NWI-IBC019: Operating systems. Nils Jansen and Bernard van Gastel

Transcription

1 NWI-IBC019: Operating systems Nils Jansen and Bernard van Gastel

2 Introduction - lecturer - Nils Jansen Aachen, Germany Austin, Texas Research: Formal Verification, Machine Learning, Robotics Hobbies: Reading, Eating, Bars, Trumpet, Guitar

3 Introduction - lecturer - Bernard van Gastel Studied in Nijmegen (active in o.a. Thalia, Olympus and Dance Fever) Research energy efficiency of software correctness of systems (both hardware/software; Intel project) Before going back to Computer Science, I had my own app company, and was a scientific programmer in the hospital (radiology). I like: efficiency / multithreading / scalability / C++ (templates!) snowboarding and skiing making apps (best if combined with craft beer)

4 Introduction - contents Foundation of computer science Still very relevant in modern times, with lots of developments: containers, VMs, SaaS, unikernels, Focus on relevant principles and concepts for operating systems: concurrency (processes & threads) en synchronisation correctness memory management and virtual memory resource allocation and scheduling These principles and concepts are applicable to more subject in Computer Science (and outside thereof)

5 Introduction - practical Website on OpenCourseWare: Enrol in OSIRIS/Blackboard. Book: Operating System Concepts, 9th edition Exam on is `open book. Final grade: exam (50%) en two assignments (each 25%) By participating actively in the lab sessions, you can earn a bonus point for your exam. (definition participating actively: at least 6 van de 8 weekly assignments are graded satisfactory ). Fine print: Max grade for exam including bonus is 10,0. You need at least a 5.0 excluding bonus on the exam to pass the course.

6 Introduction - meetings and assignments Every week lecture (Monday 15:45-17:30) we will focus on insight, not necessary talking about all the mandatory subjects! Every week practicals ( werkcollege ; sign up for it today) individual (!) weekly assignments can be found on OpenCourseWare website hand in before Sunday 23:59 during the next session the main points will be discussed shortly Two larger assignments individual (!) one about creating a shell; one about synchronisation/concurrency first one should be handed in before Sunday October 1, 23:59

7 Introduction - time investment 3 ECTS Lectures: Reading: Practicals: Assignments: Exam: Total: 16 hours 16 hours 20 hours 30 hours 2 hours 84 hours

8 Introduction chapter 1

9 Long ago (or currently when using microcontrollers) No memory organisation (or isolation) No processes No protection of the memory No differentiation between code and data About 70 years ago: larger mainframes with more tasks Administration of these tasks was necessary First operating system had a simple goal: batchprocessing

10 who is who?

11 who is who? Brian Kernighan Linus Torvalds Andrew Tanenbaum Dennis Ritchie, Ken Thompson en PDP11 Dennis Ritchie Edsger Dijkstra Ken Thompson Tony Hoare

12 OS development evolved to include these tasks offer a common interface of hardware to applications (with a hardware abstraction layer). regulate / manage the interaction with hardware (e.g. batch processing). manage the execution of (multiple) active applications, called processes. facilitate the communication (and synchronisation) between processes among themselves, and between the OS and processes. management of memories (both permanent and transient; e.g. solid state and RAM).

13 Conditions to operating systems Reliability (e.g. crashes). Performance. Security. Energy efficiency. Without these conditions, an operating system would not be so useful as they are today. It is essential that we focus on these properties.

14 Recent development: energy efficiency Often contra-productive for other requirements, such as: latency scalability throughput reliability performance Last couple of years energy became more important. All parts of a modern OS are adjusted for this: limits on allowable behaviour (see Android Oreo changes), how hardware is accessed, when timers of applications are fired,

15 Reliability in operating systems User mode restrictions on access to resources and memory, only a subset of hardware instructions are allowed. Kernel mode (or supervisor/system/control mode) full access to resources and memory, all hardware instructions are allowed. Hardware support for this is included in modern hardware. When the system is invoked, a special instruction is executed. Because of these modes: if a program crashes, the system does not crash (this was not the case in the past or on microcontrollers!) Definition: kernel is the part of the operating system that runs with elevated permissions (in kernel mode).

16 An operating system consists of a program, called the kernel, that manages the execution of applications and connects applications with the hardware. Components of the kernel: scheduler (switch between processes), memory management (translation of memory addresses, keeping track of usage), file system (how files and directories are stored on disk), drivers (software that know how to manage hardware components),.

