Cooperative & Preemptive Context Switching
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Integrating Preemption Threshold Scheduling and Dynamic Voltage Scaling for Energy Efficient Real-Time Systems
Integrating Preemption Threshold Scheduling and Dynamic Voltage Scaling for Energy Efficient Real-Time Systems Ravindra Jejurikar1 and Rajesh Gupta2 1 Centre for Embedded Computer Systems, University of California Irvine, Irvine CA 92697, USA jeÞÞ@cec׺ÙciºedÙ 2 Department of Computer Science and Engineering, University of California San Diego, La Jolla, CA 92093, USA gÙÔØa@c׺Ùc×dºedÙ Abstract. Preemption threshold scheduling (PTS) enables designing scalable real-time systems. PTS not only decreases the run-time overhead of the system, but can also be used to decrease the number of threads and the memory require- ments of the system. In this paper, we combine preemption threshold scheduling with dynamic voltage scaling to enable energy efficient scheduling in real-time systems. We consider scheduling with task priorities defined by the Earliest Dead- line First (EDF) policy. We present an algorithm to compute threshold preemption levels for tasks with given static slowdown factors. The proposed algorithm im- proves upon known algorithms in terms of time complexity. Experimental results show that preemption threshold scheduling reduces on an average 90% context switches, even in the presence of task slowdown. Further, we describe a dynamic slack reclamation technique that working in conjunction with PTS that yields on an average 10% additional energy savings. 1 Introduction With increasing mobility and proliferation of embedded systems, low power consump- tion is an important aspect of embedded systems design. Generally speaking, the pro- cessor consumes a significant portion of the total energy, primarily due to increased computational demands. Scaling the processor frequency and voltage based on the per- formance requirements can lead to considerable energy savings. -
What Is an Operating System III 2.1 Compnents II an Operating System
Page 1 of 6 What is an Operating System III 2.1 Compnents II An operating system (OS) is software that manages computer hardware and software resources and provides common services for computer programs. The operating system is an essential component of the system software in a computer system. Application programs usually require an operating system to function. Memory management Among other things, a multiprogramming operating system kernel must be responsible for managing all system memory which is currently in use by programs. This ensures that a program does not interfere with memory already in use by another program. Since programs time share, each program must have independent access to memory. Cooperative memory management, used by many early operating systems, assumes that all programs make voluntary use of the kernel's memory manager, and do not exceed their allocated memory. This system of memory management is almost never seen any more, since programs often contain bugs which can cause them to exceed their allocated memory. If a program fails, it may cause memory used by one or more other programs to be affected or overwritten. Malicious programs or viruses may purposefully alter another program's memory, or may affect the operation of the operating system itself. With cooperative memory management, it takes only one misbehaved program to crash the system. Memory protection enables the kernel to limit a process' access to the computer's memory. Various methods of memory protection exist, including memory segmentation and paging. All methods require some level of hardware support (such as the 80286 MMU), which doesn't exist in all computers. -
Chapter 1. Origins of Mac OS X
1 Chapter 1. Origins of Mac OS X "Most ideas come from previous ideas." Alan Curtis Kay The Mac OS X operating system represents a rather successful coming together of paradigms, ideologies, and technologies that have often resisted each other in the past. A good example is the cordial relationship that exists between the command-line and graphical interfaces in Mac OS X. The system is a result of the trials and tribulations of Apple and NeXT, as well as their user and developer communities. Mac OS X exemplifies how a capable system can result from the direct or indirect efforts of corporations, academic and research communities, the Open Source and Free Software movements, and, of course, individuals. Apple has been around since 1976, and many accounts of its history have been told. If the story of Apple as a company is fascinating, so is the technical history of Apple's operating systems. In this chapter,[1] we will trace the history of Mac OS X, discussing several technologies whose confluence eventually led to the modern-day Apple operating system. [1] This book's accompanying web site (www.osxbook.com) provides a more detailed technical history of all of Apple's operating systems. 1 2 2 1 1.1. Apple's Quest for the[2] Operating System [2] Whereas the word "the" is used here to designate prominence and desirability, it is an interesting coincidence that "THE" was the name of a multiprogramming system described by Edsger W. Dijkstra in a 1968 paper. It was March 1988. The Macintosh had been around for four years. -
Mac OS X: an Introduction for Support Providers
