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CS – Operating Systems, Slides of Operating Systems

Georgetown University (GU)Operating Systems

CS – Operating Systems. Instructor: David Mazières. CAs: Emma Dauterman, Peter Dunn, and Francis Yan. Stanford University.

Typology: Slides

2022/2023

Uploaded on 05/11/2023

lakshminath 🇺🇸

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223 documents

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CS140 – Operating Systems

Instructor: David Mazières

CAs: Emma Dauterman, Peter Dunn, and Francis Yan

Stanford University

1/ 35

Outline

1Administrivia

2Substance

2/ 35

Administrivia

•Class web page: http://cs140.scs.stanford.edu/

-All assignments, handouts, lecture notes on-line

•Textbook: Operating System Concepts, 8th Edition,

by Silberschatz, Galvin, and Gagne

-8th edition is available for ∼$10 used

-9th, 10th editions way more expensive, haven’t looked atthem

-Trying to ween class from textbookanyway—consider it optional

•Goal is to make lecture slides the primary reference

-Almost everything I talk about will be on slides

-PDF slides contain links to further reading about topics

-Please download slides from class web page

-Will try to post before lecture for taking notes

(but avoid calling out answers if you read them from slides)

3/ 35

Administrivia 2

•Google group 19wi-cs140 is main discussion forum

•Staff mailing list: cs140-staff@scs.stanford.edu

-Please use google group for questions other people might have

-Otherwise, please mail staff list, not individual instructors

•Key dates:

-Lectures: MW 3:00pm–4:20pm, Skilling

-Section: 6 Fridays, time/location TBD, starting this Friday

-Midterm exam: Wednesday, February 13, 3:00–4:20pm (in class)

-Final exam: Monday, March 18th, 3:30pm-6:30pm

•Possibly some joint sections with CS140e

•Exams open note, but not open book

-Bring notes, slides, any printed materials excepttextbook

-No electronic devices permitted

4/ 35

Lecture videos

•Lectures will be televised for SCPD students

-Can also watch if you miss a lecture, or to review

-But resist temptationto miss a bunch of lectures and watch them

all at once

•SCPD students welcome to attend lecture in person

•Other notes for SCPD students:

-Please attend exams in person if possible

-Feel free to use google group to find projectpartners

5/ 35

Course topics

•Threads & Processes

•Concurrency & Synchronization

•Scheduling

•Virtual Memory

•I/O

•Disks, File systems

•Protection & Security

•Virtual machines

•Note: Lectures will often takeUnix as an example

-Most current and future OSes heavily influenced by Unix

-Won’t talk much about Windows

6/ 35

Discover Slides of Operating Systems Georgetown University (GU)

Partial preview of the text

Download CS – Operating Systems and more Slides Operating Systems in PDF only on Docsity!

CS140 – Operating Systems

Instructor: David Mazières

CAs: Emma Dauterman, Peter Dunn, and Francis Yan

Stanford University

1 / 35

Outline

1 Administrivia

2 Substance

2 / 35

Administrivia

(^) Class web page: http://cs140.scs.stanford.edu/
- All assignments, handouts, lecture notes on-line
(^) Textbook: Operating System Concepts, 8th Edition,

by Silberschatz, Galvin, and Gagne

8th edition is available for ∼$10 used
9th, 10th editions way more expensive, haven’t looked at them
Trying to ween class from textbook anyway—consider it optional
(^) Goal is to make lecture slides the primary reference
Almost everything I talk about will be on slides
PDF slides contain links to further reading about topics
Please download slides from class web page
Will try to post before lecture for taking notes (but avoid calling out answers if you read them from slides)

3 / 35

Administrivia 2

(^) Google group 19wi-cs140 is main discussion forum
(^) Staff mailing list: [email protected]
- Please use google group for questions other people might have
- Otherwise, please mail staff list, not individual instructors
(^) Key dates:
- Lectures: MW 3:00pm–4:20pm, Skilling
- Section: 6 Fridays, time/location TBD, starting this Friday
- Midterm exam: Wednesday, February 13, 3:00–4:20pm (in class)
- Final exam: Monday, March 18th, 3:30pm-6:30pm
(^) Possibly some joint sections with CS140e
(^) Exams open note, but not open book
- Bring notes, slides, any printed materials except textbook
- No electronic devices permitted 4 / 35

Lecture videos

(^) Lectures will be televised for SCPD students
- Can also watch if you miss a lecture, or to review
- But resist temptation to miss a bunch of lectures and watch them all at once
(^) SCPD students welcome to attend lecture in person
(^) Other notes for SCPD students:
- Please attend exams in person if possible
- Feel free to use google group to find project partners

Course topics

(^) Threads & Processes
(^) Concurrency & Synchronization
(^) Scheduling
(^) Virtual Memory
(^) I/O
(^) Disks, File systems
(^) Protection & Security
(^) Virtual machines
(^) Note: Lectures will often take Unix as an example
- Most current and future OSes heavily influenced by Unix
- Won’t talk much about Windows

Course goals

(^) Introduce you to operating system concepts
- Hard to use a computer without interacting with OS
- Understanding the OS makes you a more effective programmer
(^) Cover important systems concepts in general
- Caching, concurrency, memory management, I/O, protection
(^) Teach you to deal with larger software systems
- Programming assignments much larger than many courses
- Warning: Many people will consider course very hard
- In past, majority of people report ≥15 hours/week
(^) Prepare you to take graduate OS classes (CS240, 240[a-z])

