chapter 7 operating system support - yonsei...

YonseiYonsei UniversityUniversity

Chapter 7Chapter 7

Operating SystemOperating SystemSupportSupport

YonseiYonsei UniversityUniversity7-2

• Operating System Overview• Scheduling• Memory Management• Pentium II and PowerPC Memory Management

Contents Contents


• OS is a program that– Manages the computer’s resources, provides

services for programmers – Schedules the execution of other programs

• Objective– Convenience

• Makes a computer more convenient– Efficiency

• Allows the computer system resources to be used in a efficiency manner

OS Objectives & FunctionsOS Objectives & Functions Operation System OverviewOperation System Overview


• To ease a complex task, a set of systems program is provided

• Some of programs are referred to as utilities• These implement use functions that assist

in program creation, the management of files, the control of I/O devices

• Programmers make use of these facilities in developing an application

• OS provides a programmer with a convenient interface for using the system

OS : User/Computer InterfaceOS : User/Computer Interface Operation System OverviewOperation System Overview


Layers of a Computer SystemLayers of a Computer System Operation System OverviewOperation System Overview


• Program Creation– Assists the programmer in creating programs

• Program execution– Handles program execution for user

• Access to I/O devices• Controlled access to files• System access

– Access to the system as a whole and to specific system resource

• Error detection and response• Accounting

OS ServicesOS Services Operation System OverviewOperation System Overview


• OS functions in the same way ordinary computer software; it is a program executed by the processor

• OS frequently relinquishes control and must depend on the processor to allow it to regain control

OS : Resource ManagerOS : Resource Manager Operation System OverviewOperation System Overview


• The OS is nothing more than a computer program

• The OS directs the processor in the use of the other system resources and in timing of its execution of other programs

• Kernel, nucleus – Contains the most frequently used functions in

operating system and at a given time, other portions of the operating system currently in use

• The OS decides when an I/O device can be used by a program in execution, and controls access to and use of files



• Interactive system– User/programmer interacts directly with the computer,

usually through a keyboard/display terminal, the request the execution of a job or to perform a transaction

• Batch system(opposite of interactive)– User’s program is batched together with programs

from other users and submitted by a computer operator

• Independent dimension specifies whether the system employs multiprogramming or not

• Alternative is a uniprogramming system that work only one program at a time

Types of Operating SystemsTypes of Operating Systems Operation System OverviewOperation System Overview


• Early computer(late 1940 to the mid-1950)– No operating system– The processor were run from a console– The program in processor code were loaded via input

device

• Two main problems– Scheduling– Setup time

Early SystemsEarly Systems Operation System OverviewOperation System Overview


• Early processors were very expensive • It was important to maximize processor

utilization• Monitor : Simple batch operating systems• Batch : Job together sequentially• From the point of view of the monitor, it is the

monitor that controls the sequence of events• Resident monitor• When the job is completed, it returns control

to the monitor, which immediately reads in the next job

Simple Batch SystemsSimple Batch Systems Operation System OverviewOperation System Overview


Memory LayoutMemory Layout Operation System OverviewOperation System Overview


Simple Batch SystemsSimple Batch Systems• At a certain point in time, the processor is

executing instructions from the portion of main memory containing the monitor

• These instructions cause the next job to be read in to another portion of main memory

• Monitor handles the scheduling problem• How about the job setup time?

– The monitor handles this as well

• Job control language(JCL)– Used to provide instructions to the monitor

Operation System OverviewOperation System Overview


Overall Format of JobOverall Format of Job

$JOB$FTN...$LOAD$RUN...$END


InstructionsInstructions

DataData


Simple Batch SystemsSimple Batch Systems• Hardware features• Memory protection

– While the user program is executing, it must not alter the memory area containing the monitor

• Timer– Prevent a single job from monopolizing the system

• Privileged instructions– Executed only by the monitor

• Interrupts– Flexibility in relinquishing control to and regaining

control from user programs



MultiprogrammedMultiprogrammed Batch SystemBatch System• The processor is often idle• The problem is that I/O devices are slow• Suppose that there is room for the operating

system and two user programs• When one job needs to wait for I/O, the

processor can switch to the other job, which likely is not waiting for I/O


System Utilization Example

Percent CPU util = 0.0001/0.0031 = 0.032 = 3.2 %

0.0031 secondsTOTAL

0.0015 secondsWrite one record

0.0001 secondsExecute 100 instructions

0.0015 secondsRead one record


Multiprogramming ExampleMultiprogramming Example Operation System OverviewOperation System Overview

• Uniprogramming



• Multiprogramming with two programs


Program Execution AttributesProgram Execution Attributes

YesNo NoNeed printer?