Mac OS X: An Introduction for Support Providers Course Information Purpose of Course Mac OS X is the next-generation Macintosh operating system, utilizing a highly robust UNIX core with a brand new simplified user experience. It is the first successful attempt to provide a fully-functional graphical user experience in such an implementation without requiring the user to know or understand UNIX. This course is designed to provide a theoretical foundation for support providers seeking to provide user support for Mac OS X. It assumes the student has performed this role for Mac OS 9, and seeks to ground the student in Mac OS X using Mac OS 9 terms and concepts. Author: Robert Dorsett, manager, AppleCare Product Training & Readiness. Module Length: 2 hours Audience: Phone support, Apple Solutions Experts, Service Providers. Prerequisites: Experience supporting Mac OS 9 Course map: Operating Systems 101 Mac OS 9 and Cooperative Multitasking Mac OS X: Pre-emptive Multitasking and Protected Memory. Mac OS X: Symmetric Multiprocessing Components of Mac OS X The Layered Approach Darwin Core Services Graphics Services Application Environments Aqua Useful Mac OS X Jargon Bundles Frameworks Umbrella Frameworks Mac OS X Installation Initialization Options Installation Options Version 1.0 Copyright © 2001 by Apple Computer, Inc. All Rights Reserved. 1 Startup Keys Mac OS X Setup Assistant Mac OS 9 and Classic Standard Directory Names Quick Answers: Where do my __________ go? More Directory Names A Word on Paths Security UNIX and security Multiple user implementation Root Old Stuff in New Terms INITs in Mac OS X Fonts FKEYs Printing from Mac OS X Disk First Aid and Drive Setup Startup Items Mac OS 9 Control Panels and Functionality mapped to Mac OS X New Stuff to Check Out Review Questions Review Answers Further Reading Change history: 3/19/01: Removed comment about UFS volumes not being selectable by Startup Disk. -
CS 151: Introduction to Computers
Information Technology: Introduction to Computers Handout One Computer Hardware 1. Components a. System board, Main board, Motherboard b. Central Processing Unit (CPU) c. RAM (Random Access Memory) SDRAM. DDR-RAM, RAMBUS d. Expansion cards i. ISA - Industry Standard Architecture ii. PCI - Peripheral Component Interconnect iii. PCMCIA - Personal Computer Memory Card International Association iv. AGP – Accelerated Graphics Port e. Sound f. Network Interface Card (NIC) g. Modem h. Graphics Card (AGP – accelerated graphics port) i. Disk drives (A:\ floppy diskette; B:\ obsolete 5.25” floppy diskette; C:\Internal Hard Disk; D:\CD-ROM, CD-R/RW, DVD-ROM/R/RW (Compact Disk-Read Only Memory) 2. Peripherals a. Monitor b. Printer c. Keyboard d. Mouse e. Joystick f. Scanner g. Web cam Operating system – a collection of files and small programs that enables input and output. The operating system transforms the computer into a productive entity for human use. BIOS (Basic Input Output System) date, time, language, DOS – Disk Operating System Windows (Dual, parallel development for home and industry) Windows 3.1 Windows 3.11 (Windows for Workgroups) Windows 95 Windows N. T. (Network Technology) Windows 98 Windows N. T. 4.0 Windows Me Windows 2000 Windows XP Home Windows XP Professional The Evolution of Windows Early 80's IBM introduced the Personal PC using the Intel 8088 processor and Microsoft's Disk Operating System (DOS). This was a scaled down computer aimed at business which allowed a single user to execute a single program. Many changes have been introduced over the last 20 years to bring us to where we are now. -
Real-Time Operating Systems with Example PICOS18
Real-Time Operating Systems With Example PICOS18 Sebastian Fischmeister 1 What is an Operating System? . A program that acts as an intermediary between a user of a computer and the computer hardware . Operating system goals: o Execute user programs and make solving user problems easier. o Make the computer system convenient to use . Use the computer hardware in an efficient manner CSE480/CIS700 S. Fischmeister 2 1 Computer System Components 1. Hardware – provides basic computing resources (CPU, memory, I/O devices) 2. Operating system – controls and coordinates the use of the hardware among the various application programs for the various users 3. Applications programs – define the ways in which the system resources are used to solve the computing problems of the users (compilers, database systems, video games, business programs) 4. Users (people, machines, other computers) CSE480/CIS700 S. Fischmeister 3 Abstract View of System Components CSE480/CIS700 S. Fischmeister 4 2 What is an RTOS? . Often used as a control device in a dedicated application such as controlling scientific experiments, medical imaging systems, industrial control systems, and some display systems . Well-defined fixed-time constraints CSE480/CIS700 S. Fischmeister 5 More Precisely? . The system allows access to sensitive resources with defined response times. o Maximum response times are good for hard real-time o Average response times are ok for soft real-time . Any system that provides the above can be classified as a real-time system o 10us for a context switch, ok? o 10s for a context switch, ok? CSE480/CIS700 S. Fischmeister 6 3 Taxonomy of RTOSs . -
A Hardware Preemptive Multitasking Mechanism Based on Scan-Path Register Structure for FPGA-Based Reconfigurable Systems
