Resource Management

1
Resource Management

• Davis Rajkumar (6th), Chp. 6

2
Overview

• Measures of computer performance
• Memory management
• Resident and transient routines
• Processor management
• Virtual machine
• Deadlock

3
Operating System Functions

• Manage resources
• User interface people and programs
• File system programs and data stored in
  secondary storage
• Device management IOCS, peripheral devices
• Memory management memory space
• Processor management processor time
• Communication services network resources

4
Measure of Computer Performance

• Throughput Total execution time / Total elapse
  time
• Turnaround Job finish time job start time
• Response time Time receive attention request
  time
• Availability Time required to get on system
  sometimes up time
• Security How safe is the system?
• Reliability Probability system will perform as
  expected
• Robustness Ability to recover from errors or
  unusual conditions fault tolerance
• Cost Total cost includes acquisition, updates,
  and operation
• Ease of use Training time for administrators,
  operators, and users

5
Memory Management

• Managing available pool of memory
• Allocating space to application routines
• Making sure they do not interfere with each other
• Hidden from users of operating system

6
Resident and Transient Routines

• Operating system collection of routines
• Resident routines
• Loaded in memory for immediate use, such as
  kernel and routines used by device interrupts
• Windows 3-finger salute Solaris ps -ef
• Transient routines stored in secondary storage
  until needed

7
Memory and Concurrency

• Multiple programs using the same system resources
  over given period of time is called concurrency
• Concurrent over given period of time
• Simultaneous at same instant in time
• Memory must accommodate concurrently
• System control information
• Resident operating system routines
• Transient routines and programs

8
Partitions and Regions

• Fixed-partitions
• Simplest solution to concurrent memory demands
• Divides available memory into fixed-length
  partitions each holds one program
• Partitions established at startup (DOS)
• Regions
• Dynamic memory management
• Portion of memory for resident operating system
  routines
• Portion of memory used for transient routines
• Pool of unstructured space
• Allotted in regions just large enough to met
  routines needs
• Fragmentation
• Little chunks of unused memory spread throughout
  memory space
• Fixed-partition and dynamic memory management
  assume program must have contiguous memory space,
  which causes fragmentation

9
Segmentation and Paging

• Segmentation
• Divides program into independently addressed
  units called segments
• Segments stored in noncontiguous memory
• Requires segment table
• Created when program loaded
• Used to translate relative addresses to absolute
  addresses
• Segments can vary in length
• Paging
• Divides program into fixed-length units called
  pages
• Loaded in contiguous memory
• Addresses have two parts Page number and
  displacement
• Uses Page Table to translate relative address to
  absolute address
• Both
• Combines segmentation and paging
• Address segment, page, displacement

10
Virtual Memory Terms

• Addressing
• Machine instructions use relative addresses
• Base address is starting address in virtual
  memory
• Space allocated on external paging device
• When page put in real memory, pages real
  address put in page table
• Page fault virtual address points to location
  not in real memory
• Thrashing
• Memory full of pages
• Demand for new page requires page swapped out
• System becomes occupied with swapping pages in
  and out
• Memory mapping
• Store image of target file on paging device
• Data transferred using paging mechanism rather
  than physical I/O

11
Virtual Memory

• Processor executes one instruction at time
• Only next instruction needs to be in memory
• Virtual memory loads only currently active page
• Overlays
• Program broken into modules
• Memory area used by transient modules overlaid
  with each module as needed
• Internal to program
• Virtual memory
• External to program
• Loads pages in page pool as needed

12
Process Management

• Allocation of processor time
• Managing processor time
• Hidden from users of operating system

13
Kinds of Execution

• Multiprogramming
• More than one program using processor over period
  of time
• Multiprocessingmore than one processor used by
  one or more programs
• Multitaskingone than one program using available
  processors
• Time-sharing
• Each process gets a slice of the processors
  time

14
Process States
15
Dispatcher

• Process management routine
• Decides which of the ready processes get to use
  the processor

16
Control Blocks

• One per partition
• Holds
• Partition key control flags
• Constants
• Variables
• Form link list each control block points to
  next control block

17
Interrupts

• Electronic signal requesting processors
  attention
• Hardware senses signal, stores current processs
  states putting process in wait state, and starts
  interrupt handlerinterrupt ends
• System processes interrupt and returns processor
  to process in ready state

18
Process Dispatching
19
Queuing and Scheduling Routines

• Processor management concerned with internal
  priorities of program in memory
• Putting program in memory uses two routines
• Queuing manages programs upon entry into process
  queue until space is available
• Scheduler once space is available, selects
  programs from queue to put in memory

20
Virtual Machine

• Allocates abstracted resources to programs
• Each virtual machine has own
• Operating system routines
• Abstracted peripherals
• Memory allocation
• User of virtual machine is operating system

21
Deadlock

• Some resources can only be used by one process at
  a time
• Processor
• Memory location
• I/O device without a queue
• Process must have ALL resources it needs BEFORE
  it can be processed
• If two processes have one of two resources
  needed, other process has other resource, and
  neither will relinquish its current resource
  deadlock occurs
• Dining philosophers problem