NoYesNo Need terminal?

YesNoNoNeed disk?

80K100K50KMemory required

10 min15 min5 minDuration

Heavy I/OHeavy I/OHeavy computeType of jog

JOB3JOB2JOB1



10 min18 min Mean response time

12 jobs/h6 jobs/hThroughput rate

15 min30 minElapsed time

67%33%Printer use

67%33%Disk use

67%30%Memory use

33%17%Processor use

MultiprogrammingUniprogramming

Effects of MultiprogrammingEffects of Multiprogramming Operation System OverviewOperation System Overview


UniprogrammingUniprogramming UtilizationUtilization Operation System OverviewOperation System Overview


Multiprogramming UtilizationMultiprogramming Utilization Operation System OverviewOperation System Overview


• User interface acts directly with the computer• Such as transaction processing, an interactive

mode is essential• Multiprogramming can be used handle multiple

interactive jobs

TimeTime--Sharing SystemsSharing Systems Operation System OverviewOperation System Overview

Command entered at the terminal

Job control language instructions provided with the job

Source of instructions to operating system

Minimize response timeMaximize processor usePrincipal objective

Time SharingBatch Multiprogramming


• Process – A program in execution– The “animated spirit”of a program– That entity to which a processor is assigned

SchedulingScheduling SchedulingScheduling

The decision as to which process’s pending I/O request shall be handled by an available I/O deviceI/O scheduling

The decision as to which available process will be executed by the processor

Short-term scheduling

The decision to add to the number of processes that are partially or fully in main memory

Medium-term scheduling

The decision to add to the pool of processes to be executed

Long-term scheduling


• Determines which programs are admitted to the system for processing

• Controls the degree of multiprogramming• Once admitted, a job or user program

becomes a process and is added to the queue for the short-term scheduler

• Newly created process begins in a swapped-out condition, in which case it is added to a queue for the medium-term scheduler

• Decides that the operating system can take on one or more additional processes

• Decides which job or jobs to accept and turn into processes

Long Term SchedulingLong Term Scheduling SchedulingScheduling


• Part of the swapping function• Swapping-in decision is based on the need

to manage the degree of multiprogramming• On a system that does not use virtual

memory, memory management is also an issue

MediumMedium--Term SchedulingTerm Scheduling SchedulingScheduling


• Dispatcher• Fine-grained decision of which job to execute

next

ShortShort--Term SchedulingTerm Scheduling SchedulingScheduling


• State – Status at any point in time– Used because it connotes that certain information

exists that defines the status at that point– New

• Program is admitted by the high-level scheduler but is not yet ready to execute

– Ready• Process is ready to execute

– Running• Process is being executed

– Waiting• Process is suspended

– Halted

Process StatesProcess States SchedulingScheduling


FiveFive--State Process ModelState Process Model SchedulingScheduling


Process Control BlockProcess Control Block• Identifier• State• Priority• Program Counter• Memory pointers• Context data

– Present in registers in the processor

• I/O status information• Accounting information

SchedulingScheduling

identifieridentifier

StateState

PriorityPriority

Program counterProgram counter

Memory PointerMemory Pointer

Context DataContext Data

I/O StatusI/O StatusInformationInformation

AccountingAccountingInformationInformation

..

..