A Hardware Preemptive Multitasking Mechanism Based on Scan-path Register Structure for FPGA-based Reconfigurable Systems S. Jovanovic, C. Tanougast and S. Weber Université Henri Poincaré, LIEN, 54506 Vandoeuvre lès Nancy, France [email protected] Abstract all the registers as well as all memories used in the circuit In this paper, we propose a hardware preemptive and to determine the starting point of the restoration multitasking mechanism which uses scan-path register process. On the other hand, the goal of the restoration is to structure and allows identifying the total task’s register restore the task’s context of processing as it was before its size for the FPGA-based reconfigurable systems. The interruption, in order to continue the execution previously main objective of this preemptive mechanism is to stopped. Several techniques allowing the hardware suspend hardware task having low priority, replace it by preemption are proposed in the literature. The pros and high-priority task and restart them at another time cons of mostly used approaches we will disscus in the (and/or from another area of the FPGA in FPGA-based following. designs). The main advantages of the proposed method The readback approach for context saving and storing are that it provides an attractive way for context saving of an outgoing task is one of the approaches which was and restoring of a hardware task without freezing other mostly used for the FPGA-based designs. No additional tasks during pre-emption phases and a small area hardware structures, simple implementation, no extra overhead. We show its feasibility by allowing us to design design efforts and no extra hardware consumption are the a simple computing example as well as the one of the most important advantages of this approach. -
CS 450: Operating Systems Michael Lee <[email protected]>
The Process CS 450: Operating Systems Michael Lee <[email protected]> Agenda - The Process: what is it and what’s in it? - Forms of Multitasking - Tracking processes in the OS - Context switches and Scheduling - Process API a process is a program in execution - its behavior is largely defined by the program being executed - but a process is much more than just a program! Multitasking - Modern general-purpose OSes typically run dozens to hundreds of processes simultaneously - May collectively exceed capacity of hardware - Recall: virtualization allows each process to ignore physical hardware limitations and let OS take care of details CPU/Memory Virtualization - Time-slicing of CPU(s) is performed to simulate concurrency - Memory is partitioned and shared amongst processes - But per-process view is of a uniform address space - Lazy/On-demand loading of processes lowers total burden vs. “Batch” processing - Without multitasking, each program is run from start to finish without interruption from other processes - Including any I/O operations (which may be lengthy!) - Ensures minimal overhead (but at what cost?) - Is virtualization still necessary? Pros/Cons of Multitasking - Pro: may improve resource utilization if we can run some processes while others are blocking - Pro: makes process interaction possible - Con: virtualization introduces overhead (examples?) - Con: possibly reduced overall throughput Forms of Multitasking - Cooperative multitasking: processes voluntarily cede control - Preemptive multitasking: OS polices transitions (how?) - Real-time systems: hard, fixed time constraints (late is wrong!) What’s in a process? - Program (“text”) and data - Static/Stack/Heap memory contents - Registers (e.g., PC, SP, FP) - Open files and devices (e.g., network) - What else? Data vs. -
Scheduling Techniques for Reducing Processor Energy Use in Macos
Scheduling Techniques for Reducing Processor Energy Use in MacOS Jacob R. Lorch and Alan Jay Smith Computer Science Division, EECS Department, UC Berkeley Berkeley, CA 94720-1776 Abstract a number of engineering users. We found that, depending on the machine and user, up to 18±34% of total power was at- The CPU is one of the major power consumers in a tributable to components whose power consumption could be portable computer, and considerable power can be saved by reduced by power management of the processor, i.e. the CPU turning off the CPU when it is not doing useful work. In Ap- and logic that could be turned off when the CPU was inactive. ple's MacOS, however, idle time is often converted to busy This high percentage, combined with our intuition that soft- waiting, and generally it is very hard to tell when no use- ware power management could be signi®cantly improved for ful computation is occurring. In this paper, we suggest sev- the processor, led us to conclude that the most important tar- eral heuristic techniques for identifying this condition, and get for further research in software power management was for temporarily putting the CPU in a low-power state. These the processor. techniques include turning off the processor when all pro- Many modern microprocessors have low-power states, in cesses are blocked, turning off the processor when processes which they consume little or no power. To take advantage of appear to be busy waiting, and extending real time process such low-power states, the operating system needs to direct sleep periods. -
Types of Operating System 3
