CS220 Course Overview CS220 : Computer Systems II 1 st Lecture

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CS220 Course Overview CS220 : Computer Systems II 1 st Lecture. Instructor: Nael Abu-Ghazaleh Slides credit: many slides due to R. Bryant, D. O’Halloran, T. Mowry , M. Sakr , K. Harras and many others. Overview. Syllabus, grading, mechanics Course theme Five realities
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CS220 Course OverviewCS220:Computer Systems II 1st LectureInstructor:Nael Abu-GhazalehSlides credit: many slides due to R. Bryant, D. O’Halloran, T. Mowry, M. Sakr, K. Harras and many othersOverview
  • Syllabus, grading, mechanics
  • Course theme
  • Five realities
  • How the course fits into the CScurriculum
  • Logistics
  • Course Theme:Abstraction Is Good But Don’t Forget Reality
  • Most CS courses emphasize abstraction
  • Abstract data types
  • Asymptotic analysis
  • These abstractions have limits
  • Especially in the presence of bugs
  • Need to understand details of underlying implementations
  • Useful outcomes from taking CS220
  • Become more effective programmers
  • Able to find and eliminate bugs efficiently
  • Able to understand security implications
  • Able to understand and tune for program performance
  • Prepare for later “systems” classes in CS
  • Compilers, Operating Systems, Networks, Computer Architecture, Embedded Systems, Storage Systems, etc.
  • Great Reality #1: Ints are not Integers, Floats are not Reals
  • Example 1: Is x2 ≥ 0?
  • Float’s: Yes!
  • Int’s:
  • 40000 * 40000 1600000000
  • 50000 * 50000 ??
  • Example 2: Is (x + y) + z = x + (y + z)?
  • Unsigned & Signed Int’s: Yes!
  • Float’s:
  • (1e20 + -1e20) + 3.14 3.14
  • 1e20 + (-1e20 + 3.14) ??
  • Source: xkcd.com/571Computer Arithmetic
  • Does not generate random values
  • Arithmetic operations have important mathematical properties
  • Cannot assume all “usual” mathematical properties
  • Due to finiteness of representations
  • Integer operations satisfy “ring” properties
  • Commutativity, associativity, distributivity
  • Floating point operations satisfy “ordering” properties
  • Monotonicity, values of signs
  • Observation
  • Need to understand which abstractions apply in which contexts
  • Important issues for compiler writers and serious application programmers
  • Ariane 5
  • French space program, costing 7 billion dollars culminated with a launch in 1996
  • Ariane 5 rocket crashed 40 seconds after launch
  • Software failure of inertial guidance system
  • Problem: converted a 64-bit floating value into a 16 bit integer
  • Overflow occurred, causing guidance to shutdown
  • Therac-25 x-ray machine
  • Great Reality #2: You’ve Got to Know Assembly
  • Chances are, you’ll never write programs in assembly
  • Compilers are much better & more patient than you are
  • But: Understanding assembly is key to machine-level execution model
  • Behavior of programs in presence of bugs
  • High-level language models break down
  • Tuning program performance
  • Understand optimizations done / not done by the compiler
  • Understanding sources of program inefficiency
  • Implementing system software
  • Compiler has machine code as target
  • Operating systems must manage process state
  • Creating / fighting malware
  • x86 assembly is the language of choice!
  • Great Reality #3: Memory MattersRandom Access Memory Is an Unphysical Abstraction
  • Memory is not unbounded
  • It must be allocated and managed
  • Many applications are memory dominated
  • Memory referencing bugs especially pernicious
  • Effects are distant in both time and space
  • Memory performance is not uniform
  • Cache and virtual memory effects can greatly affect program performance
  • Adapting program to characteristics of memory system can lead to major speed improvements
  • Memory Referencing Bug Exampledouble fun(inti){ volatile double d[1] = {3.14}; volatile long int a[2]; a[i] = 1073741824; /* Possibly out of bounds */ return d[0];}
  • Result is architecture specific
  • fun(0)  3.14fun(1)  3.14fun(2)  3.1399998664856fun(3)  2.00000061035156fun(4)  3.14, then segmentation faultMemory Referencing Bug Exampledouble fun(int i){ volatile double d[1] = {3.14}; volatile long int a[2]; a[i] = 1073741824; /* Possibly out of bounds */ return d[0];}fun(0)  3.14fun(1)  3.14fun(2)  3.1399998664856fun(3)  2.00000061035156fun(4)  3.14, then segmentation faultExplanation:Location accessed by fun(i)Memory Referencing Errors
  • C and C++ do not provide any memory protection
  • Out of bounds array references
  • Invalid pointer values
  • Abuses of malloc/free
  • Can lead to nasty bugs
  • Whether or not bug has any effect depends on system and compiler
  • Action at a distance
  • Corrupted object logically unrelated to one being accessed
  • Effect of bug may be first observed long after it is generated
  • How can I deal with this?
