Transcript CS4023 * Operating Systems

CS4023 – Operating Systems
Dr. Atif Azad
[email protected]
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Example: What’s in a Search Query?
DNS
Servers
DNS
request
Datacenter
create
result
page
Search
Index
Page
store
Load
balancer
Ad Server
• Complex interaction of multiple components in multiple
administrative domains
– Systems, services, protocols, …
Adapted from https://cs162.eecs.berkeley.edu/static/lectures/1.pdf (c) UC Berkeley 2015
Operator …
Switchboard Operator
Computer Operators
Adapted from https://cs162.eecs.berkeley.edu/static/lectures/1.pdf (c) UC Berkeley 2015
Why Study Operating Systems?
• Design Operating Systems
• Learn how to build complex systems:
– How can you manage complexity for future projects?
• Almost everyone of you will write applications that utilise operating systems
– understanding operating systems concepts can help you write better applications
– some times, you may even have to replicate Operating Systems concepts (e.g. XBox)
• Engineering issues:
– Why is the web so slow sometimes? Can you fix it?
– What features should be in the next mars Rover?
– How do large distributed systems work? (Skype, etc)
• Buying and using a personal computer:
– Why different PCs with same CPU behave differently (Opteron, Itanium, Celeron,
Pentium)?
– What is different among Windows XP, 2000, Linux, Mac OS …?
• Business issues:
– Should your organisation buy thin-clients vs PC?
• Security, viruses, and worms
– What exposure do you have to worry about?
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Goals for This Week
• Why Operating Systems?
• What is an Operating System?
• How does this class operate?
Interactive is important!
Ask Questions!
Acknowledgement
• Significant material in this set of lectures has
been borrowed from:
– http://www.cs.berkeley.edu/~kubitron/courses/cs162
/. Copyright © 2010 UCB
– https://cs162.eecs.berkeley.edu/ Copyright © 2015
UCB
– http://www.os-book.com . © 2005 Silberschatz et al.
– Dr Patrick Healy at CSIS Department, University of
Limerick.
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Class Website
• http://amnesia.csisdmz.ul.ie/4023/
• Primary source of information about the
module.
– Grading policy
– Tutorial exercises
– Lab exercises
– Course material
– Grades
– Extra Reading Material
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Course Material
• Silberschatz, Galvin & Gagne Operating System
Concepts (Wiley) 9th Edition.
– Check with the University Book Shop
– On SL in library (ed.s 6 & 8) http://www.os-book.com/
– Chapters 1 – 8 (tentatively). Look up Review Questions and
Practice Exercises at the end of the chapter.
– Read both lecture material and the book.
• Lab Exercises
• Tutorials
• Extra Reading Material (mandatory)!
– Except where stated otherwise.
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Grading Policy and How to Help
Yourself
• Check Grading Policy at the website:
http://amnesia.csisdmz.ul.ie/4023/
• Attendance: Mandatory! First 5 minutes rule.
– Applies to labs, lectures and tutorials.
• The module is demanding ~ 10 hours/week
– But extra credit also available
– Check Study Advice on the class website.
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Study in Groups
• Your attention spans are not the same
– Share notes
• Can face your weak points (more likely to come
up in groups)
• Teaching is great for self learning
• Communication is key in job environment
• Advice on how to make effective groups:
– http://www.topuniversities.com/blog/joining-studygroup-benefits
– Google is your friend!
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Labs
• Will be supervised by a TA.
• lab exercise is due this week.
– Log into your linux accounts
– And read the instructions on the class website.
• No login account? Give your ID, Name, Course Code to
your TA.
• Programming lab exercises begin later - worth 20%.
– All in C language.
– Learn C mostly through self-help! start NOW!
– Get books or consult online tutorials
• http://www.cprogramming.com/begin.html
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Tutorials
• Tutorials start this week
– Attempt exercises BEFORE coming to tutorials
• except in the first week - introductory session
– Hand in your attempt to TA to be marked present
– Inform the TA about most difficult questions at the
start of the session;
• not enough time to solve all questions in a tutorial
session
– Tutorial exercises deliberately long to cover most
material and prepare you for exam.
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Material Availability
• Labs/tutorial exercises - uploaded by Friday
evening each week.
– check the class website each Friday evening.
• Lecture slides:
– uploaded at the start of each week
– will contain stuff for both lectures of the week
• but may be revised before the second lecture
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Technology Trends: Moore’s Law
Moore’s Law
2X transistors/Chip Every 1.5 years
Gordon Moore (co-founder of
Intel) predicted in 1965 that the
transistor density of
semiconductor chips would
double roughly every 18 months.
Called “Moore’s Law”
Microprocessors have
become smaller, denser,
and more powerful.
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People-to-Computer Ratio Over Time
From David Culler
• Today: Multiple CPUs/person!
– Approaching 100s?