Scheduling TechniquesScheduling Techniques• Begin at a point in time process A is running• The processor is executing instructions from

the program contained in A’s memory• The processor ceases to execute instructions

in A and begins executing instructions• Three reasons

– Process A issues a service call to the OS– Process A causes an interrupt– Some event unrelated to process A that requires

attention causes an interrupt



Scheduling ExampleScheduling Example SchedulingScheduling


OS QueueOS Queue• Long-term Queue

– List of jobs waiting to use the system– High-level scheduler will allocate memory and create a

process for one of the waiting items

• Short-term Queue– All processes in the ready state– One of these process could use the processor next– Priority levels may also be used

• I/O Queue– I/O queue for each I/O device– More than one process may request the use of the

same I/O device



OS for MultiprogrammingOS for Multiprogramming SchedulingScheduling


Queuing Diagram RepresentationQueuing Diagram Representation SchedulingScheduling


Memory ManagementMemory Management• In a uniprogramming system,

– Main memory is divided into two parts: • The operating system(resident monitor)• The program currently being executed

• In a multi programming system,– The “user”part of memory is subdivided to

accommodate multiple processes

• The task of subdivision is carried out dynamically by the OS and is known as memory management

Memory managementMemory management


SwappingSwapping• I/O activities are much slower than

computation and therefore the processor in a uniprogramming system is idle most of the time

• Main memory could be expanded and so be able to accommodate more processes

• 2 Flaws– First, main memory is expensive– Second, the appetite of programs for memory has

grown as fast as the cost of memory has dropped

• The solution is swapping



SwappingSwapping• Long-term queue of process requests,

typically stored on disk• These are bought in, one at a time, as space

becomes available• Rather than remain idle, the processor swaps

one of these processes back out to disk into an intermediate queue

• This is a queue of existing processes that have been temporarily kicked out of memory

• OS brings in another process form the interface another process form the intermediate queue



SwappingSwapping

• Swapping is an I/O operation, therefore there is the potential for making the problem worse, not better

• Because disk I/O is generally the fastest I/O on a system(compared with tape or printer I/O), swapping will usually enhance performance



Use of SwappingUse of Swapping Memory managementMemory management

((a)Sample Job Schedulinga)Sample Job Scheduling


Use of SwappingUse of Swapping Memory managementMemory management

((b)Swappingb)Swapping


PartitioningPartitioning• Simplest scheme for partitioning available

memory is to use fixed-size partitions• Although the partitions are of fixed size, they

need not be of equal size• When a process is brought into memory, it is

placed in the smallest available partition that will hold it

• Even with the use of unequal fixed-size partitions, there will be wasted memory



Fixed PartitioningFixed Partitioning Memory managementMemory management

(a)Equal-size partitions


(b)Unequal-size partitions

Fixed PartitioningFixed Partitioning Memory managementMemory management


PartitioningPartitioning• More efficient approach is to use variable-size

partitions• Allocated exactly as much memory as it

requires• Memory becomes more and more fragmented,

and memory utilization declines• Compaction

– Operating system shifts the processes in memory to place all the free memory together in one block

– This is a time-consuming procedure, wasteful of processor time



Effect of Dynamic PartitioningEffect of Dynamic Partitioning Memory managementMemory management


• The process is not likely to be loaded into the same place in main memory each time it is swapped in

• If compaction is used, a process may be shifted while in main memory

• The process in memory consists of instruction plus data

• The instructions will contain addresses for memory locations of two types– Addresses of data items– Addresses of instructions used for branching

instruction

PartitioningPartitioning Memory managementMemory management


PartitioningPartitioning• Addresses are not fixed• They will change each time a process is

swapped in• To solve this problem, a distinction is made

between logical addresses and physical addresses– Logical address

• A location relative to the beginning of the program– Physical address

• Actual location in memory

• Automatically converts from logical to physical address



PagingPaging• Memory is partitioned into equal fixed-size

chunks• Chunk of a program, known as pages, could

be assigned to available chunks of memory, known as frames, or page frames

• Wasted space in memory for that process is a fraction of the last page

• The list of free frames is maintained by the operating system



Allocation of Free FramesAllocation of Free Frames Memory managementMemory management


