# Performability

**Performability** is that property of a computer system such that it delivers performance required by the **service**, as described by **QoS** (quality of service) measures.

### [Meyer-1980 (doi) .]

John F. Meyer,

“On Evaluating the Performability of Degradable Computing Systems ”,

*IEEE Transactions on Computers*, vol.29, #8, Aug. 1980, pp. 720–731

**ResiliNets Keywords: ** performability

**Keywords:** degradable computing systems, fault-tolerant computing, hierarchical modeling, performability evaluation, performance evaluation, reliability evaluation

**Abstract:** “If the performance of a computing system is "degradable," performance and reliability issues must be dealt with simultaneously in the process of evaluating system effectiveness. For this purpose, a unified measure, called "performability," is introduced and the foundations of performability modeling and evaluation are established. A critical step in the modeling process is the introduction of a "capability function" which relates low-level system behavior to user-oriented performance levels. A hierarchical modeling scheme is used to formulate the capability function and capability is used, in turn, to evaluate performability. These techniques are then illustrated for a specific application: the performability evaluation of an aircraft computer in the environment of an air transport mission.”

**Notes:**

### [Meyer-1992 (doi) .]

John F. Meyer,

“Performability: A Retrospective and Some Pointers to the Future”,

*Performance Evaluation*, Elsevier, vol.14, #3-4, February 1992, pp. 139–156

**ResiliNets Keywords: ** performability

**Keywords:** performability, degradable performance, dependability, fault tolerance, model-based evaluation

**Abstract:** “As computing and communication systems become physically and logically more complex, their evaluation calls for continued innovation with regard to measure definition, model construction/solution, and tool development. In particular, the performance of such systems is often degradable, i.e., internal or external faults can reduce the quality of a delivered service even though that service, according to its specification, remains proper (failure-free). The need to accommodate this property, using model-based evaluation methods, was the raison d'être for the concept of performability. To set the stage for additional progress in its development, we present a retrospective of associated theory, techniques, and applications resulting from work in this area over the past decade and a half. Based on what has been learned, some pointers are made to future directions which might further enhance the effectiveness of these methods and broaden their scope of applicability.”

**Notes:**

### [Meyer-1995 (doi) .]

John F. Meyer,

“Performability evaluation: where it is and what lies ahead”,

*IEEE IPDS*, April 1995, pp. 334–343

**ResiliNets Keywords: ** performability

**Keywords:** design applicability , performability evaluation , performance-dependability measures

**Abstract:** “The concept of performability emerged from a need to assess a system's ability to perform when performance degrades as a consequence of faults. After almost 20 years of effort concerning its theory, techniques, and applications, performability evaluation is currently well understood by the many people responsible for its development. On the other hand, the utility of combined performance-dependability measures has yet to be appreciably recognized by the designers of contemporary computer systems. Following a review of what performability means, we discuss its present state with respect to both scientific and engineering contributions. In view of current practice and the potential design applicability of performability evaluation, we then point to some advances that are called for if this potential is indeed to be realized.”

**Notes:**

### [Edwards-Rees 1994 .]

Nigel Edwards and Owen Rees,

*A Model for Failures in Dependable Systems*,

ANSA Technical Report, March, 1994

**Abstract:** “This document describes a model for failures in dependable systems. A general failure model is
described in terms of a system consisting of interacting components. This model is then applied
to an object-based interaction model. The model is based on events which occur with some value at some time. Components in the system observe events and have expectations which define regions in a value, time space. A failure is detected when what is observed does not match what is expected. The concepts in the model can be used to analyse a given configuration of engineering mechanisms, application components and infrastructure to determine what failures can and cannot be tolerated by this configuration. This can then be mapped onto an application-level statement: what failures the applications can and cannot tolerate. The intention is that the model should provide the underlying framework for further work on dependable distributed computing. Some familiarity with basic principles of object-based distributed computing is assumed.”

**ResiliNets Keywords: ** dependability, survivability, performability

**Keywords:** Failure model, expectations

**Notes:** Defines expectations in time × value space, in which dependability and performability are measured as occurrences with respect to expectations.

