimise the number of SLA violations. This paper focuses on a specific aspect of risk assesment as applied in cloud computing: methods wit...
Conference Paper
Energy consumption is a key concern in cloud computing. The paper reports on a cloud architecture to support energy efficiency at service construction, deployment, and operation. This is achieved through SaaS, PaaS and IaaS intra-layer self-adaptation in isolation. The self-adaptation mechanisms are discussed, as well as their implementation and ev...
Conference Paper
Energy consumption in Cloud computing is a significant issue and affects aspects such as the cost of energy, cooling in the data center and the environmental impact of cloud data centers. Monitoring and prediction provides the groundwork for improving the energy efficiency of data centers. This monitoring however is required to be fast and efficien...
Conference Paper
Full-text available
The paper is concerned with the issue of how software systems actually use Heterogeneous Parallel Architectures (HPAs), with the goal of optimizing power consumption on these resources. It argues the need for novel methods and tools to support software developers aiming to optimise power consumption resulting from designing, developing, deploying a...
Conference Paper
Energy consumption in Cloud computing is a significant issue in regards to aspects such as the cost of energy, cooling in the data center and the environmental impact of cloud data centers. Smart grids offers the prospect of dynamic costs for a data center’s energy usage. These dynamic costs can be passed on to Cloud users providing incentives for...
Article
Mobility plays a key role in the forwarding of data in delay-tolerant mobile ad hoc networks, as it is mobility that gives rise to local connection opportunities. Different patterns of mobility may give rise to different opportunity for communication, and different protocols may be more effective in particular situations. It is thus becoming increa...
Article
Full-text available
Cloud Computing has changed the way in which people use the IT resources today. Now, instead of buying their own IT resources, they can use the services offered by Cloud Computing with reasonable costs based on a “pay-per-use” model. However, with the wide adoption of Cloud Computing, the costs for maintaining the Cloud infrastructure have become a...
Conference Paper
Full-text available
Internet Service Providers (ISPs) provide Internet access to their subscribers with agreed terms and conditions. Quality of Service (QOS) is the mechanism to appraise subscribers satisfaction on their provided services. The current business model between ISPs has increased competition on the bandwidth prices, while the negotiations between them are...
Conference Paper
Energy consumption in Cloud computing is a significant issue in regards to aspects such as the cost of energy, cooling in the data center and the environmental impact of cloud data centers. Smart grids offers the prospect of dynamic costs for a data center's energy usage. These dynamic costs can be passed on to Cloud users providing incentives for...
Conference Paper
Energy consumption in Cloud computing is a significant issue in regards to aspects such as the cost of energy, cooling in the data center and the environmental impact of cloud data centers. Smart grids offers the prospect of dynamic costs for a data center’s energy usage. These dynamic costs can be passed on to Cloud users providing incentives for...
Conference Paper
The energy consumption of Cloud computing continues to be an area of significant concern as data center growth continues to increase. This paper reports on an energy efficient interoperable Cloud architecture realized as a Cloud toolbox that focuses on reducing the energy consumption of Cloud applications holistically across all deployments models....
Conference Paper
Cloud Computing has changed the way in which people use the IT resources today. Now, instead of buying their own IT resources, they can use the services offered by Cloud Computing with reasonable costs based on a “pay-per-use” model. However, with the wide adoption of Cloud Computing, the costs for maintaining the Cloud infrastructure have become a...
Conference Paper
The emerging transformation from a product oriented economy to a service oriented economy based on Cloud environments envisions new scenarios where actual QoS (Quality of Service) mechanisms need to be redesigned. In such scenarios new models to negotiate and manage Service Level Agreements (SLAs) are necessary. An SLA is a formal contract which de...
Conference Paper
Full-text available
Autonomic management within autonomic computing framework is considered as the future and viable solution for many appliances, either in software or hardware. Nevertheless, its current research application in computer networks is mainly visible in the intra domain space, and less attention is given to inter domain between one core network and anoth...
Article
In order to fully exploit the concept of Smart Home, challenges associated with multiple device management in consumer facing applications have to be addressed. Specific to this is the management of resource usage in the home via the improved utilization of devices, this is achieved by integration with the wider environment they operate in. The tra...
Conference Paper
The paper argues the need to provide novel methods and tools to support software developers aiming to optimise energy efficiency and minimise the carbon footprint resulting from designing, developing, deploying and running software in Clouds, while maintaining other quality aspects of software to adequate and agreed levels. A cloud architecture to...