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New Challenge: Slowdown in Joy’s law
of Performance
Performance (vs. VAX-11/780)
10000
From Hennessy and Patterson, Computer Architecture: A
Quantitative Approach, 4th edition, Sept. 15, 2006
3X
??%/year
1000
52%/year
100
10
25%/year
 Sea change in chip
design: multiple “cores” or
processors per chip
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1978 1980 1982 1984 1986 1988 1990 1992 1994 1996 1998 2000 2002 2004 2006
• Y-axis counts the clock speed (MHz). Notice the log scale
• We do not have a 10 GHz processor!
• Can not make the single processor much faster
Adapted from https://cs162.eecs.berkeley.edu/static/lectures/1.pdf (c) UC Berkeley 2015
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The power density wall
• If Moore’s law continues to power a single
processor, incredible heat generates.
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Adapted from https://cs162.eecs.berkeley.edu/static/lectures/1.pdf (c) UC Berkeley 2015
Way forward
• Can not expect the single processor to increase
performance.
– No free lunch (not anymore!)
• Redesign of hardware
– Multiprocessing systems
• Implications
– Redesign of software (both applications and Operating
Systems).
– Increasing complexity of software systems
• Recommended reading:
– The death of scaling
– The Free Lunch is Over: A Fundamental Turn towards
Concurrency in Software
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Computer System Organization
Book Section 1.2
• Computer-system operation
– One or more CPUs, device controllers
connect through common bus providing
access to shared memory
– Concurrent execution of CPUs and devices
competing for memory cycles
Bus
RAM
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Computer-System Operation
• I/O devices and the CPU can
execute concurrently
• Each device controller is in charge
of a particular device type
• I/O is from the device to local
buffer of controller
– Why local buffer?
• Device controller informs CPU that
it has finished its operation by
causing an interrupt
• CPU moves data from/to main
memory to/from local buffers
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I/O Structure and Interrupts
Book section 1.2.3
• Device controllers (DC) (hardware) handle devices.
– Contains memory: registers and local buffer.
• OS talks to DC through Device Drivers (DD)
(software)
• I/O begins:
– DD loads registers to indicate what is required.
– DC reads registers to decide what to do (read from KB)
– DC transfers data: device to/from local buffer.
– End of transfer: DC indicates to DD via an interrupt.
– OS transfers data from local buffer to memory, and
returns the address of that data.
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Interrupt Timeline
Time
• Repeated, small data I/O can slow things down
• Direct Memory Access (such as disk copying).
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Direct Memory Access (DMA)
• Instead of generating one interrupt per byte of
data:
– Copy the whole block of data from the buffer to main
memory and then interrupt the CPU.
• High speed I/O
• Note: for programmers:
– Avoid repetitive I/O in your programs.
– Can slow things down
– Java provides Buffered readers and writer classes.
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Example: Some Mars Rover
(Pathfinder) Requirements
Program loaded
into memory for
• Pathfinder hardware limitations/complexity:
execution
– cameras, scientific instruments, batteries,
solar panels, and locomotion equipment
– Many independent processes work together
• Can’t hit reset button very easily!
– Must reboot itself if necessary
– Must always be able to receive commands from Earth
• Individual Programs must not interfere
– E.g. camera’s software should not crash antenna
positioning software!
• Further, all software may crash occasionally
– Automatic restart with diagnostics sent to Earth
– Periodic checkpoint of results saved?
• Certain functions time critical:
– Need to stop before hitting something
– Must track orbit of Earth for communication
Increasing Software Complexity
Windows 7
From MIT’s 6.033 course
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How do we tame complexity?
• Every piece of computer hardware different
– Different CPU
• Pentium, PowerPC, ColdFire, ARM, MIPS
– Different amounts of memory, disk, …
– Different types of devices
• Mice, Keyboards, Sensors, Cameras, Fingerprint readers
– Different networking environment
• Cable, DSL, Wireless, Firewalls,…
• Questions:
– Does the programmer need to write a single program that
covers all operations of computer systems? Modularity?
– Does every program have to be altered for every piece of
hardware? Re-usability?
– Does a faulty program crash everything? Fault isolation?
– Does every program have access to all hardware? Security?
OS Tool: Virtual Machine
Abstraction
Application
Operating System
Hardware
Virtual Machine Interface
Physical Machine Interface
•
•
•
•
Build in layers
OS sits on top of Hardware
Applications run on top of OS
Easier programming: do not need to understand hardware in detail to write an
application program.
• Hardware is much harder to deal with: e.g. imagine sending an email from a
computer that has no OS.
– Optimize for convenience, utilization, security, reliability, etc…
• Instead understand interfaces
– What’s the hardware interface? (Designing OS?)
