TDDI04
Concurrent Programming,
Operating Systems,
and Real-time Operating Systems
Contents
[SGG7] Chapter 1
§ What Operating Systems Do
§ Computer System Organization and Architecture
•
CPU – I/O Interaction, Interrupts, Memory hierarchy
§ Operating System Operations
Introduction
•
•
n Overview of the major operating systems components
Traps / system calls, Dual-mode, Timer
Process and memory management
§ Computing Environments
•
•
n Coverage of basic computer system organization
Copyright Notice: The lecture notes are mainly based on Silberschatz’s, Galvin’s and Gagne’s book (“Operating System
Concepts”, 7th ed., Wiley, 2005). No part of the lecture notes may be reproduced in any form, due to the copyrights
reserved by Wiley. These lecture notes should only be used for internal teaching purposes at the Linköping University.
Client-Server, Parallel and Distributed Systems
Special-Purpose Systems,
e.g. real-time / embedded systems
Acknowledgment: The lecture notes are originally compiled by C. Kessler, IDA.
Klas Arvidsson, IDA,
Linköpings universitet.
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What is an Operating System (OS)?
§ A program that acts as an intermediary
between a user of a computer
and the computer hardware.
Where are OSs found?
General purpose systems
Embedded systems
Microprocessor
market shares
in 1999
§ Operating system goals:
•
•
•
•
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99%
Execute user programs in a well-defined environment.
Make the computer system convenient to use.
1%
Administrate system resources.
Enable efficient use of the computer hardware.
§ An operating system provides an environment
within which other programs can do useful work;
the OS does not perform any “useful” function itself.
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Real-Time Operating Systems (RTOS)
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Operating Systems
General purpose operating systems
§ Unix
§ Sun Solaris
§ HP-UX
§ Linux
§ Windows 95/98/NT/2000/XP
§ Mac OS X
n Real-time system (RTS)
n Real-time constraints
n Hard RTS
n Safety critical applications (e.g. Drive-by-Wire)
n Soft RTS
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Application specific operating systems, e.g. real-time OS
§ OSE-Delta
§
§
§
§
VxWorks
Chorus
RT-Linux, RED-Linux
EPOC, RT-Mach ...
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1
Operating System Definition
Computer System Structure
§ OS is a resource allocator
•
•
Computer system
can be divided into 4 components:
Manages all resources of a computer system
§ Hardware
provides basic computing resources
Decides between conflicting requests
for efficient and fair resource use
•
§ OS is a control program
•
Controls execution of programs
to prevent errors and improper use of the computer
§ No universally accepted definition
§ “The one program running at all times on the computer”
is called the kernel.
Everything else is either a system program (ships with the
operating system) or an application program.
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CPU, memory, I/O devices
§ Operating system
controls and coordinates use of hardware
among various applications and users
© Silberschatz, Galvin and Gagne 2005
§ Application programs
define the ways in which the system resources are used
to solve the computing problems of the users
•
Word processors, compilers, web browsers, database systems, games
§ Users
•
People, machines, other computers
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Computer System Organization
CPU – I/O Device Interaction (1)
§ Computer-system operation
§ I/O devices and the CPU can execute concurrently.
•
One or more CPUs, device controllers connected through
common bus providing access to shared memory
§ Each device controller has a local buffer.
•
Concurrent execution of CPUs and devices,
competing for memory cycles
§ I/O is from the device to local buffer of controller.
§ CPU moves data from/to main memory to/from local buffers
§ Device controller informs CPU that it has finished its operation
by causing
an interrupt.
Remark:
Alternative to
interrupt usage:
Polling / Busywaiting, see
[SGG7] Ch. 13.2.1
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I/O Interaction using Interrupt
CPU – I/O Device Interaction (2)
§ Example: Read from the keyboard (KBD)
§ DMA = Direct Memory Access
•
allows for parallel activity of CPU and I/O data transfer
System Bus
CPU + Memory
0: initiate I/O operation KBD_RD
Memory
Device
controller
OS Kernel
3:
ISR table
ISR’s
...