Article
WS-Agreement is a language and protocol designed for creating service-level agreements (SLAs) based on initial offers, and for monitoring those offers at runtime. The definition of WS-Agreement protocol is very general and does not contemplate the possibility of changing an agreement at runtime. This paper presents extensions of the WS-Agreement sp...
Article
Full-text available
The anticipated introduction of new forms of intelligent transport systems (ITS) represents a significant opportunity for increased cooperative mobility and sociotechnical changes within the transport system. Although such technologies are currently technically feasible, various socioeconomic and environmental barriers impede their arrival. This pa...
Article
Grids offer best effort services to users. Service level agreements offer the opportunity to provide guarantees upon services offered, in such a way that it captures the users' requirements, while also considering concerns of the service providers. This is achieved via a process of converging requirements and service cost values from both sides tow...
Article
Service providers offer access to resources and services in distributed environments such as Grids and Clouds through formal Service level Agreements (SLA), and need well-balanced infrastructures so that they can maximise the Quality of Service (QoS) they offer and minimise the number of SLA violations. We propose a mathematical model to predict th...
Conference Paper
The importance of Quality of Service management in service oriented environments has brought the need of QoS aware solutions. Proactive adaptation approaches enable composite services to detect in advance, according to their QoS values, the need for a change in order to prevent upcoming problems, and maintain the functional and quality levels of th...
Conference Paper
Trust and risk are often seen in proportion to each other; as such, high trust may induce low risk and vice versa. However, recent research argues that trust and risk relationship is implicit rather than proportional. Considering that trust and risk are implicit, this paper proposes for the first time a novel approach to view trust and risk on a ba...
Conference Paper
Resource usage in Clouds can be improved by deploying applications with richer defined requirements. Such "richer requirements" involve wider application / user specific context capture expressed in interrelated models. The use of model based requirements is presented using input from test-beds monitoring resource use in terms of Trust, Risk, Eco-E...
Conference Paper
In order to improve service execution in Clouds, the management of Cloud Infrastructure has to take measures to adhere to Service Level Agreements and Business Level Objectives, from the application layer through to how services are supported at the lowest hardware levels. In this paper a risk model methodology and holistic management approach is d...
Conference Paper
Service-orientation is effective at managing complexity and dynamicity at a programmatic level, but there is still much work to be done in understanding and improving the trust that users place in a system's outputs, and the extent to which they understand the associated risks of decisions recommended by a system. This is crucial if we are to impro...
Conference Paper
Service-Oriented Computing (SOC) provides a flexible framework in which applications may be built up from services, often distributed across a network. One of the promises of SOC is that of Dynamic Binding where abstract consumer requests are bound to concrete service instances at runtime, thereby offering a high level of flexibility and adaptabili...
Conference Paper
Mobility models play a key role in the evaluation of wireless network protocols and applications. Simulation results obtained with an unrealistic model may not reflect the true performance of a system in real environments. Besides, different environments may be characterized by different patterns of mobility which require simulation scenarios to be...
Conference Paper
Increase emphasis on Quality of Service and highly changing environments make management of composite services a time consuming and complicated task. Adaptation approaches aim to mitigate the management problem by adjusting composite services to the environment conditions, maintaining functional and quality levels, and reducing human intervention....
Conference Paper
The increasing popularity of virtual computing environments such as Cloud and Grid computing is helping to drive the realization of ubiquitous and pervasive computing. However, as computing becomes more entrenched in everyday life, the concepts of trust and risk become increasingly important. In this paper, we propose a new graph-based theoretical...
Conference Paper
As modern information systems become increasingly business- and safety-critical, it is extremely important to improve both the trust that a user places in a system and their understanding of the risks associated with making a decision. This paper presents the STRAPP framework, a generic framework that supports both of these goals through the use of...
Article
Full-text available
Cloud computing technologies have reached a high level of development, yet a number of obstacles still exist that must be overcome before widespread commercial adoption can become a reality. In a cloud environment, end users requesting services and cloud providers negotiate service-level agreements (SLAs) that provide explicit statements of all exp...
Conference Paper
Full-text available
We introduce and define the concept of recontextualization for cloud applications by extending contextualization, i.e. the dynamic configuration of virtual machines (VM) upon initialization, with autonomous updates during runtime. Recontextualization allows VM images and instances to be dynamically re-configured without restarts or downtime, and th...
Article
Full-text available
New VM instances are created from static templates that contain the basic configuration of the VM to achieve elasticity with regards to capacity. Instance specific settings can be injected into the VM during the deployment phase through means of contextualization. So far this is limited to a single data source and data remains static throughout the...
