Yvonne Coady

Using aspectC to improve the modularity of path-specific customization in operating system code

Layered architecture in operating system code is often compromised by execution path-specific customizations such as prefetching, page replacement and scheduling strategies. Path-specific customizations are difficult to modularize in a layered architecture because they involve dynamic context passing and layer violations. Effectively they are vertically integrated slices through the layers. An initial experiment using an aspect-oriented programming language to refactor prefetching in the FreeBSD operating system kernal shows significant benefits, including easy (un)pluggability of prefetching modes, independent development of prefetching modes, and overall improved comprehensibility.

Dynamic Resource Allocation in Computing Clouds Using Distributed Multiple Criteria Decision Analysis

In computing clouds, it is desirable to avoid wasting resources as a result of under-utilization and to avoid lengthy response times as a result of over-utilization. In this paper, we propose a new approach for dynamic autonomous resource management in computing clouds. The main contribution of this work is two-fold. First, we adopt a distributed architecture where resource management is decomposed into independent tasks, each of which is performed by Autonomous Node Agents that are tightly coupled with the physical machines in a data center. Second, the Autonomous Node Agents carry out configurations in parallel through Multiple Criteria Decision Analysis using the PROMETHEE method. Simulation results show that the proposed approach is promising in terms of scalability, feasibility and flexibility.

Back to the future: a retroactive study of aspect evolution in operating system code

The FreeBSD operating system more than doubled in size between version 2 and version 4. Many changes to primary modularity are easy to spot at a high-leveL For example, new device drivers account for 38% of the growth. Not surprisingly, changes to crosscutting concerns are more difficult to track. In order to better understand how an aspect-oriented implementation would have fared during this evolution, we introduced several aspects to version 2 code, and then rolled them forward into their subsequent incarnations in versions 3 and 4 respectively. This paper describes the impact evolution had on these concerns, and provides a comparative analysis of the changes required to evolve the tangled versus aspect-oriented implementations.Our results show that for the concerns we chose, the aspect-oriented implementation facilitated evolution in four key ways: (1) changes were better localized, (2) configurability was more explicit, (3) redundancy was reduced, and (4) extensibility aligned with an aspect was more modular. Additionally, we found that the aspect-oriented implementation had negligible impact on performance.

C-CLR: a tool for navigating highly configurable system software

In order to accommodate the spectrum of configuration options currently required for competitive system infrastructures, many systems leverage heavy usage of C preprocessor controlled conditional compilation. In herent costs associated with this heavy preprocessor usage include both the impaired readability of the base system, and the reduced reusability of the configuration code. Our proposed solution, C-CLR, allows developers to sift through views of a system based on configuration options. Configuration-specific views improve readability of the system as a whole by including only relevant code. They also support reusability by aiding aspect mining through easy navigation to relevant configuration options, and automated identification of equivalent blocks of code within conditionally compiled segments.

Maitland: Lighter-Weight VM Introspection to Support Cyber-security in the Cloud

Despite defensive advances, malicious software (malware) remains an ever present cyber-security threat. Cloud environments are far from malware immune, in that: i) they innately support the execution of remotely supplied code, and ii) escaping their virtual machine (VM) confines has proven relatively easy to achieve in practice. The growing interest in clouds by industries and governments is also creating a core need to be able to formally address cloud security and privacy issues. VM introspection provides one of the core cyber-security tools for analyzing the run-time behaviors of code. Traditionally, introspection approaches have required close integration with the underlying hypervisors and substantial re-engineering when OS updates and patches are applied. Such heavy-weight introspection techniques, therefore, are too invasive to fit well within modern commercial clouds. Instead, lighter-weight introspection techniques are required that provide the same levels of within-VM observability but without the tight hypervisor and OS patch-level integration. This work introduces Maitland as a prototype proof-of-concept implementation a lighter-weight introspection tool, which exploits paravirtualization to meet these end-goals. The work assesses Maitlands performance, highlights its use to perform packer-independent malware detection, and assesses whether, with further optimizations, Maitland could provide a viable approach for introspection in commercial clouds.

Structuring operating system aspects: using AOP to improve OS structure modularity

Key elements of operating systems crosscut – their implementation is inherently coupled with several layers of the system. Prefetching, for example, is a critical architectural performance optimization that amortizes the cost of going to disk by predicting and retrieving additional data with each explicit disk request. The implementation of prefetching, however, is tightly coupled with both high-level context of the request source and low-level costs of additional retrieval. In a traditional OS implementation, small clusters of customized prefetching code appear at both high and low levels along most execution paths that involve going to disk. This makes prefetching difficult to reason about and change, and interferes with the clarity of the primary functionality within which prefetching is embedded.

Sustainable system infrastructure and big bang evolution: can aspects keep pace?

Realistically, many rapidly evolving systems eventually require extensive restructuring in order to effectively support further evolution. Not surprisingly, these overhauls reverberate throughout the system. Though several studies have shown the benefits of aspect-oriented programming (AOP) from the point of view of the modularization and evolution of crosscutting concerns, the question remains as to how well aspects fare when the code that is crosscut undergoes extensive restructuring. That is, when evolution is a big bang, can aspects keep pace? The case study presented here considers several categories of aspects – design invariants, dynamic analysis tools, and domain specific design patterns – and shows the concrete ways in which aspects had positive, negative and neutral impact during the restructuring of the memory management subsystem of a virtual machine. Compared with best efforts in a hierarchical decomposition coupled with a preprocessor, aspects fared better than the original implementation in two out of four aspects, and no worse in the remaining two aspects.

Distributed Cloud Computing: Applications, Status Quo, and Challenges

A distributed cloud connecting multiple, geographically distributed and smaller datacenters, can be an attractive alternative to todays massive, centralized datacenters. A distributed cloud can reduce communication overheads, costs, and latencies by o ering nearby computation and storage resources. Better data locality can also improve privacy. In this paper, we revisit the vision of distributed cloud computing, and identify di erent use cases as well as research challenges. This article is based on the Dagstuhl Seminar on Distributed Cloud Computing, which took place in February 2015 at Schloss Dagstuhl.

Using embedded network processors to implement global memory management in a workstation cluster

Advances in network technology continue to improve the communication performance of workstation and PC clusters, making high-performance workstation-cluster computing increasingly viable. These hardware advances, however, are taxing traditional host-software network protocols to breaking point. A modern gigabit network can swamp a hosts IO bus and processor, limiting communication performance and slowing computation unacceptably. Fortunately, host-programmable network processors used by these networks present a potential solution. Offloading selected host processing to these embedded network processors lowers host overhead and improves latency. This paper examines the use of embedded network processors to improve the performance of workstation-cluster global memory management. We have implemented a revised version of the GMS global memory system that eliminates host overhead by as much as 29% on active nodes and improves page fault latency by as much as 39%.

Disentangling virtual machine architecture

Virtual machine (VM) implementations are made of intricately intertwined subsystems, interacting largely through implicit dependencies. As the degree of crosscutting present in VMs is very high, VM implementations exhibit significant internal complexity. This study proposes an architecture approach for VMs that regards a VM as a composite of service modules coordinated through explicit bidirectional interfaces. Aspect-oriented programming techniques are used to establish these interfaces, to coordinate module interaction, and to declaratively express concrete VM architectures. A VM architecture description language is presented in a case study, illustrating the application of the proposed architectural principles.