Fundamental Concepts of Operating Systems

Transcription

1 Fundamental Concepts of Operating Systems Minsoo Ryu Real-Time Computing and Communications Lab. Hanyang University

2 1. OS, What and Why? 2. Dual Mode Operation 3. Reusable SW Platform Topics Covered 2 2

3 What is the OS? App developers (set of APIs and services) Users (GUI and windows, file systems) OS developers (?) Device Manufacturers (device drivers) CPU, I/O hardware vendors (responsible for hardware management) 3 3

4 Huge and Complex Red Hat Linux version 7.1 (released April 2001) contained over 30 million lines About 8,000 man-years of development effort Over $1 billion (in year 2000 U.S. dollars) 45M lines of code Linux has 18M lines of code 4 4

5 Difficult to Build and Own OS interfaces a variety of apps and HW components Applications Media player Browser Highest Form of SW in CS Needs Expert Developers Operating System Hardware CPU Memory Terminal Network Miscellaneous Disk Editor Graphic card 5 5

6 Simply, OS is a Big Library An organized collection of reusable program code Bootstrapping, device drivers, scheduling, GUI POSIX Standard API implementations University Library POSIX Standard

7 Common OS Structure App Application 1 Application 2 Application N System Calls GUI Manager Process & Thread Memory Management Inter-process Management OS File System Sync Primitives CPU Scheduling Network Protocols Device Driver Device Driver Interrupt & Exception Handlers Device Driver Device Driver HW Processors, Memory, Storage, Network, Sensors, Actuators 7 7

8 Execution Flow with OS App Application 1 Application 2 Application N thread_create( ) System Calls receive( ) GUI Manager task_create( ) alloc_mem( ) OS File System Sync Primitives schedule( ) proc_protocol( ) Device Driver Device Driver interrupt( ) HW Processors, Memory, Storage, Network, Sensors, Actuators 8 8

9 Execution Flow without OS Event Handler Structure ISR_#1( ) helper_#1( ) ISR_#2( ) SW wait( ) bootstrap( ) interrupt( ) ISR_#3( ) ISR_#n( ) helper_#2( ) helper_#m( ) power ON interrupt HW Processors, Memory, Storage, Network, Sensors, Actuators 9 9

10 Execution Flow without OS Simple Scheduler Structure task_#1( ) task_#2( ) SW wait( ) interrupt( ) schedule( ) task_#3( ) bootstrap( ) task_#n( ) power ON interrupt HW Processors, Memory, Storage, Network, Sensors, Actuators 10 10

11 OS is more than a library 1. Abstraction 2. Protection 3. Illusion 11 11

12 Abstraction Pick out only key features to reduce complexity Provide a clean, uniform, and standard interface to users hiding hardware complexity POSIX Standard APIs Application S/W Application S/W Operating System S/W Hardware Without OS Hardware With OS 12 12

13 System Call Interface System calls provide the interface between application SW and the operating system 13 13

14 System Calls vs. Library Calls 14 14

15 Protection OS has a dual mode mechanism to protect the system from many types of application faults User mode: application code runs Using only non-privileged instructions and/or registers Kernel mode: kernel code runs Using privileged I/O instructions and/or registers 15 15

16 Processor Modes Processors support different privilege modes Intel architectures have four privilege modes ARM architectures have eight privilege modes Intel Protection Rings ARM Processor Modes 16 16

17 Illusion Make hardware limitations go away As if there are infinite number of processors (time sharing) As if there is extremely large memory (virtual memory) Task A Task B Task C Task D Task A (weight 25.0%) Task B (weight 12.5%) Task C (weight 50.0%) Task D (weight 12.5%) time Time Shared Multitasking Virtual Memory 17 17

18 Dual Mode Operation

19 Execution Mode and Context 19 19

20 Program Execution without OS von Neumann machine works by Fetching instructions from memory pointed by program counter Executing them on registers CPU Memory Registers Arithmetic Logic Unit Control Unit pc 0001 LDR r0, [r1] 0002 MUL r1, r2, r ADD r0, r1, # BIC r0, r1, r x x x x code area data area I/O devices screen disk 20 20

21 Program Execution with OS Memory is divided into two spaces User space Kernel space CPU Registers Arithmetic Logic Unit Control Unit pc Memory 0001 LDR r0, [r1] 0002 SWI 0x x x ADD r0, r1, # BIC r0, r1, r x x code data code data user space kernel space 21 21

22 Mode Switching via System Call System calls are similar to function calls, but differ The implementations are in the kernel space They are executed in the kernel mode CPU Memory Registers Arithmetic Logic Unit Control Unit pc 0001 LDR r0, [r1] 0002 SWI 0x x x ADD r0, r1, # BIC r0, r1, r x x code data code data user space kernel space 22 22

23 Mode Switching via System Call CPU Memory CPU Memory Registers Arithmetic Logic Unit Control Unit pc 0001 LDR r0, [r1] 0002 SWI 0x x x ADD r0, r1, # BIC r0, r1, r x x Registers Arithmetic Logic Unit Control Unit pc 0001 LDR r0, [r1] 0002 SWI 0x x x ADD r0, r1, # BIC r0, r1, r x x <before invocation> <after invocation> 23 23

24 System Calls vs. Function Calls Function Call System Call - Caller and callee are in the same process - User space, user mode - Caller and callee are in different spaces - Kernel space, kernel mode 24 24

25 Common SW Structure 25 25

26 OS is a Reusable SW Platform

27 OS is a Reusable Platform OS provides a reusable SW platform Reduced development cost and better software quality Main components Framework Design reuse Inversion of control Libraries (toolkit) Code reuse Kernel HW abstraction Resource management Applications Framework Libraries Kernel Hardware OS Platform 27 27

28 Android Platform Java APPLICATIONS Home Contacts Phone Browser APPLICATION FRAMEWORK Java Package Manager Activity Manager Telephony Manager Window Manager Resource Manager Content Providers Location Manager View System Notification Manager C++ Surface Manager OpenGL ES LIBRARIES Media Framework FreeType SQLite Webkit ANDROID RUNTIME Core Libraries Dalvik Virtual Machine SGL SSL libc C & assembly Display Driver Camera Driver LINUX KERNEL Flash Memory Driver Keypad Driver WiFi Driver Audio Drivers Binder (IPC) Driver Power Management 28 28

29 OS defines the Architecture OS defines the whole SW architecture Ease of SW design and implementation Task Task App change Task Task Framework Libraries architecture reuse Framework Libraries SW architecture Kernel Kernel Hardware HW change Hardware 29 29

30 OS and the Ecosystem App Developers Cars Lock-in & Churn-in Internet of Things Content Providers Operating System Business enabler creating new value chain CEs Mobile devices Wearable devices 30 30