The Joy of Scheduling
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Kernel-Scheduled Entities for Freebsd
Kernel-Scheduled Entities for FreeBSD Jason Evans [email protected] November 7, 2000 Abstract FreeBSD has historically had less than ideal support for multi-threaded application programming. At present, there are two threading libraries available. libc r is entirely invisible to the kernel, and multiplexes threads within a single process. The linuxthreads port, which creates a separate process for each thread via rfork(), plus one thread to handle thread synchronization, relies on the kernel scheduler to multiplex ”threads” onto the available processors. Both approaches have scaling problems. libc r does not take advantage of multiple processors and cannot avoid blocking when doing I/O on ”fast” devices. The linuxthreads port requires one process per thread, and thus puts strain on the kernel scheduler, as well as requiring significant kernel resources. In addition, thread switching can only be as fast as the kernel's process switching. This paper summarizes various methods of implementing threads for application programming, then goes on to describe a new threading architecture for FreeBSD, based on what are called kernel- scheduled entities, or scheduler activations. 1 Background FreeBSD has been slow to implement application threading facilities, perhaps because threading is difficult to implement correctly, and the FreeBSD's general reluctance to build substandard solutions to problems. Instead, two technologies originally developed by others have been integrated. libc r is based on Chris Provenzano's userland pthreads implementation, and was significantly re- worked by John Birrell and integrated into the FreeBSD source tree. Since then, numerous other people have improved and expanded libc r's capabilities. At this time, libc r is a high-quality userland implementation of POSIX threads. -
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. -
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 . -
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. -
2. Virtualizing CPU(2)
Operating Systems 2. Virtualizing CPU Pablo Prieto Torralbo DEPARTMENT OF COMPUTER ENGINEERING AND ELECTRONICS This material is published under: Creative Commons BY-NC-SA 4.0 2.1 Virtualizing the CPU -Process What is a process? } A running program. ◦ Program: Static code and static data sitting on the disk. ◦ Process: Dynamic instance of a program. ◦ You can have multiple instances (processes) of the same program (or none). ◦ Users usually run more than one program at a time. Web browser, mail program, music player, a game… } The process is the OS’s abstraction for execution ◦ often called a job, task... ◦ Is the unit of scheduling Program } A program consists of: ◦ Code: machine instructions. ◦ Data: variables stored and manipulated in memory. Initialized variables (global) Dynamically allocated (malloc, new) Stack variables (function arguments, C automatic variables) } What is added to a program to become a process? ◦ DLLs: Libraries not compiled or linked with the program (probably shared with other programs). ◦ OS resources: open files… Program } Preparing a program: Task Editor Source Code Source Code A B Compiler/Assembler Object Code Object Code Other A B Objects Linker Executable Dynamic Program File Libraries Loader Executable Process in Memory Process Creation Process Address space Code Static Data OS res/DLLs Heap CPU Memory Stack Loading: Code OS Reads on disk program Static Data and places it into the address space of the process Program Disk Eagerly/Lazily Process State } Each process has an execution state, which indicates what it is currently doing ps -l, top ◦ Running (R): executing on the CPU Is the process that currently controls the CPU How many processes can be running simultaneously? ◦ Ready/Runnable (R): Ready to run and waiting to be assigned by the OS Could run, but another process has the CPU Same state (TASK_RUNNING) in Linux. -
Processor Affinity Or Bound Multiprocessing?
Processor Affinity or Bound Multiprocessing? Easing the Migration to Embedded Multicore Processing Shiv Nagarajan, Ph.D. QNX Software Systems [email protected] Processor Affinity or Bound Multiprocessing? QNX Software Systems Abstract Thanks to higher computing power and system density at lower clock speeds, multicore processing has gained widespread acceptance in embedded systems. Designing systems that make full use of multicore processors remains a challenge, however, as does migrating systems designed for single-core processors. Bound multiprocessing (BMP) can help with these designs and these migrations. It adds a subtle but critical improvement to symmetric multiprocessing (SMP) processor affinity: it implements runmask inheritance, a feature that allows developers to bind all threads in a process or even a subsystem to a specific processor without code changes. QNX Neutrino RTOS Introduction The QNX® Neutrino® RTOS has been Effective use of multicore processors can multiprocessor capable since 1997, and profoundly improve the performance of embedded is deployed in hundreds of systems and applications ranging from industrial control systems thousands of multicore processors in to multimedia platforms. Designing systems that embedded environments. It supports make effective use of multiprocessors remains a AMP, SMP — and BMP. challenge, however. The problem is not just one of making full use of the new multicore environments to optimize performance. Developers must not only guarantee that the systems they themselves write will run correctly on multicore processors, but they must also ensure that applications written for single-core processors will not fail or cause other applications to fail when they are migrated to a multicore environment. To complicate matters further, these new and legacy applications can contain third-party code, which developers may not be able to change. -
CPU Scheduling
CPU Scheduling CS 416: Operating Systems Design Department of Computer Science Rutgers University http://www.cs.rutgers.edu/~vinodg/teaching/416 What and Why? What is processor scheduling? Why? At first to share an expensive resource ± multiprogramming Now to perform concurrent tasks because processor is so powerful Future looks like past + now Computing utility – large data/processing centers use multiprogramming to maximize resource utilization Systems still powerful enough for each user to run multiple concurrent tasks Rutgers University 2 CS 416: Operating Systems Assumptions Pool of jobs contending for the CPU Jobs are independent and compete for resources (this assumption is not true for all systems/scenarios) Scheduler mediates between jobs to optimize some performance criterion In this lecture, we will talk about processes and threads interchangeably. We will assume a single-threaded CPU. Rutgers University 3 CS 416: Operating Systems Multiprogramming Example Process A 1 sec start idle; input idle; input stop Process B start idle; input idle; input stop Time = 10 seconds Rutgers University 4 CS 416: Operating Systems Multiprogramming Example (cont) Process A Process B start B start idle; input idle; input stop A idle; input idle; input stop B Total Time = 20 seconds Throughput = 2 jobs in 20 seconds = 0.1 jobs/second Avg. Waiting Time = (0+10)/2 = 5 seconds Rutgers University 5 CS 416: Operating Systems Multiprogramming Example (cont) Process A start idle; input idle; input stop A context switch context switch to B to A Process B idle; input idle; input stop B Throughput = 2 jobs in 11 seconds = 0.18 jobs/second Avg. -
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.