CPU Scheduling Research Articles

Evaluation of a CPU Scheduling Mechanism for Multimedia Systems

Evaluation of a CPU Scheduling Mechanism for Multimedia Systems

The EOS laboratory environment for a course in operating systems

This paper describes a laboratory environment for teaching operating systems. The EOS (Exploratory Operating Systems) lab was developed with a National Science Foundation ILI grant to be used in conjunction with a traditional operating systems (OS) course. The main goal of the EOS project was to improve the teaching of operating system principles without the necessity of a special purpose laboratory and the addition to the curriculum of a second course in OS. The EOS labs are summarized and a CPU scheduling lab is described in some detail. A standardized testing instrument was used to compare class performance before and after adding the lab to the OS course. Preliminary results show an improvement attributable to the EOS laboratory. The author's experience in building a workstation laboratory from an externally funded grant is described.

Paging tradeoffs in distributed-shared-memory multiprocessors

Massively parallel processors have begun using commodity operating systems that support demand-paged virtual memory. To evaluate the utility of virtual memory, we measured the behavior of seven shared-memory parallel application programs on a simulated distributed-shared-memory machine. Our results (1) confirm the importance of gang CPU scheduling, (2) show that a page-faulting processor should spin rather than invoke a parallel context switch, (3) show that our parallel programs frequently touch most of their data, and (4) indicate that memory, not just CPUs, must be “gang scheduled.” Overall, our experiments demonstrate that demand paging has limited value on current parallel machines because of the applications' synchronization and memory reference patterns and the machines' high page-fault and parallel context-switch overheads.

Research issues in real-time database systems: Survey paper

Today's real-time systems are characterized by managing large volumes of data. Efficient database management algorithms for accessing and manipulating data are required to satisfy timing constraints of supported applications. Real-time database systems involve a new research area investigating possible ways of applying database systems technology to real-time systems. Management of real-time information through a database system requires the integration of concepts from both real-time systems and database systems. Some new criteria need to be developed to involve timing constraints of real-time applications in many database systems design issues, such as transaction/query processing, data buffering, CPU, and IO scheduling. In this paper, a basic understanding of the issues in real-time database systems is provided and the research efforts in this area are introduced. Different approaches to various problems of real-time database systems are briefly described, and possible future research directions are discussed.

The design of a QoS-controlled ATM-based communications system in Chorus

We describe the design of an application platform able to run distributed real-time and multimedia applications alongside conventional UNIX programs. The platform is embedded in a microkernel/PC environment and supported by an ATM-based, QoS-driven communications stack. In particular, we focus on resource-management aspects of the design and deal with CPU scheduling, network resource-management and memory-management issues. An architecture is presented that guarantees QoS levels of both communications and processing with varying degrees of commitment as specified by user-level QoS parameters. The architecture uses admission tests to determine whether or not new activities can be accepted and includes modules to translate user-level QoS parameters into representations usable by the scheduling, network, and memory-management subsystems. >

The system architecture of the Heidelberg transport system

HeiTS, the Heidelberg Transport System, is designed for communication of continuous-media data. The purpose of HeiTS is the exchange of digital audio and video with quality of service guarantees. The system environment of HeiTS has to coordinate real-time and non-real-time functions. Most parts of HeiTS run in user space; it uses some kernel-based mechanisms such as a real-time CPU scheduler and device drivers. On top of HeiTS exists a control system which allows for the construction of applications controlling continuous-media streams. This paper describes the architecture of HeiTS and the mechanisms of its system environment we have implemented on AIX and OS/2 platforms.

Metascheduling for continuous media

Next-generation distributed systems will supportcontinuous media(digital audio and video) in the same framework as other data. Many applications that use continuous media need guaranteed end-to-end performance (bounds on throughput and delay). To reliably support these requirements, system components such as CPU schedulers, networks, and file systems must offer performance guarantees. Ametaschedulercoordinates these components, negotiating end-to-end guarantees on behalf of clients. TheCM-resource model, described in this paper, provides a basis for such a metascheduler. It defines a workload parameterization, an abstract interface to resources, and an algorithm for reserving multiple resources. The model uses an economic approach to dividing end-to-end delay, and it allows system components to “work ahead,” improving the performance of nonreal-time workload.

