Dorina C. Petriu

The stochastic rendezvous network model for performance of synchronous client-server-like distributed software

Distributed or parallel software with synchronous communication via rendezvous is found in client-server systems and in proposed open distributed systems, in implementation environments such as Ada, V, remote procedure call systems, in transputer systems, and in specification techniques such as CSP, CCS and LOTOS. The delays induced by rendezvous can cause serious performance problems, which are not easy to estimate using conventional models which focus on hardware contention, or on a restricted view of the parallelism which ignores implementation constraints. Stochastic rendezvous networks are queueing networks of a new type which have been proposed as a modelling framework for these systems. They incorporate the two key phenomena of included service and a second phase of service. This paper extends the model to also incorporate different services or entries associated with each task. Approximations to arrival-instant probabilities are employed with a mean-value analysis framework, to give approximate performance estimates. The method has been applied to moderately large industrial software systems. >

The Future of Software Performance Engineering

Performance is a pervasive quality of software systems; everything affects it, from the software itself to all underlying layers, such as operating system, middleware, hardware, communication networks, etc. Software Performance Engineering encompasses efforts to describe and improve performance, with two distinct approaches: an early-cycle predictive model-based approach, and a late-cycle measurement-based approach. Current progress and future trends within these two approaches are described, with a tendency (and a need) for them to converge, in order to cover the entire development cycle.

Applying the UML Performance Profile: Graph Grammar-Based Derivation of LQN Models from UML Specifications

The Object Management Group (OMG) is in the process of defining a UML Profile for Schedulability, Performance and Time that will enable the construction of models for making quantitative predictions regarding these characteristics. The paper proposes a graph-grammar based method for transforming automatically a UML model annotated with performance information into a Layered Queueing Network (LQN) performance model. The input to our transformation algorithm is an XML file that contains the UML model in XML format according to the standard XMI interface. The output is the corresponding LQN model description file, which can be read directly by existing LQN solvers. The LQN model structure is generated from the high-level software architecture and from deployment diagrams indicating the allocation of software components to hardware devices. The LQN model parameters are obtained from detailed models of key performance scenarios, represented as UML interaction or activity diagrams.

Sensor-based information appliances

Using the existing home infrastructure based on open industry standards, we will be able to integrate the home network with external networks to easily manage home devices, both locally and remotely. The advent of pervasive computing marks an urgent need for a new generation of intelligent sensing agents and information appliances. It will also demand environments for resource management of broad applications involving loosely coupled, event-driven, diverse information appliances. It is suggested that the development of intelligent sensing agents and sensor-based information appliances will spread pervasive technology to a multitude of human activities such as mining and manufacturing, security, transportation, sports, and health care. The topics discussed also include management of heterogeneous functions and networking technologies.

A dependability profile within MARTE

The importance of assessing software non-functional properties (NFP) beside the functional ones is well accepted in the software engineering community. In particular, dependability is a NFP that should be assessed early in the software life-cycle by evaluating the system behaviour under different fault assumptions. Dependability-specific modeling and analysis techniques include for example Failure Mode and Effect Analysis for qualitative evaluation, stochastic Petri nets for quantitative evaluation, and fault trees for both forms of evaluation. Unified Modeling Language (UML) may be specialized for different domains by using the profile mechanism. For example, the MARTE profile extends UML with concepts for modeling and quantitative analysis of real-time and embedded systems (more specifically, for schedulability and performance analysis). This paper proposes to add to MARTE a profile for dependability analysis and modeling (DAM). A case study of an intrusion-tolerant message service will offer insight on how the MARTE-DAM profile can be used to derive a stochastic Petri net model for performance and dependability assessment.

