RedHawkTM Linux® User’s Guide 0898004-300 April 2003 Copyright 2002 by Concurrent Computer Corporation. All rights reserved. This publication or any part thereof is intended for use with Concurrent products by Concurrent personnel, customers, and end–users. It may not be repro- duced in any form without the written permission of the publisher. The information contained in this document is believed to be correct at the time of publication. It is subject to change without notice. Concurrent makes no warranties, expressed or implied, concerning the information contained in this document. To report an error or comment on a specific portion of the manual, photocopy the page in question and mark the cor- rection or comment on the copy. Mail the copy (and any additional comments) to Concurrent Computer Corporation, 2881 Gateway Drive, Pompano Beach, Florida, 33069. Mark the envelope “Attention: Publications Department.” This publication may not be reproduced for any other reason in any form without written permission of the publisher. Linux is a registered trademark of Linus Torvalds. Red Hat is a registered trademark of Red Hat, Inc. RedHawk, iHawk, NightStar, NightTrace, NightSim, NightProbe and NightView are trademarks of Concurrent Com- puter Corporation. POSIX is a registered trademark of the Institute of Electrical and Electronics Engineers, Inc. The X Window System is a trademark of The Open Group. OSF/Motif is a registered trademark of the Open Software Foundation, Inc. Ethernet is a trademark of the Xerox Corporation. NFS is a trademark of Sun Microsystems, Inc. Other products mentioned in this document are trademarks, registered trademarks, or trade names of the manufacturers or marketers of the product with which the marks or names are associated. Printed in U. S. A. Revision History: Level: Effective With: Original Release -- August 2002 000 RedHawk Linux Release 1.1 Previous Release -- December 2002 200 RedHawk Linux Release 1.2 Current Release -- April 2003 300 RedHawk Linux Release 1.3 Preface Scope of Manual This manual consists of three parts. The information in Part 1 is directed towards real-time users. Part 2 is directed towards system administrators. Part 3 consists of backmatter: appendix and index. An overview of the contents of the manual follows. Structure of Manual This guide consists of the following sections: Part 1 - Real-Time User • Chapter 1, Introduction to RedHawk Linux, provides an introduction to the RedHawk Linux operating system and gives an overview of the real-time features included. • Chapter 2, Real-Time Performance, discusses issues involved with achieving real-time performance including interrupt response, process dispatch latency and deterministic program execution. The shielded CPU model is described. • Chapter 3, Real-Time Interprocess Communication, discusses procedures for using the POSIX and System V message-passing facilities. • Chapter 4, Process Scheduling, provides an overview of process scheduling and describes POSIX® scheduling policies and priorities. • Chapter 5, Interprocess Synchronization, describes the interfaces provided by RedHawk Linux for cooperating processes to synchronize access to shared resources. Included are: POSIX counting semaphores, System V semaphores, rescheduling control tools and condition synchronization tools. • Chapter 6, Programmable Clocks and Timers, provides an overview of some of the RCIM and POSIX timing facilities that are available under RedHawk Linux. • Chapter 7, System Clocks and Timers, describes the per-CPU local timer and the system global timer. • Chapter 8, File Systems and Disk I/O, explains the xfs journaling file system and procedures for performing direct disk I/O on the RedHawk Linux operating system. • Chapter 9, Memory Mapping, describes the methods provided by RedHawk Linux for a process to access the contents of another process’ address space. iii RedHawk Linux User’s Guide Part 2 - Administrator • Chapter 10, Configuring and Building the Kernel, provides information on how to configure and build a RedHawk Linux kernel. • Chapter 11, Linux Kernel Crash Dump (LKCD), provides guidelines for saving, restoring and analyzing the kernel memory image using LKCD. • Chapter 12, Pluggable Authentication Modules (PAM), describes the PAM authentication capabilities of RedHawk Linux. • Chapter 13, Device Drivers and Real Time, describes real-time issues involved with writing device drivers for RedHawk Linux. Part 3 - Common Material • Appendix A contains an example program illustrating the System V message queue facility. • The Index contains an alphabetical reference to key terms and concepts and the pages where they occur in the text. Syntax Notation The following notation is used throughout this manual: italic Books, reference cards, and items that the user must specify appear in italic type. Special terms may also appear in italics. list bold User input appears in list bold type and must be entered exactly as shown. Names of directories, files, commands, options and man page references also appear in list bold type. list Operating system and program output such as prompts and messages and listings of files and programs appear in list type. [ ] Brackets enclose command options and arguments that are optional. You do not type the brackets if you choose to specify such options or arguments Related Publications Title Pub No. RedHawk Linux Release Notes Version x.x 0898003 RedHawk Linux Frequency-Based Scheduler (FBS) User’s Guide 0898005 Real-Time Clock and Interrupt Module (RCIM) User’s Guide 0898007 where x.x = release version iv Chapter 0Contents Preface . iii Chapter 1 Introduction to RedHawk Linux Overview . 1-1 RedHawk Linux Kernels . 1-2 System Updates . 1-2 Real-Time Features in RedHawk Linux . 1-3 Processor Shielding . 1-3 Processor Affinity. 1-3 User-level Preemption Control. 1-3 Fast Block/Wake Services . 1-4 RCIM Driver . 1-4 Frequency-Based Scheduler . 1-4 /proc Modifications . 1-4 Kernel Trace Facility . 1-5 ptrace Extensions . 1-5 Kernel Preemption . 1-5 Real-Time Scheduler . 1-5 Low Latency Patches . 1-6 High Resolution Timing . 1-6 Capabilities Support . 1-6 Kernel Debuggers. 1-6 Kernel Core Dumps/Crash Analysis . 1-7 User-Level Spin Locks . 1-7 usermap and /proc mmap . 1-7 Hyper-threading . 1-7 XFS Journaling File System. 1-7 POSIX Real-Time Extensions . 1-8 User Priority Scheduling . 1-8 Memory Resident Processes . 1-8 Memory Mapping and Data Sharing. 1-8 Process Synchronization . 1-9 Asynchronous Input/Output . 1-9 Synchronized Input/Output . 1-9 Real-Time Signal Behavior. 1-9 Clocks and Timers. 1-10 Message Queues . 1-10 Chapter 2 Real-Time Performance Overview of the Shielded CPU Model . 2-1 Overview of Determinism . 2-2 Process Dispatch Latency . 2-2 Effect of Disabling Interrupts. 2-4 Effect of Interrupts . 2-5 Effect of Disabling Preemption . 2-8 Effect of Open Source Device Drivers. 2-9 v RedHawk Linux User’s Guide How Shielding Improves Real-Time Performance . 2-9 Shielding From Background Processes . 2-9 Shielding From Interrupts. 2-10 Shielding From Local Interrupt . 2-10 Interfaces to CPU Shielding. 2-11 Shield Command. 2-11 Shield Command Examples. 2-13 Exit Status . 2-13 Shield Command Advanced Features . 2-13 /proc Interface to CPU Shielding . 2-13 Assigning Processes to CPUs . 2-14 Multiprocessor Control Using mpadvise. 2-15 Assigning CPU Affinity to init . 2-16 Example of Setting Up a Shielded CPU . 2-17 Procedures for Increasing Determinism. 2-20 Locking Pages in Memory . 2-20 Setting the Program Priority . 2-21 Setting the Priority of Deferred Interrupt Processing . 2-21 Waking Another Process. ..