Conference Paper
Automated control of Cloud Service Level Agreements (SLA) is typically focused on Quality of Service (QoS) management and monitoring of the Cloud Infrastructure in-line with the SLA. Using risk assessments to bridge the needs of the Service Provider and Infrastructure Provider is one way in which the management of the whole Cloud SLA life-cycle can...
Article
This research sets out to help computational modellers, to select the most cost effective cloud service provider. A novel quality-aware computational cloud management service (QAComPMS) is proposed and evaluated. This selects the best (cheapest) cloud provider's service and then automatically runs it. QaComPMS includes an integrated ontology that p...
Chapter
The emerging transformation from a product oriented economy to a service oriented economy based on Cloud environments envisions new scenarios where actual QoS mechanisms need to be redesigned. In such scenarios new models to negotiate and manage Service Level Agreements (SLAs) are necessary. An SLA is a formal contract which defines acceptable serv...
Conference Paper
Cloud computing provides outsourcing of resources bringing economic benefits. The outsourcing however does not allow data owners to outsource the responsibility of confidentiality, integrity and access control, as it still is the responsibility of the data owner. As cloud computing is transparent to both the programmers and the users, it induces ch...
Conference Paper
We introduce our Grid broker that uses SLAs in job submission with the aim of ensuring jobs are computed on time and on budget. We demonstrate our broker’s ability to perform negotiation and to select preferentially higher priority jobs, in a tender market and discuss the architecture that makes this possible. We additionally show the effects of re...
Conference Paper
In this paper, we seek to improve understanding of human mobility patterns in environments having definite and highly organized structure, such as shopping malls. We present a method to identify individuals expressing different mobility patterns. Besides, to understand better the role of groups of message carriers expressing different mobility patt...
Conference Paper
Service-Oriented Computing (SOC) provides a flexible framework in which applications are built up from services, often distributed across a network. One of the promises of SOC is that of Dynamic Binding where abstract consumer requests are bound to concrete service instances at runtime. What is clear from existing research is that there exist sever...
Conference Paper
Full-text available
Grid and cloud computing have changed the IT landscape in the way we access and manage IT infrastructures. Both technologies provide easy-to-use and on-demand access to large-scale infrastructures. Grid and cloud computing are major research areas with strong involvement from both academia and industry. Although significant progress has been made i...
Article
Service Level Agreements in Grids improve upon the Best Effort Approach which provides no guarantees for provision of any Quality of Service (QoS) between the End User and the Resource Provider. Risk Assessment in Grids improves upon SLA by provision of Risk information to resource provider. Most of the previous studies of Risk Assessment in Grids...
Conference Paper
Full-text available
Cloud transformations require dynamic redistribution of resources across cloud infrastructure. From a legal perspective this movement of data from one data processor to another without the explicit consent of the data subject is a threat to data privacy. Levels of assurance and accountability have to be provided from the cloud infrastructure provid...
Article
Simulations of mobile ad-hoc, sensor, and mesh networks strongly rely on mobility models because they have a major influence on the performance of protocols. Results obtained with an unrealistic model may not reflect the true performance of protocols, applications and algorithms in real environments. In this paper, we present a mobility model for s...
Article
Large-scale data processing systems frequently require users to make timely and high-value business decisions based upon information that is received from a variety of heterogeneous sources. Such heterogeneity is especially true of service-oriented systems, which are often dynamic in nature and composed of multiple interacting services. However, in...
Chapter
Cloud Computing continues to be a rapidly evolving and prevalent paradigm where Quality of Service (QoS) has a pivotal role to play in guaranteeing performance and provisioning of resources on-demand in a timely fashion. Improvements to the performance of Cloud technology ensure provider profitability and an increased number of applications that ca...
Chapter
We demonstrate a Grid broker's job submission system and its selection process for finding the provider that is most likely to be able to complete work on time and on budget. We compare several traditional site selection mechanisms with an economic and Quality of Service (QoS) oriented approach. We show how a greater profit and QoS can be achieved...
Conference Paper
Full-text available
Increasing emphasis in data protection legislation on the provision of user consent and privacy protection poses a challenge to automated Cloud Computing applications.. Here, the infrastructure is removed from the user and therefore no direct link for consent or user control exists. In such environments assurance and best effort from the Cloud Prov...
Conference Paper
We demonstrate a Grid broker's job submission system and its selection process for finding the provider that is most likely to be able to complete work on time and on budget. We compare several traditional site selection mechanisms with an economic and Quality of Service (QoS) oriented approach. We show how a greater profit and QoS can be achieved...