Paging Paging • The OS maintains a page table for each

process• The page table show the frame location for

each page of the process• Main memory is divided into many small

equal-size frames• Each process is divided into frame-size pages• Smaller processes require fewer pages, larger

processes require more



Logical and Physical AddressesLogical and Physical Addresses Memory managementMemory management


Virtual MemoryVirtual Memory Memory managementMemory management

• Demand Paging• Page Table Structure


• Each page of a process is brought in only when it is needed(on demand)

• If the program branch to an instruction on a page not in main memory, if the program references data on a page not in memory, a page fault is triggered

• Only a few pages of any given process are in memory

• When it brings one page in, it must throw another page out

• Thrashing– Processor spends most of its time swapping pages

rather than executing instructions

Demand PagingDemand Paging Memory managementMemory management


Demand PagingDemand Paging• Operating system tries to guess, based on

recent history, which pages are least likely to be used in the near future

• It is possible for a process to be larger than all of main memory

• Because a process executes only in main memory, that memory is referred to as real memory

• Programmer or user perceives a much larger memory – that which is allocated on the disk

• Virtual memory



Page Table StructurePage Table Structure• The basic mechanism for reading a word from

memory involves the translation of a virtual, or logical, address, consisting of frame number and offset, into a physical address, consisting of frame number and offset, using a page table

• The page number is used to index that table and look up the corresponding frame number

• The page number portion is mapped into a hash table using a simple hashing function

• The hash table contains a pointer to inverted page table, which contains the page table entries



Inverted Page Table StructureInverted Page Table Structure Memory managementMemory management


Translation Translation LookasideLookaside Buffer Buffer • Two physical memory accesses

– Fetch the appropriate page table entry– Fetch the desired data

• The straightforward virtual memory scheme would have the effect of doubling the memory access time

• Cache functions as a memory cache and contain page table entries that have been most recently used



Translation Translation LookasideLookaside Buffer Buffer • A virtual address is in the form of a page

number, offset• The memory system consults the TLB to

see if the matching page table entry is present

• If it is, the real address is generated by combining the frame number with the offset

• If not, the entry is accessed from a page table



Operation of Paging and TLBOperation of Paging and TLB Memory managementMemory management


LookasideLookaside Buffer and CacheBuffer and Cache•



SegmentationSegmentation• Visible to the programmer • Provided as a convenience for organizing

programs and data• Associating privilege and protection attributes

with instructions and data• Advantages

– Simplify the handling of growing data structure– Allow programs to be altered and recompiled

independently– Lend itself to sharing among processes– Lend itself to protection



PentiumIIPentiumII Memory ManagementMemory Management• Address Spaces

– Unsegmented unpaged memory– Unsegmented paged memory– Segmented unpaged memory– Segmented paged memory

• Segmentation– Table Indicator– Segment number– Request privilege level(RPL)

• Paging

PentiumIIPentiumII&PowerPC &PowerPC Memory ManagementMemory Management


PentiumIIPentiumII Memory ManagementMemory Management PentiumIIPentiumII&PowerPC &PowerPC Memory ManagementMemory Management



PentiumIIPentiumII Memory ManagementMemory Management


PentiumIIPentiumII Memory ParameterMemory Parameter PentiumIIPentiumII&PowerPC &PowerPC Memory ManagementMemory Management


Memory Address Translation(PII)Memory Address Translation(PII) PentiumIIPentiumII&PowerPC &PowerPC Memory ManagementMemory Management


PowerPC MemoryPowerPC Memory--ManagementManagement• Comprehensive set of addressing mechanism• Block address translation• Address one drawback of paging mechanism• Block addressing enable the map four large

blocks of instruction memory and four large block of data memory in a way that bypass the paging mechanism



Memory Management(PPC32bit) Memory Management(PPC32bit) PentiumIIPentiumII&PowerPC &PowerPC Memory ManagementMemory Management


PowerPC Address TranslationPowerPC Address Translation PentiumIIPentiumII&PowerPC &PowerPC Memory ManagementMemory Management


PowerPC Memory ManagementPowerPC Memory Management PentiumIIPentiumII&PowerPC &PowerPC Memory ManagementMemory Management

chapter 7 operating system support - yonsei...

Documents