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Operating System Organization

3. Operating System Organization. Purpose of an OS. Coordinate Use of the Abstractions. Processes. The Abstractions. Create the Abstractions. OS Requirements. Provide resource abstractions Process abstraction of CPU/memory use Address space

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Operating System Organization

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  1. Operating Systems: A Modern Perspective, Chapter 3

  2. 3 Operating SystemOrganization Operating Systems: A Modern Perspective, Chapter 3

  3. Purpose of an OS Coordinate Use of the Abstractions Processes The Abstractions Create the Abstractions Operating Systems: A Modern Perspective, Chapter 3

  4. OS Requirements • Provide resource abstractions • Process abstraction of CPU/memory use • Address space • Thread abstraction of CPU within address space • Resource abstraction • “Anything a process can request that can block the process if it is unavailable” • NT uses “object abstraction” to reference resources • File abstraction of secondary storage use Operating Systems: A Modern Perspective, Chapter 3

  5. DOS -- Resource Abstraction Only Program Program Libraries Program OS Services ROM Routines Processor(s) Main Memory Devices Operating Systems: A Modern Perspective, Chapter 3

  6. OS Requirements (cont) • Provide resource abstractions • Manage resource sharing • Time/space-multiplexing • Exclusive use of a resource • Isolation • Managed sharing Operating Systems: A Modern Perspective, Chapter 3

  7. Process Process Process Program Program Program State State State Abstraction & Sharing Libraries • OS Services • Abstraction • Manage sharing ROM Routines Processor(s) Main Memory Devices Operating Systems: A Modern Perspective, Chapter 3

  8. OS Design Constraints • Performance • Protection and security • Correctness • Maintainability • Commercial factors • Standards and open systems Operating Systems: A Modern Perspective, Chapter 3

  9. Performance • The OS is an overhead function should not use too much of machine’s resources • Minimum functionality is to implement abstractions • Additional function must be traded off against performance • DOS: one process • UNIX: low level file system Operating Systems: A Modern Perspective, Chapter 3

  10. Protection & Security • Multiprogramming  resource sharing • Therefore, need software-controlled resource isolation • Security policy: Sharing strategy chosen by computer’s owner • Protection mechanism: Tool to implement a family of security policies Operating Systems: A Modern Perspective, Chapter 3

  11. Correctness & Maintainability • Security depends on correct operation of software trusted vs untrusted software • Maintainability relates to ability of software to be changed • If either is sufficiently important, can limit the function of the OS • Guiding a manned spaceship • Managing a nuclear reactor Operating Systems: A Modern Perspective, Chapter 3

  12. Device Management Device-Independent Part Device-Dependent Part Device-Dependent Part Device-Dependent Part … Device Device Device Operating Systems: A Modern Perspective, Chapter 3

  13. Process, Thread, and Resource Management Thread Abstraction Process Abstraction Generic Resource Manager Multiprogramming Other … Primary Memory Abstract Resources Processor Operating Systems: A Modern Perspective, Chapter 3

  14. Memory Management Isolation & Sharing Virtual Memory Block Allocation Process Manager Primary Memory Storage Devices Operating Systems: A Modern Perspective, Chapter 3

  15. Exclusive Access to a Resource Processor Process A Process B A’s Protected Object Supervisor Program Operating Systems: A Modern Perspective, Chapter 3

  16. Processor Modes • Mode bit: Supervisor or User mode • Supervisor mode • Can execute all machine instructions • Can reference all memory locations • User mode • Can only execute a subset of instructions • Can only reference a subset of memory locations Operating Systems: A Modern Perspective, Chapter 3

  17. Kernels • The part of the OS critical to correct operation (trusted software) • Executes in supervisor mode • The trap instruction is used to switch from user to supervisor mode, entering the OS Operating Systems: A Modern Perspective, Chapter 3

  18. Supervisor and User Memory User Space User Process Supervisor Process Supervisor Space Operating Systems: A Modern Perspective, Chapter 3

  19. send(…, A, …); receive(…, B, …); send/receive receive(…A, …); … send(…, B, …); Procedure Call and Message Passing Operating Systems call(…); trap return; Operating Systems: A Modern Perspective, Chapter 3

  20. System Call Using the trap Instruction … fork(); … Trap Table Kernel fork() { … trap N_SYS_FORK() … } sys_fork() sys_fork() { /* system function */ … return; } Operating Systems: A Modern Perspective, Chapter 3