Device
5:
Device driver 1
...
Device driver
KBD
4:
...
A OS buffer
User program code
2: data
+ signal interrupt for KBD_RD
A
Local buffer
1:
token
1
4
2
3
3: call ISR for KBD_RD
4: ISR uses device driver KBD,
passes data to an OS buffer
5: return from interrupt
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Interrupt (1)
Interrupt (2)
§ Interrupt transfers control to an interrupt service routine,
generally through the interrupt vector (IRV), a branch table that
contains the start addresses of all the service routines.
§ A trap is a software-generated interrupt
caused either by an error or a user request.
• Examples:
Division by zero;
Request for OS service
§ An operating system is interrupt driven.
§ The OS preserves the state of the CPU
by saving registers and the program counter.
§ Interrupt architecture must save the address of the interrupted
instruction.
§ How to determine which type of interrupt has occurred?
•
•
polling
vectored interrupt system:
interrupt number ©indexes
IRV
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Interrupt Timeline
Storage Hierarchy
for a single process doing output
§ Storage systems
organized in hierarchy.
•
•
•
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Speed
Cost
Volatility
§ Caching –
keeping copies of some data temporarily in faster but smaller
storage, closer to CPU
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Background: Storage Hierarchy
Level
1
2
3
Name
Registers
Cache
Main memory Flash
memory
Disk storage
Size
< 1 KB
< 16 MB
< 16 GB
< 64 GB
500 GB
Technology
Custom
memory with
multiple
ports, CMOS
On-chip /
off-chip
CMOS
SRAM
CMOS
DRAM
NAND
Flash
Magnetic disk
(mechanical)
Access (ns)
0.25 – 0.5
0.5 – 25
10 – 80
100-200
>5000
Bandwidth
(MB/s)
20-100K
5-10K
1-5K
10-100
20-150
3-4
4
Managed by Compiler
Hardware Operating
system
Operating
system
Operating
system
Backed by
Main
memory
Depends
on usage
Optical storage
or tape
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Disk, flash
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Background: Caching
Performance of various levels of storage:
Cache
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§ Important principle, performed at many levels in a computer
(in hardware, operating system, software)
§ Information in use copied from slower to faster storage
temporarily
§ Faster storage (cache) checked first to determine if
information is there
•
•
If it is, information used directly from the cache (fast)
If not, data copied to cache and used there
§ Cache smaller than storage being cached
•
•
Cache management important design problem
Cache size and replacement policy
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Memory Consistency Problems
Operating System Operations
§ Multitasking environments must be careful to use the most recent value,
no matter where it is stored in the storage hierarchy
§ Dual mode, system calls
§ CPU management
•
•
Example: Migration of integer A from disk to register creates 3 copies
§ Multiprocessor environment must provide cache coherency in hardware
such that all CPUs have the most recent value in their cache
•
Uniprogramming, Multiprogramming, Multitasking
Process management
§ Memory management
§ File system and mass storage management
§ Protection and security
More on this in TDDC78 – Programming parallel computers
§ Distributed environment situation even more complex
•
•
Similar consistency problem: Several copies of a datum can exist
Various solutions exist, covered in [SGG7] Chapter 17, and TDDB37
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Dual mode, System calls
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Uniprogramming
§ Dual-mode operation
allows OS to protect itself and other system components
•
User mode and kernel mode (supervisor mode, privileged mode)
Running
> Privileged instructions only executable in kernel mode
> System call changes mode to kernel, on return resets it to user
•
Mode bit provided by hardware
0
Running
Waiting
10
110
Waiting
120
220
Process execution time:
CPU:
10 + 10 time units
I/O:
100 + 100 time units
I.e., I/O intensive (200/220 = 90.9%), CPU utilization 9.1%
Lecture 2 on System calls and OS structures
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Single user with single program
cannot keep CPU and I/O devices busy at all times.