Types of Operating System 3. Batch Processing System The OS in the early computers was fairly simple. Its major task was to transfer control automatically from one job to the next. The OS was always resident in memory. To speed up processing, operators batched together jobs with similar requirement/needs and ran them through the computer as a group. Thus, the programmers would leave their programs with the operator. The operator would sort programs into batches with similar requirements and, as the computer became available, would run each batch. The output from each job would be sent back to the appropriate programmer. Memory layout of Batch System Operating System User Program Area Batch Processing Operating System JOBS Batch JOBS JOBS JOBS JOBS Monitor OPERATING SYSTEM HARDWARE Advantages: ➢ Batch processing system is particularly useful for operations that require the computer or a peripheral device for an extended period of time with very little user interaction. ➢ Increased performance as it was possible for job to start as soon as previous job is finished without any manual intervention. ➢ Priorities can be set for different batches. Disadvantages: ➢ No interaction is possible with the user while the program is being executed. ➢ In this execution environment , the CPU is often idle, because the speeds of the mechanical I/O devices are intrinsically slower than are those of electronic devices. 4. Multiprogramming System The most important aspect of job scheduling is the ability to multi-program. Multiprogramming increases CPU utilization by organizing jobs so that CPU always has one to execute. The idea is as follows: The operating system keeps several jobs in memory simultaneously. -
I.T.S.O. Powerpc an Inside View
SG24-4299-00 PowerPC An Inside View IBM SG24-4299-00 PowerPC An Inside View Take Note! Before using this information and the product it supports, be sure to read the general information under “Special Notices” on page xiii. First Edition (September 1995) This edition applies to the IBM PC PowerPC hardware and software products currently announced at the date of publication. Order publications through your IBM representative or the IBM branch office serving your locality. Publications are not stocked at the address given below. An ITSO Technical Bulletin Evaluation Form for reader′s feedback appears facing Chapter 1. If the form has been removed, comments may be addressed to: IBM Corporation, International Technical Support Organization Dept. JLPC Building 014 Internal Zip 5220 1000 NW 51st Street Boca Raton, Florida 33431-1328 When you send information to IBM, you grant IBM a non-exclusive right to use or distribute the information in any way it believes appropriate without incurring any obligation to you. Copyright International Business Machines Corporation 1995. All rights reserved. Note to U.S. Government Users — Documentation related to restricted rights — Use, duplication or disclosure is subject to restrictions set forth in GSA ADP Schedule Contract with IBM Corp. Abstract This document provides technical details on the PowerPC technology. It focuses on the features and advantages of the PowerPC Architecture and includes an historical overview of the development of the reduced instruction set computer (RISC) technology. It also describes in detail the IBM Power Series product family based on PowerPC technology, including IBM Personal Computer Power Series 830 and 850 and IBM ThinkPad Power Series 820 and 850. -
Preemptive Multitasking on Atmel® AVR® Microcontroller
Advances in Information Science and Computer Engineering Preemptive Multitasking on Atmel® AVR® Microcontroller HABIBUR RAHMAN, Senthil Arumugam Muthukumaraswamy School of Engineering & Physical Sciences Heriot Watt University Dubai Campus Dubai International Academic City UNITED ARAB EMIRATES [email protected]; [email protected] Abstract: - This paper demonstrates the need for multitasking and scenario where multitasking is the only solution and how it can be achieved on an 8-bit AVR® microcontroller. This project explains how to create a simple kernel in a single C file, and execute any number of tasks in a multithreaded fashion. It first explains how the AVR® engine works and how it switches between different tasks using preemptive scheduling algorithm with the flexibility of blocking a task to allowing it more execution time based on their priority level. The code written for this project is basically in C, however the kernel code is mostly assembly functions called by C. The development environment is Atmel Studio®. The code is in such a way that it can be ported over any 8-bit AVR® microcontroller, however, this project demonstrates the results in both simulation and hardware chip on device Atmega8A. Key-Words: - AVR®, Microcontroller, Threading, Preemptive Scheduling, Multitasking. 1 Introduction architecture and will eventually lead to downloading Microcontroller development has been and compiling hundreds of files according to the exponential over the past two decades. Development provided operating system instructions and also in terms of speed, transistor density, multi-core spend time learning how to use it. embedding as well as number of peripheral subsystem on SoC(System on Chip) is common, and But if the user who has basic understanding of C development tools and compilers have been created language and very good understanding on that allows writing code for microcontroller on microcontroller wants to implement multitasking for higher level of abstraction layer an easy task.