Download Operating Systems Overview An Operating System Performs

1/25/2010
Operating Systems
Overview
Intro, Sys Calls, Threads, etc.
Tarek Abdelzaher
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An Operating System Performs
Common Application Functions
Application Software
Web Server
Second Life
Yahoo
Chat
Pop Mail
Operating System
Read/Write
Hardware
Standard
Output
Device
Control
File
System
Communication
Network
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OS Exports a User Interface
Application Software
Web Server
Second Life
Yahoo
Chat
Pop Mail
Standard Operating System Interface
Operating System
Read/Write
Standard
Output
Device
Control
File
System
Hardware
Communication
Network
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Increase Portability =
Minimize Machine-Specific Code
Application Software
Web Server
Second Life
Yahoo
Chat
Pop Mail
Standard Operating System Interface
Operating System (machine independent part)
Read/Write
Standard
Output
Device
Control
File
System
Communication
Machine specific part
Hardware
Network
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Increase Portability =
Minimize Machine-Specific Code
Application Software
Second Life
Yahoo
Chat
Pop Mail
Standard Operating System Interface
Operating System (machine independent part)
Read/Write
Standard
Output
Device
Control
File
System
Communication
Portable
Web Server
Machine specific part
Network
Hardware
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OS Runs on Multiple Platforms
while Presenting same Interface
Application Software
Second Life
Yahoo
Chat
Pop Mail
Standard Operating System Interface
Operating System (machine independent part)
Read/Write
Standard
Output
Device
Control
File
System
Communication
Portable
Web Server
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OS Runs on Multiple Platforms
while Presenting same Interface
Application Software
Second Life
Yahoo
Chat
Pop Mail
Standard Operating System Interface
Operating System (machine independent part)
Read/Write
Standard
Output
Device
Control
File
System
Communication
Portable
Web Server
Machine specific part
Network
Hardware
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Linux
(The POSIX Standard)
Application Software
Second Life
Yahoo
Chat
Pop Mail
The POSIX Standard Specifies UNIX Interface
Operating System (machine independent part)
Read/Write
Standard
Output
Device
Control
File
System
Communication
Portable
Web Server
Machine specific part
Hardware
Network
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OS Goals

1) Provide an interface for applications to
do common functions.
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Software Layers:
Applications call Libraries
Application
Libraries (e.g., stdio.h)
Provided pre-compiled
Defined in headers
Input to linker (compiler)
Invoked like functions
May be “resolved” when
program is loaded
Portable OS Layer
Machine-dependent layer
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Software Layers:
Libraries make OS System Calls
Application
Libraries
Portable OS Layer
system calls (read, open..)
All “high-level” code
Machine-dependent layer
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Software Layers:
System Calls access Drivers, etc.
Application
Libraries
Portable OS Layer
Machine-dependent layer
Bootstrap
System initialization
Interrupt and exception
I/O device driver
Memory management
Kernel/user mode
switching
Processor management
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MP1

Familiarize yourself with installing/compiling
an OS and changing its interface (System
Calls)
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Steps in Making a System Call
read (fd, buffer, nbytes)
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Some System Calls For Process
Management
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Some System Calls For File
Management
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Some System Calls For Directory
Management
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Some System Calls For
Miscellaneous Tasks
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OS Goals

Provide an interface for applications to do
common functions.
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OS Goals


Provide an interface for applications to do
common functions.
Manage resources
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Managed Resources - CPU
CPU
Bus
Process/thread scheduling, context switching, etc.
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Managed Resource - Memory
CPU
Memory
Bus
Paging, swapping, virtual memory management, etc.
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Memory Hierarchy
faster
larger

Make it look like it’s as large as the disk and
as fast as the cache
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Managed Resource – I/O
CPU
Memory
I/O
Devices
Bus
Drivers, interrupts, timers, files, etc.
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OS Goals


Provide an interface for applications to do
common functions.
Manage resources
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OS Goals



Provide an interface for applications to do
common functions.
Manage resources
Structure concurrent application
execution
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Threads and Processes
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Things Suitable for threading





Block for potentially long waits
Use many CPU cycles
Respond to asynchronous events
Execute functions of different importance
Execute parallel code
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Thread Usage: Word Processor

What if it is single-threaded?
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Thread Usage: Web Server
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Common Multi-thread Software
Architectures

Manager/worker


Pipeline


a single thread, the manager assigns work to other
threads, the workers. Typically, the manager handles all
input and parcels out work to the other tasks
a task is broken into a series of sub-operations, each of
which is handled by a different thread. An automobile
assembly line best describes this model
Peer

similar to the manager/worker model, but after the main
thread creates other threads, it participates in the work.31
User-level Threads

Advantages

Fast Context Switching:




User level threads are implemented using user level thread
libraries, rather than system calls, hence no call to OS and no
interrupts to kernel
When a thread is finished running for the moment, it can call
thread_yield. This instruction (a) saves the thread information
in the thread table, and (b) calls the thread scheduler to pick
another thread to run.
The procedure that saves the local thread state and the scheduler
are local procedures, hence no trap to kernel, no context switch,
no memory switch, and this makes the thread scheduling very
fast.
Customized Scheduling
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Kernel-level Threads




Kernel can schedule threads in addition to
processes.
Multiple threads of a process can run
simultaneously on multiple CPUs.
Synchronization more efficient than for
processes (but less than for user-level
threads).
Kernel-level threads can make blocking I/O
calls without blocking other threads of same
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process
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