### [Meyer-1976 (doi) .]

John F. Meyer,

“Computation-Based Reliability Analysis”,

*IEEE Transactions on Computers*, vol.C-25, #6, Aug. 1976, pp. 578–584

**ResiliNets Keywords: ** performability

**Keywords:** Error tolerance, fault tolerance, reliability analysis, reliability modeling

**Abstract:** “A reliability analysis method for computing systems is considered in which the underlying criteria for "success" are based on the computations the system must perform in the use environment. Beginning with a general model of a "computer with faults," intermediate concepts of a "tolerance relation" and an "environment space" are introduced which account for the computational needs of the user and the probabilistic nature of the use environment. These concepts are then incorporated to obtain a precisely defined class of computation-based reliability measures. Formulation of a particular measure is illustrated and results, applying this measure, are compared with those of a typical structure-based analysis.”

**Notes:**

### [Borgerson-Freitas-1975 (doi) .]

B.R. Borgerson, and R.F. Freitas,

“A Reliability Model for Gracefully Degrading and Standby-Sparing Systems”,

*IEEE Transactions on Computers*, vol.C-24, #5, May 1975, pp. 517–525

**ResiliNets Keywords: ** performability

**Keywords:** Fault tolerance, gracefully degrading, PRIME, reliability, resource exhaustion, solitary faults, space-domain multiple faults, standby sparing, time-domain multiple faults

**Abstract:** “A model for analyzing the reliability of gracefully degrading and standby-sparing computer systems is developed. The basis of the model is the identification of four distinct causes of crashes: time-domain multiple faults, resource exhaustion, space-domain multiple faults, and solitary faults. Expressions are developed for each of these crash-causing mechanisms and for their interrelationship. The model is then demonstrated by using it to analyze the reliability of a gracefully degrading computer system called PRIME.”

**Notes:**

### [Huslende-1981 (doi) .]

Ragnar Huslende,

“A combined evaluation of performance and reliability for degradable systems”,

*ACM SIGMETRICS*, 1981, pp. 157–164

**ResiliNets Keywords: ** performability

**Keywords:** Performance, Reliability

**Abstract:** “ As the field of fault-tolerant computing is maturing and results from this field are taken into practical use the effects of a failure in a computer system need not be catastrophic. With good fault-detection mechanisms it is now possible to cover a very high percentage of all the possible failures that can occur. Once a fault is detected, systems are designed to reconfigure and proceed either with full or degraded performance depending on how much redundancy is built into the system. It should be noted that one particular failure may have different effects depending on the circumstances and the time at which it occurs. Today we see that large numbers of resources are being tied together in complex computer systems, either locally or in geographically distributed systems and networks. In such systems it is obviously very undesirable that the failure of one element can bring the entire system down. On the other hand one can usually not afford to design the system with sufficient redundancy to mask the effect of all failures immediately. ”

**Notes:**

### [Wu-1982 (doi) .]

L.T. Wu,

“Operational models for the evaluation of degradable computing systems”,

*ACM SIGMETRICS*, 1982, pp. 179–185

**ResiliNets Keywords: ** performability

**Keywords:**

**Abstract:** “Recent advances in multiprocessor technology have established the need for unified methods to evaluate computing systems performance and reliability. In response to this modeling need, this paper considers a general modeling framework which permits the modeling, analysis and evaluation of degradable computing systems. Within this framework, a simple and useful user-oriented performance variable is identified and shown to be a proper generalization of the traditional notions of system performance and reliability.

The modeling and evaluation methods considered in this paper provide a relatively straightforward approach for integrating reliability and availability measures with performance measures. The hierarchical decomposition approach permits the modeling and evaluation of a computing system's subsystems (e.g., hardware, software, peripherals, interfaces, user demand systems) as a whole rather than the traditional methods of evaluating these subsystems independently. Accordingly, it becomes possible to evaluate the performance of the system software and the reliability of the system hardware simultaneously in order to measure the effectiveness of the system design. Since the performance variable introduced permits the characterization of the system performance according to the user's view of the systems, the results obtained represent more accurate assessments of the system's ability to perform than the existing performance or reliability measures.”