A toolset for performance engineering and software design of client-server systems

Abstract TimeBench/SRVN is a prototype toolset for computer-aided design and performance analysis of software, with an emphasis on distributed client-server systems. The performance behaviour of such systems may defy intuition because it involves factors in the software design (such as the partitioning of the functionality and the frequency with which requests will be made to each server) and in the configuration of the distributed system (including replication of services, the distribution of data, and the speed of network access). The novelty of the tool consists in providing support both for developing design specifications and also for performance analysis. The integrated approach avoids the semantic gap between a designers domain and the performance modeling domain, and assists the designer to explore factors that impact the performance of a design. The performance models are based on the Stochastic Rendezvous Network (SRVN) formalism for client-server systems with synchronous service requests. The distinctive features of SRVNs are nested services (since servers can also act as clients to other servers) and the existence of two or more phases of service (the first executed while the client is blocked, and the others executed in parallel with the client). TimeBench/SRVN is intended as a demonstration of the concept of an integrated designer/performance interface, and as a research environment for fast analytic solvers for the models. Besides a simulation solver, it offers three approximate analytic solvers based on recent research, a Markovian solver, a technique for finding bounds on the throughput without too many assumptions, and a tool for rapidly exploring the space of possible parameter values.

Software Performance Models from System Scenarios in Use Case Maps

Software performance concerns begin at the very outset of a new project. The first definition of a software system may be in the form of Use Cases, which may be elaborated as scenarios: this work creates performance models from scenarios. The Use Case Maps notation captures the causal flow of intended execution in terms of responsibilities, which may be allocated to components, and which are annotated with expected resource demands. The SPT algorithm was developed to transform scenario models into performance models. The UCM2LQN tool implements SPT and converts UCM scenario models to layered queueing performance models, allowing rapid evaluation of an evolving scenario definition. The same reasoning can be applied to other scenario models such as Message Sequence Charts, UML Activity Graphs (or Collaboration Diagrams, or Sequence Diagrams), but UCMs are particularly powerful, in that they can combine interacting scenarios and show scenario interactions. Thus a solution for UCMs can be applied to multiple scenarios defined with other notations.

Architecture-based performance analysis applied to a telecommunication system

Software architecture plays an important role in determining software quality characteristics, such as maintainability, reliability, reusability, and performance. Performance effects of architectural decisions can be evaluated at an early stage by constructing and analyzing quantitative performance models, which capture the interactions between the main components of the system as well as the performance attributes of the components themselves. The paper proposes a systematic approach to building layered queueing network (LQN) performance models from a UML description of the high-level architecture of a system and more exactly from the architectural patterns used for the system. The performance model structure retains a clear relationship with the system architecture, which simplifies the task of converting performance analysis results into conclusions and recommendations related to the software architecture. The proposed approach is applied to a telecommunication product for which an LQN model is built and analyzed. The analysis shows how the performance bottleneck is moving from component to component (hardware or software) under different loads and configurations and exposes some weaknesses in the original software architecture, which prevent the system from using the available processing power at full capacity due to excessive serialization.

XSLT transformation from UML models to LQN performance models

A graph grammar-based transformation of a UML design model into a Layered Queueing Network (LQN) performance model was previously proposed by the authors of this paper. The actual transformation was implemented in two ways: first by using an existing graph-rewriting tool, and secondly through an ad-hoc graph transformation implemented in Java.This paper extends the previous work of the authors by proposing a third approach to implement the UML to LQN transformation by using XSLT. Recommended by the World Wide Web Consortium (W3C) the Extensible Stylesheet Language for Transformations (XSLT) is a flexible language for transforming XML documents into various formats including HTML, XML, text, PDF, etc. The input to our XSLT transformation is an XML file that contains the UML model in XML format according to the standard XML Metadata Interchange (XMI). The output is the corresponding LQN model description file, which can be read directly by existing LQN solvers. The paper compares the relative advantages and disadvantages of the XSLT transformation with the previous approaches proposed by the authors, describes the principles of the XSLT transformation and applies it to a case study.

Annotating UML models with non-functional properties for quantitative analysis

This work is motivated by the recent Request For Proposals issued by OMG for a new UML Profile named “Modeling and Analysis of Real-Time and Embedded systems”. The paper describes first some domain concepts for annotating Non-Functional Properties (NFPs), whose focus is on supporting temporal verification of UML-based models. Particular emphasis is given to schedulability and performance analysis for real-time systems. We discuss next some general requirements for NFP annotations and evaluate how the UML profiles for “Schedulability, Performance, and Time Specification” and for “Modeling Quality of Service and Fault Tolerance Characteristics and Mechanisms”, address these requirements. Last but not least, the paper proposes a preliminary framework for describing NFPs by considering the major requirements previously stated and by analyzing some UML mechanisms to attach NFPs to model elements.