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Multiprogramming
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Multiprogramming with three programs
§ needed for efficiency
•
Multiprogramming organizes jobs
(code and data)
so CPU always has one to execute
•
A subset of total jobs in system
is kept in memory
•
One job selected and run
via job scheduling
•
A
Running
B
Running
C
When it has to wait (e.g., for I/O),
OS switches to another job
Running
Waiting (printer)
Waiting (disk)
Waiting
Running
Running Waiting (network)
Waiting
Running
Waiting
Running Running Running Waiting Running Running Running Waiting
combined
Memory layout for multiprogrammed system
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Timesharing (Multitasking)
CPU time sharing using timer interrupt
§ extension of multiprogramming:
CPU switches jobs so frequently that users can interact with
each job while it is running
§ Timer to prevent infinite loop / process hogging resources
•
For interactive computer systems,
the response time should be short (< 1 second)
•
Each user has at least one program executing in memory
processes
•
If several jobs ready to run at the same time
CPU scheduling
•
If processes don’t fit in memory,
swapping moves them in and out to run
•
Virtual memory allows execution of processes not
completely in memory
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•
•
•
•
Set up to interrupt the computer after specific period
System decrements counter at clock ticks
When counter = zero, generate an interrupt
So, OS regains control and can reschedule or terminate a
program that exceeds allotted time
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Process Management
Process Management Activities
§ A process is a program in execution.
• A unit of work within the system.
• Program is a passive entity, process is an active entity.
§ Process needs resources to accomplish its task
The operating system is responsible for:
•
•
§
§
§
§
CPU, memory, I/O, files
Initialization data
Process termination requires reclaim of any reusable resources
Single-threaded process: has one program counter
specifying location of next instruction to execute
• Process executes instructions sequentially, one at a time, until
completion
Multi-threaded process: has one program counter per thread
Typically, a system has many processes (some user, some system pr.)
running concurrently on one or more CPUs
• Concurrency by multiplexing the CPUs among the processes / threads
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§ Creating and deleting both user and system processes
§ Suspending and resuming processes
§ Providing mechanisms for process synchronization
§ Providing mechanisms for process communication
§ Providing mechanisms for deadlock handling
Lecture on Processes and Threads
Lecture on CPU Scheduling
Lecture on Synchronization
Lecture on Deadlocks
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Memory Management
Mass-Storage Management (1)
§ Memory: A large array of words or bytes, each with its own address
• Primary storage – directly accessible from CPU
• shared by CPU and I/O devices
• a volatile storage medium
§ Disks used to store data that do not fit in main memory or
data that must be kept for a “long” period of time.
•
•
All data in memory before and after processing
All instructions in memory in order to execute
§ Memory management determines what is in memory when.
• Optimizing CPU utilization and memory utilization
§ OS memory management activities
• Keeping track of which parts of memory are currently being used
and by whom
• Deciding which processes (or parts thereof) and data to move
into and out of memory
•
Allocating and deallocating memory space as needed
Lectures on Virtual Memory and Memory Management
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• Secondary storage
§ OS activities:
•
•
•
Free-space management
Storage allocation
Disk scheduling
§ Critical for system performance
§ Some storage need not be fast
• Tertiary storage
optical storage, magnetic tape...