  21. A Thread Performing a System Call User Space Kernel Space Thread fork(); sys_fork() { } Operating Systems: A Modern Perspective, Chapter 3

  22. File Manager Memory Manager Device Manager Basic Operating System Organization Process, Thread & Resource Manager Processor(s) Main Memory Devices Operating Systems: A Modern Perspective, Chapter 3

  23. The UNIX Architecture Interactive User Libraries Commands Application Programs … OS System Call Interface Trap Table Device Driver • Monolithic Kernel Module • Process Management • Memory Management • File Management • Device Mgmt Infrastructure Device Driver … Driver Interface Device Driver Operating Systems: A Modern Perspective, Chapter 3

  24. Microkernel Organization Process Process Libraries Process User Supervisor Server Server Server Device Drivers Microkernel Processor(s) Main Memory Devices Operating Systems: A Modern Perspective, Chapter 3

  25. Windows NT Organization Process Process T T Process T T T T Libraries T T T Process Management Memory Management File Management Device Mgmt Infrastructure Subsystem Subsystem Subsystem User Supervisor I/O Subsystem NT Executive NT Kernel Hardware Abstraction Layer Processor(s) Main Memory Devices Operating Systems: A Modern Perspective, Chapter 3

  26. Monitoring the Kernel Process Process T Task Manager T Process T T T T Libraries T T T pview pstat Subsystem Subsystem Subsystem User Supervisor I/O Subsystem NT Executive NT Kernel Hardware Abstraction Layer Processor(s) Main Memory Devices Operating Systems: A Modern Perspective, Chapter 3

  27. Operating Systems: A Modern Perspective, Chapter 4

  28. 4 ComputerOrganization Operating Systems: A Modern Perspective, Chapter 4

  29. Stored Program Computers and Electronic Devices Pattern Jacquard Loom Variable Program Stored Program Device Fixed Electronic Device Operating Systems: A Modern Perspective, Chapter 4

  30. Assembly Language ; Code for a = b + c load R3,b load R4,c add R3,R4 store R3,a ; Code for d = a - 100 load R4,=100 subtract R3,R4 store R3,d Program Specification Source int a, b, c, d; . . . a = b + c; d = a - 100; Operating Systems: A Modern Perspective, Chapter 4

  31. Machine Language 10111001001100…1 10111001010000…0 10100111001100…0 10111010001100…1 10111001010000…0 10100110001100…0 10111001101100…1 Machine Language Assembly Language ; Code for a = b + c load R3,b load R4,c add R3,R4 store R3,a ; Code for d = a - 100 load R4,=100 subtract R3,R4 store R3,d Operating Systems: A Modern Perspective, Chapter 4

  32. The von Neumann Architecture Central Processing Unit (CPU) Arithmetical Logical Unit (ALU) Control Unit (CU) Address Bus Data Bus Device Primary Memory Unit (Executable Memory) Operating Systems: A Modern Perspective, Chapter 4

  33. The ALU load R3,b load R4,c add R3,R4 store R3,a Right Operand Left Operand R1 R2 . . . Rn Functional Unit Status Registers Result To/from Primary Memory Operating Systems: A Modern Perspective, Chapter 4

  34. load R3,b load R4,c add R3,R4 store R3,a Fetch Unit 10111001001100…1 10111001010000…0 10100111001100…0 10111010001100…1 3050 PC Decode Unit IR load R4, c Execute Unit Control Unit Control Unit 3046 3050 3054 3058 Primary Memory Operating Systems: A Modern Perspective, Chapter 4

  35. Control Unit Operation • Fetch phase: Instruction retrieved from memory • Execute phase: ALU op, memory data reference, I/O, etc. PC = <machine start address>; IR = memory[PC]; haltFlag = CLEAR; while(haltFlag not SET) { execute(IR); PC = PC + sizeof(INSTRUCT); IR = memory[PC]; // fetch phase }; Operating Systems: A Modern Perspective, Chapter 4

  36. 1234 98765 read 1. Load MAR with address 2. Load Command with “read” 3. Data will then appear in the MDR Primary Memory Unit 0 MAR 1 2 MDR Command 1234 98765 Read Op: n-1 Operating Systems: A Modern Perspective, Chapter 4

  37. Device manager • Program to manage device controller • Supervisor mode software Abstract I/O Machine The Device-Controller-Software Relationship Application Program Software in the CPU Device Controller Device Operating Systems: A Modern Perspective, Chapter 4