  • Program in Java, Ruby or ML
  • Understand what possible interactions may occur
  • Use or develop tools to detect referencing errors (e.g. Valgrind)
  • Great Reality #4: There’s more to performance than asymptotic complexity
  • Constant factors matter too!
  • And even exact op count does not predict performance
  • Easily see 10:1 performance range depending on how code written
  • Must optimize at multiple levels: algorithm, data representations, procedures, and loops
  • Must understand system to optimize performance
  • How programs compiled and executed
  • How to measure program performance and identify bottlenecks
  • How to improve performance without destroying code modularity and generality
  • Memory System Performance Example
  • Hierarchical memory organization
  • Performance depends on access patterns
  • Including how step through multi-dimensional array
  • void copyij(int src[2048][2048], int dst[2048][2048]){ int i,j;for (i = 0; i < 2048; i++)for (j = 0; j < 2048; j++) dst[i][j] = src[i][j];}void copyji(int src[2048][2048],int dst[2048][2048]){inti,j;for (j = 0; j < 2048; j++)for (i = 0; i < 2048; i++)dst[i][j] = src[i][j];}21 times slower(Pentium 4)The Memory MountainIntel Core i72.67 GHz32 KB L1 d-cache256 KB L2 cache8 MB L3 cacheGreat Reality #5:Computers do more than execute programs
  • They need to get data in and out
  • I/O system critical to program reliability and performance
  • They communicate with each other over networks
  • Many system-level issues arise in presence of network
  • Concurrent operations by autonomous processes
  • Coping with unreliable media
  • Cross platform compatibility
  • Complex performance issues
  • Role within CS CurriculumCS 4XXSys. ProgramCS 350OperatingSystemsEmbeddedSystemsRobotics.CS 432DatabasesCS 428NetworksCS 4XXCompilersDigitalComputationCS320ArchitectureConc.I/OProcessesMem. MgmtMachineCodeData Reps.Memory ModelExecution ModelMemory SystemArithmeticCS220Foundation of Computer SystemsUnderlying principles for hardware, software, and networkingCS 120Computer Sys ICourse Perspective
  • Most Systems Courses are Builder-Centric
  • Computer Architecture
  • Design pipelined processor in Verilog
  • Operating Systems
  • Implement large portions of operating system
  • Compilers
  • Write compiler for simple language
  • Networking
  • Implement and simulate network protocols
  • Course Perspective (Cont.)
  • This is Programmer-Centric
  • Purpose is to show that by knowing more about the underlying system, one can be more effective as a programmer
  • Enable you to
  • Write programs that are more reliable and efficient
  • Incorporate features that require hooks into OS
  • E.g., concurrency, signal handlers
  • Cover material in this course that you won’t see elsewhere
  • Not just a course for dedicated hackers
  • Lets bring out the hidden hacker in everyone!
  • Teaching staff
  • Instructor: Nael Abu-Ghazaleh
  • Best way to reach me is by email: nael@cs.binghamton.edu
  • Office: T-12 Engineering building
  • Office hours posted on class website
  • Primary TA: Christopher Rogers
  • crogers1@binghamton.edu
  • Office hours: TBA
  • CA: Matthew Williamson
  • mwilli20@binghamton.edu
  • Office hours: TBA
  • Textbooks
  • Randal E. Bryant and David R. O’Hallaron,
  • “Computer Systems: A Programmer’s Perspective, Second Edition” (CS:APP2e), Prentice Hall, 2011
  • http://csapp.cs.cmu.edu
  • This book really matters for the course!