– What’s the application interface? (Writing a Software Application e.g. your lab
exercise)
Virtual Machines
• Software emulation of an abstract machine
– Make it look like hardware has features you want
– Programs from one hardware & OS on another one
• Programming simplicity
–
–
–
–
Each process thinks it has all memory/CPU time
Each process thinks it owns all devices
Different Devices appear to have same interface
Device Interfaces more powerful than raw hardware
• Bitmapped display  windowing system
• Ethernet card  reliable, ordered, networking (TCP/IP)
• Fault Isolation
– Processes unable to directly impact other processes
– Bugs cannot crash whole machine
• Protection and Portability
– Java interface safe and stable across many platforms.
– JVM is NOT an operating system though!
Book section
1.11.6
Virtual Machines: Layers of OSs
• Useful for OS development
– When OS crashes, restricted to one VM
– Can aid testing programs on other OSs
Virtual Machine Managers
• VMware :
http://www.vmware.com/download/player/)
– see section 1.12.2 on installing it
– Commercial Software
•
Book section
1.12.2
VirtualBox (https://www.virtualbox.org)
– See
http://people.westminstercollege.edu/faculty/ggagne
/osc/vm/index.html
– Instructions on how to install linux on top of virtual
box.
– Recommended for the book.
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So, What is an Operating System?
• No Universal Definition, but a general
understanding.
Book section
1.1
– A program that acts as an intermediary
between a user of a computer and the
computer hardware
– What does it do? That depends upon your point
of view, which in turn depends on the
components of Computer System.
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User’s View: What an OS does.
• Personal computer users want convenience, ease of
use and good performance
– Don’t care about resource utilization
• But do care in shared computer such as mainframe or
minicomputer must keep all users happy
• Also in workstations, with most individual resources
but some shared (servers)
• Handheld: convenience of use.
• Embedded computers: fridges, automobiles, washing
machines etc may have little to no user view.
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Computer System’s View: What an OS
Does
• Fair and Efficient Resource allocator:
– CPU time, memory, I/O devices etc to be used by
conflicting requests.
• Control Program
– Supervise proper execution of programs. Prevents
errors (such as one buggy program crashing the
system)
– Manages the operation of I/O devices (see section
1.2.3 for details)
• Like Government, facilitates the operation
– But does it do anything useful itself?
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Another View on What’s an OS
• “everything that the vendor ships when we order
an operating systems”.
• Contentious because it varies.
– Graphical User Interface? Is it a part of an OS?
• Not always.
– What about email programs? Or web browsers?
• Safari on iphone. Internet Explorer on Windows?
• A more accepted definition:
– A program that is running on the computer all the
time: Kernel.
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What is OS: summary
– A program that acts as an intermediary between a
user of a computer and the computer hardware
– A program that allocates computer resources such
as CPU time, memory and I/O access to all the
programs running, efficiently and fairly.
– A control program that supervises the execution
of everything on the computer: they should
execute correctly (as allowed by OS) and they
should not affect other programs (fault isolation)
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Fetch-Execute Cycle
• Process: Program loaded into the main memory (RAM)
• CPU fetches one instruction into instruction register at
a time and executes it.
• Execution:
– Decodes the instruction: may cause fetching operands
from memory.
– May store the result of execution back in the memory.
• Fetches next instruction and executes
– Interrupts cause instructions to be fetched from a different
sequence stored outside the executing program.
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Common Functions of Interrupts
Book Section 1.2
• Interrupt transfers control to the interrupt service
routine generally, through the interrupt vector, which
contains the addresses of all the service routines
• Interrupt architecture must save the address of the
interrupted instruction
• An operating system is interrupt driven
• Interrupts should be handled quickly.
• Types of interrupts:
– Hardware interrupt: a signal to CPU through system bus.
– Software interrupt:
• trap a special function call i.e. system call/monitor call
requesting an OS facility: print output, open a file etc.
• exception is a software-generated interrupt caused by an
error/abnormal execution: divide by zero, stepping in
debugging
Useful reading: http://flint.cs.yale.edu/cs422/doc/art-of-asm/pdf/CH17.PDF
Storage Structure
• Main memory – only large storage media that the CPU can
access directly
Section 1.2.2
– Random access
– Typically volatile
• Secondary storage – extension of main memory that provides
large nonvolatile storage capacity
• Hard disks – rigid metal or glass platters covered with
magnetic recording material
– Disk surface is logically divided into tracks, which are subdivided
into sectors
– The disk controller determines the logical interaction between
the device and the computer
• Solid-state disks – faster than hard disks, nonvolatile
– Various technologies e.g. a mixture of RAM and magnetic disk
– Becoming more popular (in cameras, PDAs, USB etc)
http://uk.pcmag.com/storage-devicesreviews/8061/feature/ssd-vs-hdd-whats-the-
Storage Hierarchy
• Storage systems organized in hierarchy
– Speed
– Cost
– Volatility
• Caching – copying information into faster
storage system; main memory can be viewed as
a cache for secondary storage
– Faster storage checked first. if info there use it, else
copy data into cache.
– Cache smaller than storage being cached. Thus
cache management is an important design
problem.
Storage-Device Hierarchy
Speed and Cost
Volatile