  38. busy done 0 0 idle 0 1 finished 1 0 working 1 1 (undefined) Device Controller Interface . . . busy done Error code . . . Command Status Data 0 Data 1 Logic Data n-1 Operating Systems: A Modern Perspective, Chapter 4

  39. Performing a Write Operation while(deviceNo.busy || deviceNo.done) <waiting>; deviceNo.data[0] = <value to write> deviceNo.command = WRITE; while(deviceNo.busy) <waiting>; deviceNo.done = TRUE; • Devices much slower than CPU • CPU waits while device operates • Would like to multiplex CPU to a different process while I/O is in process Operating Systems: A Modern Perspective, Chapter 4

  40. … … … Ready Processes Ready Processes Ready Processes CPU CPU Device Device I/O Operation Uses CPU CPU-I/O Overlap CPU Device Operating Systems: A Modern Perspective, Chapter 4

  41. Determining When I/O is Complete CPU Interrupt Pending Device Device Device • CPU incorporates an “interrupt pending” flag • When device.busy  FALSE, interrupt pending flag is set • Hardware “tells” OS that the interrupt occurred • Interrupt handler part of the OS makes process ready to run Operating Systems: A Modern Perspective, Chapter 4

  42. memory[1] contains the address of the interrupt handler Control Unit with Interrupt (Hardware) PC = <machine start address>; IR = memory[PC]; haltFlag = CLEAR; while(haltFlag not SET) { execute(IR); PC = PC + sizeof(INSTRUCT); IR = memory[PC]; if(InterruptRequest) { memory[0] = PC; PC = memory[1] }; Operating Systems: A Modern Perspective, Chapter 4

  43. Interrupt Handler (Software) interruptHandler() { saveProcessorState(); for(i=0; i<NumberOfDevices; i++) if(device[i].done) goto deviceHandler(i); /* something wrong if we get to here … */ deviceHandler(int i) { finishOperation(); returnToScheduler(); } Operating Systems: A Modern Perspective, Chapter 4

  44. A Race Condition saveProcessorState() { for(i=0; i<NumberOfRegisters; i++) memory[K+i] = R[i]; for(i=0; i<NumberOfStatusRegisters; i++) memory[K+NumberOfRegisters+i] = StatusRegister[i]; } PC = <machine start address>; IR = memory[PC]; haltFlag = CLEAR; while(haltFlag not SET) { execute(IR); PC = PC + sizeof(INSTRUCT); IR = memory[PC]; if(InterruptRequest && InterruptEnabled) { disableInterupts(); memory[0] = PC; PC = memory[1] }; Operating Systems: A Modern Perspective, Chapter 4

  45. Revisiting the trap Instruction (Hardware) executeTrap(argument) { setMode(supervisor); switch(argument) { case 1: PC = memory[1001]; // Trap handler 1 case 2: PC = memory[1002]; // Trap handler 2 . . . case n: PC = memory[1000+n];// Trap handler n }; • The trap instruction dispatches a trap handler routine atomically • Trap handler performs desired processing • “A trap is a software interrupt” Operating Systems: A Modern Perspective, Chapter 4

  46. Direct Memory Access Primary Memory Primary Memory CPU CPU Controller Controller Device Device Operating Systems: A Modern Perspective, Chapter 4

  47. Addressing Devices Primary Memory Primary Memory Memory Addresses Device 0 Device 0 Memory Addresses Device 1 Device 1 Device Addresses Device n-1 Device n-1 Operating Systems: A Modern Perspective, Chapter 4

  48. Polling I/O … // Start the device … While((busy == 1) || (done == 1)) wait(); // Device I/O complete … done = 0; Software busy done … while((busy == 0) && (done == 1)) wait(); // Do the I/O operation busy = 1; … Hardware Operating Systems: A Modern Perspective, Chapter 4

  49. Fetch-Execute Cycle with an Interrupt while (haltFlag not set during execution) { IR = memory[PC]; PC = PC + 1; execute(IR); if (InterruptRequest) { /* Interrupt the current process */ /* Save the current PC in address 0 */ memory[0] = PC; /* Branch indirect through address 1 */ PC = memory[1]; } } Operating Systems: A Modern Perspective, Chapter 4

  50. Detecting an Interrupt CPU InterruptRequest flag Device Device Device Operating Systems: A Modern Perspective, Chapter 4

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