Stephen Gilmore

Evaluating the Performance of Skeleton-Based High Level Parallel Programs

We show in this paper how to evaluate the performance of skeleton-based high level parallel programs. Since many applications fol- low some commonly used algorithmic skeletons, we identify such skele- tons and model them with process algebra in order to get relevant in- formation about the performance of the application, and be able to take some good scheduling decisions. This concept is illustrated through the case study of the Pipeline skeleton, and a tool which generates auto- matically a set of models and solves them is presented. Some numerical results are provided, proving the efficiency of this approach.

Combining measurement and stochastic modelling to enhance scheduling decisions for a parallel mean value analysis algorithm

In this paper we apply the high-level modelling language PEPA to the performance analysis of a parallel program with a pipeline skeleton which computes the Mean Value Analysis (MVA) algorithm for queueing networks.

Mobile resource guarantees for smart devices

We present the Mobile Resource Guarantees framework: a system for ensuring that downloaded programs are free from run-time violations of resource bounds. Certificates are attached to code in the form of efficiently checkable proofs of resource bounds; in contrast to cryptographic certificates of code origin, these are independent of trust networks. A novel programming language with resource constraints encoded in function types is used to streamline the generation of proofs of resource usage.

Flexible skeletal programming with eskel

We present an overview of eSkel, a library for skeletal parallel programming. eSkel aims to maximise the conceptual flexibility afforded by its component skeletons and to facilitate dynamic selection of skeleton compositions. We present simple examples which illustrate these properties, and discuss the implementation challenges which the model poses.

PEPA Nets: A Structured Performance Modelling Formalism

In this paper we describe a formalism which uses the stochastic process algebra PEPA as the inscription language for labelled stochastic Petri nets. Viewed in another way, the net is used to provide a structure for combining related PEPA systems. The combined modelling language naturally represents such applications as mobile code systems where the PEPA terms are used to model the program code which moves between network hosts (the places in the net). We describe the implementation of a tool to support this modelling formalism and apply this to model a peer-to-peer filestore.

An efficient algorithm for aggregating PEPA models

Performance Evaluation Process Algebra (PEPA) is a formal language for performance modeling based on process algebra. It has previously been shown that, by using the process algebra apparatus, compact performance models can be derived which retain the essential behavioral characteristics of the modeled system. However, no efficient algorithm for this derivation was given. We present an efficient algorithm which recognizes and takes advantage of symmetries within the model and avoids unnecessary computation. The algorithm is illustrated by a multiprocessor example.

PEPA nets: a structured performance modelling formalism

In this paper we describe a formalism which uses the stochastic process algebra PEPA as the inscription language for labelled stochastic Petri nets. Viewed in another way, the net is used to provide a structure for linking related PEPA systems. The combined modelling language naturally represents such applications as mobile code systems where the PEPA terms are used to model the program code which moves between network hosts (the places in the net). We describe, the implementation of a tool to support this modelling formalism and apply this to model a hierarchical cellular network.

Derivation of passage-time densities in PEPA models using ipc: the imperial PEPA compiler

A technique for defining and extracting passage-time densities from high-level stochastic process algebra models is presented. Our high-level formalism is PEPA, a popular Markovian process algebra for expressing compositional performance models. We introduce ipc, a tool which can process PEPA-specified passage-time densities and models by compiling the PEPA model and passage specification into the DNAmaca formalism. DNAmaca is an established modelling language for the low-level specification of very large Markov and semiMarkov chains. We provide performance results for ipc/DNAmaca and comparisons with another tool which supports PEPA, PRISM. Finally, we generate passage-time densities and quantiles for a case study of a high-availability Web server.

Stochastic Process Algebras

In this paper we report on progress in the use of stochastic process algebras for representing systems which contain many replications of components such as clients, servers and devices. Such systems have traditionally been difficult to analyse even when using high-level models because of the need to represent the vast range of their potential behaviour. Models of concurrent systems with many components very quickly exceed the storage capacity of computing devices even when efficient data structures are used to minimize the cost of representing each state. Here, we show how population-based models that make use of a continuous approximation of the discrete behaviour can be used to efficiently analyse the temporal behaviour of very large systems via their collective dynamics. This approach enables modellers to study problems that cannot be tackled with traditional discrete-state techniques such as continuous-time Markov chains.

Analysing UML 2.0 activity diagrams in the software performance engineering process

In this paper we present an original method of analysing the newly-revised UML2.0 activity diagrams. Our analysis method builds on our formal interpretation of these diagrams with respect to the UML2.0 standard. The mapping into another formalism is the first stage of a refinement process which ultimately delivers derived analytical results on the model. This process highlights latent performance problems hidden in the high-level design, allowing software developers to fix these design flaws before they are concretised in implementation code. We exercise our analysis approach on a substantial example of modelling a multi-player distributed role-playing game.