  • How to solve labs
  • Practice problems typical of exam problems
  • Brian Kernighan and Dennis Ritchie,
  • “The C Programming Language, Second Edition”, Prentice Hall, 1988
  • Course Components
  • Lectures
  • Higher level concepts
  • Lab sessions
  • Applied concepts, important tools and skills for labs, clarification of lectures, exam coverage
  • Lab assignments (6)
  • The heart of the course
  • Average 2-3 weeks each
  • Provide in-depth understanding of an aspect of systems
  • Programming and measurement
  • Exams (Quizzes + Exams + final)
  • Test your understanding of concepts principles
  • Getting Help
  • Class Web page: http://www.cs.binghamton.edu/~nael/cs220
  • Complete schedule of lectures, exams, and assignments
  • Copies of lectures, assignments, exams, solutions
  • Clarifications to assignments
  • Blackboard
  • Class communication and probably for handing in projects; details will follow
  • Getting Help
  • Office hours: on class website
  • Labs and class
  • 1:1 Appointments
  • You can schedule 1:1 appointments with any of the teaching staff
  • Discussion through blackboard
  • Policies: Assignments (Labs) And Exams
  • Work groups
  • Unless specified, you must work alone on all assignments
  • Handins
  • Assignments due at 8pm on due date
  • Appealing grades
  • Within 7 days of completion of grading
  • Timeliness
  • Grace days
  • 4 grace days for the course
  • Limit of 2 grace days per lab used automatically
  • Covers scheduling crunch, out-of-town trips, illnesses, minor setbacks
  • Save them until late in the term!
  • Lateness penalties
  • Once grace day(s) used up, get penalized15% per day
  • No handins later than 4days after due date
  • Catastrophic events
  • Major illness, death in family, …
  • Let us know as early as possible
  • Advice
  • Once you start running late, it’s really hard to catch up
  • Cheating
  • What is cheating?
  • Sharing code: by copying, retyping, looking at, or supplying a file
  • Coaching: helping your friend to write a lab, line by line
  • Copying code from previous course or from elsewhere on WWW
  • Only allowed to use code we supply, or from CS:APP website
  • What is NOT cheating?
  • Explaining how to use systems or tools
  • Helping others with high-level design issues
  • Penalty for cheating:
  • Look at the Watson School Honesty Code
  • Detection of cheating:
  • We do check
  • Tools for doing this are much better than most cheaters think!
  • Other Rules
  • Laptops: permitted for class support
  • Taking notes; looking at slides; etc…
  • Electronic communications: forbidden
  • No email, instant messaging, cell phone calls, etc
  • Presence in lectures: highly recommended
  • Some labs sessions have required attendance
  • You risk missing quizzes
  • Policies: Grading
  • Exams (30%): Final (15%)
  • Labs (45%): weighted according to effort
  • Quizzes and class participation (10%)
  • Evil Instructor?
  • Must pass both Exams and Labs
  • What you score lower on will have higher weight in your grade
  • Not so evil
  • We will weight down your worst work in each category (exams and labs)
  • Final grades are relative to the rest of the class
  • Programs and Data
  • Topics
  • C
  • Bits operations, arithmetic, assembly language programs
  • Representation of C control and data structures
  • Includes aspects of architecture and compilers
  • Assignments
  • (C Lab): Fun with C pointers
  • (datalab): Manipulating bits
  • (bomblab): Defusing a binary bomb
  • (buflab): Implementing a code injection attack
  • The Memory Hierarchy
  • Topics
  • Memory technology, memory hierarchy, caches, disks, locality
  • Includes aspects of architecture and OS
  • Assignments
  • (cachelab): Building a cache simulator and optimizing for locality.
  • Learn how to exploit locality in your programs.
  • Performance
  • Topics
  • Co-optimization (control and data), measuring time on a computer
  • Includes aspects of architecture, compilers, and OS
  • Exceptional Control Flow
  • Topics
  • Hardware exceptions, processes, process control, Unix signals, nonlocal jumps
  • Includes aspects of compilers, OS, and architecture
  • Assignments
  • (tshlab): Writing your own Unix shell.
  • A first introduction to concurrency
  • Virtual Memory
  • Topics
  • Virtual memory, address translation, dynamic storage allocation
  • Includes aspects of architecture and OS
  • Assignments
  • (malloclab): Writing your own malloc package
  • Get a real feel for systems-level programming
  • I/O and Concurrency
  • Topics
  • High level and low-level I/O
  • concurrency, concurrent server design, threads
  • I/O multiplexing with select
  • Includes aspects of networking, OS, and architecture
  • Assignments
  • (proxylab): Writing your own Web proxy
  • Learn network programming and more about concurrency and synchronization.
  • Lab Rationale
  • Each lab has a well-defined goal such as solving a puzzle or winning a contest
  • Doing the lab should result in new skills and concepts
  • Try to use competition in a fun and healthy way
  • Set a reasonable threshold for full credit
  • Welcome and Enjoy!
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