17 List of operating systems RISC OS MS-DOS OS/2 AIX macos Windows 7 FreeBSD ios OpenBSD Darwin NetBSD Unix System V CP/M VMS ChromeOS Android Multics HP-UX OS/360 Tizen PikeOS QNX Solaris MINIX L4 OSv

18 Summary OS tasks were slowly included over time: abstraction of hardware manage hardware multitasking communication between processes and OS management (of e.g. memory) Important conditions reliability efficiency security ease of use (both for programmer and user) Modern OS have a central component with elevated permissions, called the kernel, which consists of: scheduler, memory management, file system and drivers,.

19 System structures chapter 2

20 System calls Interface to the system for applications. Is used for: process control file manipulation device management information maintenance communication

21 System calls - structure #include <unistd.h> ssize_t read(int fd, void *buf, size_t count) return value function name parameters

22 How system calls are handled user application open ( ) user mode kernel mode system call interface i open ( ) Implementation of open ( ) system call return Figure 2.6 The handling of a user application invoking the open() system call.

23 System call implementation Typically, a number associated with each system call. System-call interface maintains a table indexed according to these numbers. The system call interface invokes the intended system call in OS kernel and returns status of the system call and any return values. The caller need know nothing about how the system call is implemented. Just needs to obey API and understand what OS will do as a result call. Most details of OS interface hidden from programmer by API (managed by run-time support library; set of functions built into libraries included with compiler).

24 System boot When power initialised on system, execution starts at a fixed memory location. Firmware ROM used to hold initial boot code. Operating system must be made available to hardware so hardware can start it. Small piece of code bootstrap loader, stored in ROM locates the kernel, loads it into memory, and starts it. Kernel loads and system is then running.

25 Process concept chapter 3

26 Definition process Process is an application being executed. A process is a task that can be assigned and executed on a specific processor. A unit of activity, with the following properties: a chunk of (hardware) instructions current program state assigned system resources Without a processor no process! Process application!

27 Process is central to operating system For all multiprogramming operating systems, the concept process is essential. Everything is a process: shell interface browser Important condition: processes are independent of each other, i.e., they are isolated. They cannot influence each other directly (without the consent of the other process). Consequence: every proces has their own isolated piece of memory.

28 Concept: concurrency With parallelism multiple processes are executed at the same time, e.g. multi-core or a cluster of servers. Interleaved execution is the fast switching of multiple processes on only one execution unit. Concurrency is apparent execution of multiple processes at the same time. Concurrency is always present inside one computer: hardware components execute parallel to the processor and each other, processes are executed interleaved or in parallel. Concurrency is present outside of the one computer: a network of computers is parallel. Problem: messages can arrive later as intended. Problem: mutual exclusion.

29 Execution of processes Processes were the first form of concurrency (on a high level). For both, switching between processes is needed. For both, administration of contexts of processes is needed. For both, isolation of processes is needed. A multitasking operating system creates the illusion of multiple execution units (processors/cores) with multiple independent memories.

30 Administration of processes Overview of all processes that currently exist in the operating system. Context of processes include: process state program counter CPU registers CPU-scheduling information memory management information accounting information I/O status information. This context is stored in a process control block (PCB). This PCB contains all the information to pause and restart a process, without the process itself noticing it directly.

31 States of processes new the processes is being created. ready the process is waiting to be assigned to a processor. running instructions are being executed. waiting the process is waiting for some event to occur. terminated the process has finished execution.

32 States of processes new admitted ready event completion interrupt dispatch waiting running event-wait exit terminated

33 States of processes new ready admitted suspend activate suspended ready interrupt dispatch running exit event completion event-wait waiting event completion suspend suspended waiting activate terminated

34 States of processes new ready admitted event completion suspend activate suspended ready interrupt dispatch running exit terminated event-wait waiting waiting waiting waiting waiting event completion suspend activate suspended suspended waiting suspended waiting suspended waiting suspended waiting waiting

35 Context switches Switching the running process on a processor/core implies switching the process context (PCB). Cost a lot of time! (performance ) Has to store the whole context of the old process, and restore the whole context of the new process. Will probably also be bad for caching in your CPU.

36 Process creation and communication There are special system calls for process creation. On UNIX systems foremost there is fork(). Likewise for communication between processes, mainly pipe() (for starters). Both needed to be managed by the operating system because of the isolation property. You will experience this with the first assignment about creating your own shell.

37 Summary Process is a central concept. Processes have a state, with modern operating systems the number of states can be high. Scheduler kiest welk proces uitgevoerd wordt Proces context wordt van elk proces bijgehouden Preemptive multitasking User mode vs kernel mode

38 Upcoming Next week in lecture: threads (splitting the process concept). Tutorials: introduction to the shell assignment. Read the book: chapter 1 up to and including 1.9 chapter 2 up to and including chapter 3 up to and including