• Still must be managed
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Mass-Storage Management (2)
Protection and Security
§ OS provides uniform, logical view of information storage
•
•
Abstracts from physical to logical storage unit: file
Each medium (disk, tape) has different properties:
access speed, capacity, data transfer rate, sequential/random access
§ Protection – any mechanism for controlling access of processes or users
to resources defined by the OS
§ Security – defense of the system against internal and external attacks
•
§ OS File-System management
• Files usually organized into directories
• Access control
• OS activities include
> Creating and deleting files and directories
Huge range, including denial-of-service, worms, viruses, identity theft,
theft of service
§ Systems generally first distinguish among users,
to determine who can do what
•
•
•
> Primitives to manipulate files and directories
> Mapping files onto secondary storage
User identities (user IDs, security IDs)
associated with all files, processes of that user
Group identifier (group ID)
> Backup files to tertiary storage
Lecture on Protection and Security
Lecture on File Systems
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Computer Systems and Environments
Stand-alone desktop computer
§ Stand-alone desktop computer
§ Blurring over time
§ Client-server systems
§ Office environment
§ Parallel systems
•
PCs connected to a network,
terminals attached to mainframe, or
minicomputers providing batch and timesharing
•
Now portals allowing networked and remote systems
access to same resources
§ Distributed systems
§ Peer-to-Peer computing systems
§ Real-time systems
§ Handheld systems
§ Home networks
§ Embedded systems
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•
Used to be single system,
then modems
•
Now firewalled, networked
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Client-Server Computing
Parallel Systems (1)
§ Servers respond to requests by clients
• Remote procedure call –
also across machine boundaries via network
§ Compute server:
compute an action requested by the client
§ File server:
Interface to file system (read, create, update, delete)
§ Multiprocessor systems with more than one CPU in close communication.
• Soon the default, even for desktop machines (multi-core / CMP)
§ Tightly coupled system (aka. shared-memory system, multiprocessor)
• processors share memory and a clock;
• communication usually takes place through the shared memory.
§ Advantages of parallel systems:
• Increased throughput
•
•
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Economical
> Scalability of performance
> Multiprocessor system vs multiple single-processor system
(reduction of hardware such as disks, controllers etc)
Increased reliability
> graceful degradation (fault tolerance, …)
> fail-soft systems (replication, …)
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Parallel Systems (2)
Parallel Systems (3)
SMP
architecture
§ Symmetric multiprocessing (SMP)
•
•
•
Each processor runs an identical copy of the operating system.
Many processes can run at once without performance deterioration.
Most modern operating systems support SMP
§ Asymmetric multiprocessing
•
Each processor is assigned a specific task;
a master processor schedules and allocates work to slave processors.
•
More common in special-purpose systems (e.g., embedded MP-SoC)
Remark: the notion of “processor” is relative:
A traditional PC is normally considered to only have one CPU, but it usually has a
graphic processor, a communication processor etc, and this is not considered a
multi-processing system.
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§ Speed-up of a single application by parallel processing?
• Requires parallelisation / restructuring of the program
• Or explicitly parallel algorithms
• Used in High-Performance Computing
for numerically intensive applications
(weather forecast, simulations, ...)
§ Multicomputer
(”distributed memory parallel computer”)
• loosely coupled
•
•
•
More in TDDC78 – Programming parallel computers
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Distributed Systems (1)
Distributed Systems (2)
§ Loosely coupled system
§ Network Operating System
•
•
each processor has its own local memory
processors communicate with one another through various
communications lines, such as high-speed buses or
telephone lines (LAN, WAN, MAN, Bluetooth, …).
§ Distribute the computation among several physical
processors.
•
•
•
© Silberschatz, Galvin and Gagne 2005
provides file sharing, e.g., NFS - Network File System
provides communication scheme
runs independently from other computers on the network
§ Distributed Operating System
•
•
§ Advantages of distributed systems:
•
•
•
•
NSC Monolith
can be a more economic and scalable alternative to SMP’s
but more cumbersome to program (message passing)
Example: ”Beowulf clusters”
Resource sharing
Computation speed up
Adaptivity: load sharing (migration of jobs)
less autonomy between computers
gives the impression there is a single operating system
controlling the network.
More about this in TDDB37 Distributed Systems
Fault tolerance
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Real-Time Systems
§ Often used as a control device in a dedicated application such as
controlling scientific experiments, medical imaging systems, industrial
control systems, and some display systems.
§ Well-defined tasks with fixed time constraints.
§ Hard real-time systems.
• Conflicts with time-sharing systems,
not supported by general-purpose OSs.
T D D B63 – Op erating Sy s tem C on ce pts –
A. B e dna rsk i
§ Soft real-time systems
• Limited utility in industrial control or robotics
• Useful in applications (multimedia, virtual
reality) requiring advanced OS features.
Lecture on Real-time Operating Systems
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