**Notes:**

### [Losq-1977 .]

J. Losq,

“Effects of Failures on Gracefully Degradable Systems”,

*7th Fault-Tolerant Computing Symposium*, 1977, pp. 29–34

**ResiliNets Keywords: ** performability

**Keywords:**

**Abstract:**

**Notes:**

### [Ng-Avizienis-1977 .]

YW Ng and A. Avizienis,

“A Reliability Model for Gracefully Degrading and Repairable Fault-tolerant Systems”,

*7th International Symposium on Fault-Tolerant Computing*, 1977

**ResiliNets Keywords: ** performability

**Keywords:**

**Abstract:**

**Notes:**

### [Beaudry-1977 (doi) .]

M.D Beaudry,

“Performance-Related Reliability Measures for Computing Systems”,

*IEEE Transactions on Computers*, Vol 27, pp 540–547, 1978

**ResiliNets Keywords: ** performability

**Keywords:** Computer performance, computer reliability, graceful degradation

**Abstract:** “We have developed measures which reflect the interaction between the reliability and the performance characteristics of computing systems. These measures can be used to evaluate traditional computer architectures, such as uniprocessors and standby redundant systems; gracefully degrading systems, such as multiprocessors, which can react to a detected failure by reconfiguring to a state with a decreased level of performance; and distributed systems. This analysis method, which provides quantitative information about the tradeoffs between reliability and performance, is demonstrated in several examples.”

**Notes:**

### [Liew-Lu-1992 (doi) .]

Soung C. Liew and Kevin W. Lu,

“A Framework for Network Survivability Characterization”,

*IEEE International Conference on Communications (ICC 92)*, pp 405–410, 1992

**ResiliNets Keywords: ** performability

**Keywords:**

**Abstract:**“The authors formulate a general framework that includes and extends the existing definitions for network survivability. Based on this framework, network survivability is characterized by a survivability function rather than a single-value survivability measure, and various quantities of interest can be derived from the function. Examples are the expected survivability, the worst-case survivability, the r-percentile survivability, and the probability of zero survivability. The survivability function is especially useful for the study of large-scale disasters. For illustration, the authors derive the survivability function in closed form for a simple ring network under link failures. They also discuss the general procedure for finding survivability functions for complex networks, and show that the survivability function reveals useful information about a network. This framework provides a unified and practical approach to analyzing and designing highly survivable communications networks.”

**Notes:**

### [Liew-Lu-1994 (doi) .]

Soung C. Liew and Kevin W. Lu,

“A framework for characterizing disaster-based network survivability”,

*IEEE International Conference on Communications (ICC 92)*, pp 405–410, 1992

**ResiliNets Keywords: ** performability

**Keywords:**

**Abstract:**“This paper formulates a general framework that includes and extends the existing definitions for network survivability. Based on this framework, network survivability is characterized by a survivability function rather than a single-value survivability measure, and various quantities of interest can be derived from the function. Examples are the expected survivability, the worst-case survivability, the r-percentile survivability, and the probability of zero survivability. The survivability function is especially useful for the study of large-scale disasters. For illustration, the authors derive the survivability function in closed form for a simple ring network under link failures. They also discuss the general procedure for finding survivability functions for complex networks, and show that the survivability function reveals useful information about a network. This framework provides a unified and practical approach to analyzing and designing highly survivable communications networks.”

**Notes:**

### [Meyer-2009 .]

J. F. Meyer,

“Deﬁning and Evaluating Resilience: A Performability Perspective”,

*Proceedings of the International Workshop on Performability Modeling of Computer and Communication Systems(PMCCS)*, 2009

**ResiliNets Keywords: ** performability

**Keywords:**

**Abstract:**“The notion of system “resilience” is receiving increased attention in domains ranging from safety-critical applications to ubiquitous computing. After reviewing how resilience has been deﬁned in these contexts, we discuss roles that performability can play in both its deﬁnition and evaluation.”

**Notes:**

## Entries to Add

[Gay-Ketelsen-1979] (ref [36] in [Meyer-1992])