More Experience with MINIX in an Operating Systems Lab

In operating systems classes students study the theory, concepts, and mechanisms of operating systems: system calls, layered design, the client‐server model, processes, interprocess communication, CPU scheduling, deadlock, input and output, device drivers, memory management, file systems, protection, etc. Their understanding of these concepts will be enhanced if they are given the opportunity to examine the internal operation and source code of an actual operating system and see how the various concepts and features studied are implemented. By modifying the source code to change the behavior of the operating system or introduce new features, students can further enhance their understanding and gain valuable practical experience. This article describes the use of the Apple Macintosh version of MINIX, a UNIX look‐alike operating system available in source form, in an operating systems workshop course. The use of the Macintosh version is compared to the IBM PC version. What the students learned from the work...

A CPU scheduling simulation from structured programming to object-oriented design

Object-oriented programming has become increasingly popular in the past few years. This paper presents a cpu scheduling simulation project that we feel can convince students of the benefits of object-oriented design and spur their interest. We will first describe the project and discuss its solutions in three levels of abstraction: structure programming using Pascal, object-based programming using Ada, and object-oriented programming using C++. We will present our experiences in this assignment and explain why the object-oriented design is the best approach. This paper is intended to serve as a case study in an object-oriented language course or a programming languages course.

Reflection facilities and realistic programming

We propose a new reflection model called 2-dimensional hierarchical reflection . The model naturally describes reflective facilities which enable us to change the language semantics as well as the underlying environment, i.e., memory management and cpu scheduling. The concurrent object-oriented programming language called AL-1 has been designed based on the model. The language is an adaptable/extensible system in the sense that the system's bevavior is dynamically changed by the way of reflection. In order to demonstrate how the language is adapted in user's demand, the typical reflective programming in the language is presented.

A trace-driven simulation study of dynamic load balancing

A trace-driven simulation study of dynamic load balancing in homogeneous distributed systems supporting broadcasting is presented. Information about job CPU and input/output (I/O) demands collected from production systems is used as input to a simulation model that includes a representative CPU scheduling policy and considers the message exchange and job transfer cost explicitly. Seven load-balancing algorithms are simulated and their performances compared. Load balancing is capable of significantly reducing the mean and standard deviation of job response times, especially under heavy load, and for jobs with high resource demands. Algorithms based on periodic or nonperiodic load information exchange provide similar performance, and, among the periodic policies, the algorithms that use a distinguished agent to collect and distribute load information cut down the overhead and scale better. With initial job placements only, source initiative algorithms were found to perform better than server initiative algorithms. The performances of all hosts, even those originally with light loads, are generally improved by load balancing. >

A trace-driven simulation study of dynamic load balancing

A trace-driven simulation study of dynamic load balancing in homogeneous distributed systems supporting broadcasting is presented. Information about job CPU and input/output (I/O) demands collected from production systems is used as input to a simulation model that includes a representative CPU scheduling policy and considers the message exchange and job transfer cost explicitly. Seven load-balancing algorithms are simulated and their performances compared. Load balancing is capable of significantly reducing the mean and standard deviation of job response times, especially under heavy load, and for jobs with high resource demands. Algorithms based on periodic or nonperiodic load information exchange provide similar performance, and, among the periodic policies, the algorithms that use a distinguished agent to collect and distribute load information cut down the overhead and scale better. With initial job placements only, source initiative algorithms were found to perform better than server initiative algorithms. The performances of all hosts, even those originally with light loads, are generally improved by load balancing. >

Optimality of scheduling policy for processing a job stream

It has been claimed on the basis of empirical studies that a CPU scheduling policy, whereby I/Obound jobs are given preemptive priority over CPU-bound jobs, produces the highest overall CPU utilization of multiprogrammed computer systems. However, a theoretical result has shown that the CPU utilization is independent of CPU scheduling in a finite-source queuing model of multiprogrammed systems. This paper aims at resolving this seeming conflict and gaining some insight into CPU scheduling by analyzing a Markovian model of job-stream processing. The model studied consists of an infinite backlog of jobs of two classes (a job stream} and a multiple-resource system (the model of a multiprogrammed system which processes the job stream}; the system consists of a cyclic queue of two nodes--a single (CPU) server and an infinite (I/O) server. The system contains a fixed number of jobs concurrently; the values of parameters describing each job class are distinct except for the mean I/O service time. The following result is obtained under the near-complete decomposability of the model: The maximum overall CPU server utilization (and the maximum throughput) is achieved by scheduling policy whereby jobs of the class having a shorter mean CPU service time are given preemptive priority over others at the CPU server, although the CPU server utilization is independent of CPU scheduling so long as the set of jobs in the system remains fixed.

A simulation approach to the comparative analysis of various job scheduling methods

A simulation approach to the comparative analysis of different job scheduling methods with regard to CPU efficiency, the job throughput, and the job waiting time is presented. The job-processing simulation model is implemented in PL/1. In order to consider several possible dynamic situations for the job-scheduling methods, we simulated the job starting from its entry at the RJE (remote job entry) terminal until the job leaves the system, which includes an IBM 370/158 and AMDAHL 470 V/7. In particular, a Fourier series is used to predict the required CPU time for the job and to assign dynamically the internal priority for CPU scheduling. A detailed summary of conclusions that can be drawn from the simulation is given.

Trace-driven modeling and analysis of CPU scheduling in a multiprogramming system

Microscopic level job stream data obtained in a production environment by an event-driven software probe is used to drive a model of a multiprogramming computer system. The CPU scheduling algorithm of the model is systematically varied. This technique, called trace-driven modeling, provides an accurate replica of a production environment for the testing of variations in the system. At the same time alterations in scheduling methods can be easily carried out in a controlled way with cause and effects relationships being isolated. The scheduling methods tested included the best possible and worst possible methods, the traditional methods of multiprogramming theory, round-robin, first-come-first-served, etc., and dynamic predictors. The relative and absolute performances of these scheduling methods are given. It is concluded that a successful CPU scheduling method must be preemptive and must prevent a given job from holding the CPU for too long a period.

Demultiplexing Considerations for Statistical Multiplexors

Demultiplexing serves as an important function for statistical multiplexors. Its purpose is to reassemble the received message and distribute it to the appropriate destination. An important cost consideration for this function is the size of the buffer necessary to meet a specified overflow service requirement. The demultiplexing buffer can be modeled as a finite waiting room queueing model with batch Poisson arrivals and multiple distinct constant servers. Stimulation is used to study buffer behavior for traffic arriving at the buffer according to the uniform, linear, step, and geometric destination functions. The relationships among buffer overflow probability, buffer size, traffic intensity, average message length, and message destination are presented in graphs to provide a guide in the design of demultiplexing buffers. Simulation results reveal that buffer input messages that have short average message lengths and uniform traffic destinations yield the best buffer behavior. Thus, in planning the CPU scheduling algorithm and in selecting the demultiplexing output rates, the designing of a computer communications system that uses the statistical multiplexing technique should also consider the output statistics needed to achieve optimal demultiplexing performance.

An Unclever Time-Sharing System

This paper describes the internal structure of a time-sharing system in some detail. This system is dedicated to providing remote access, and has a simple file structure. It is intended for use in a university type environment where there are many short jobs that will profit from one- or two-second turnaround. Despite its simplicity, this system can serve as a useful introduction to the problems encountered by the designers of any time-sharing system. Included are a discussion of the command language, the hardware organization toward which the design is oriented, the general internal organization, the command sequences, the CPU scheduler, handling of interrupts, the assignment of core space, execution and control of the user's program, backup storage management, and the handling of errors.