7 / 35

Programming Assignments

(^) Implement parts of Pintos operating system
- Built for x86 hardware, you will use hardware emulators
(^) One setup homework (lab 0) due this Friday
(^) Four implementation projects:
- Threads
- User processes
- Virtual memory
- File system
(^) Lab 1 distributed at end of this week
- Attend section this Friday for project 1 overview
(^) Implement projects in groups of up to 3 people
- Pick your partners today (lecture may end early for this)
- Please disclose if you are planning to take class pass/fail 8 / 35

Grading

(^) No incompletes
- Talk to instructor ASAP if you run into real problems
(^) Final grades posted March 26
(^) 50% of grade based on exams using this quantity:

max

midterm > 0? final : 0 , 21 ( midterm + final )

(^) 50% of grade from projects
- For each project, 50% of score based on passing test cases
- Remaining 50% based on design and style
(^) Most people’s projects pass most test cases
- Please, please, please turn in working code, or no credit here
(^) Means design and style matter a lot
- Large software systems not just about producing working code
- Need to produce code other people can understand
- That’s why we have group projects 9 / 35

Style

(^) Must turn in a design document along with code
- We supply you with templates for each project’s design doc
(^) CAs will manually inspect code for correctness
- E.g., must actually implement the design
- Must handle corner cases (e.g., handle malloc failure)
(^) Will deduct points for error-prone code w/o errors
- Don’t use global variables if automatic ones suffice
- Don’t use deceptive names for variables
(^) Code must be easy to read
- Indent code, keep lines and (when possible) functions short
- Use a uniform coding style (try to match existing code)
- Put comments on structure members, globals, functions
- Don’t leave in reams of commented-out garbage code 10 / 35

Assignment requirements

(^) Do not look at other people’s solutions to projects
- We reserve the right to run MOSS on present and past submissions
- Do not publish your own solutions in violation of the honor code
- That means using (public) github can get you in big trouble
(^) You may read but not copy other OSes
- E.g., Linux, OpenBSD/FreeBSD, etc.
(^) Cite any code that inspired your code
- As long as you cite what you used, it’s not cheating
- In worst case, we deduct points if it undermines the assignment
(^) Projects due Fridays (before section—TBD)
(^) Ask cs140-staff for extension if you run into trouble
- Be sure to tell us: How much have you done? How much is left? When can you finish by?

Outline

1 Administrivia

2 Substance

Multi-user OSes

Hardware

OS

emacs firefox

(^) Many OSes use protection to serve distrustful users/apps
(^) Idea: With N users, system not N times slower
- Users’ demands for CPU, memory, etc. are bursty
- Win by giving resources to users who actually need them
(^) What can go wrong?
- Users are gluttons, use too much CPU, etc. (need policies)
- Total memory usage greater than machine’s RAM (must virtualize)
- Super-linear slowdown with increasing demand (thrashing) (^) 17 / 35

Protection

(^) Mechanisms that isolate bad programs and people
(^) Pre-emption:
- Give application a resource, take it away if needed elsewhere
(^) Interposition/mediation:
- Place OS between application and “stuff”
- Track all pieces that application allowed to use (e.g., in table)
- On every access, look in table to check that access legal
(^) Privileged & unprivileged modes in CPUs:
- Applications unprivileged (unprivileged user mode)
- OS privileged (privileged supervisor/kernel mode)
- Protection operations can only be done in privileged mode

18 / 35

Typical OS structure

user^ P1^ P2^ P3^ P

kernel

driver driver driver

NIC console

disk

VM IPC

scheduler

file

system

sockets

TCP/IP

(^) Most software runs as user-level processes (P[1-4])
- process ≈ instance of a program
(^) OS kernel runs in privileged mode (orange)
- Creates/deletes processes
- Provides access to hardware 19 / 35

System calls

(^) Applications can invoke kernel through system calls
- Special instruction transfers control to kernel
- ...which dispatches to one of few hundred syscall handlers 20 / 35

System calls (continued)

(^) Goal: Do things application can’t do in unprivileged mode
- Like a library call, but into more privileged kernel code
(^) Kernel supplies well-defined system call interface
- Applications set up syscall arguments and trap to kernel
- Kernel performs operation and returns result
(^) Higher-level functions built on syscall interface
- printf, scanf, fgets, etc. all user-level code
(^) Example: POSIX/UNIX interface
- open, close, read, write, ...

System call example

(^) Standard library implemented in terms of syscalls
- printf – in libc, has same privileges as application
- calls write – in kernel, which can send bits out serial port

UNIX file system calls

(^) Applications “open” files (or devices) by name
- I/O happens through open files
(^) int open(char path, int flags, /int mode*/...);
- flags: O_RDONLY, O_WRONLY, O_RDWR
- O_CREAT: create the file if non-existent
- O_EXCL: (w. O_CREAT) create if file exists already
- O_TRUNC: Truncate the file
- O_APPEND: Start writing from end of file
- mode: final argument with O_CREAT
(^) Returns file descriptor—used for all I/O to file

23 / 35

Error returns

(^) What if open fails? Returns -1 (invalid fd)
(^) Most system calls return -1 on failure
- Specific kind of error in global int errno
(^) #include <sys/errno.h> for possible values
- 2 = ENOENT “No such file or directory”
- 13 = EACCES “Permission Denied”
(^) perror function prints human-readable message
- perror ("initfile"); → “initfile: No such file or directory”

24 / 35

Operations on file descriptors

(^) int read (int fd, void *buf, int nbytes);
- Returns number of bytes read
- Returns 0 bytes at end of file, or -1 on error
(^) int write (int fd, const void *buf, int nbytes);
- Returns number of bytes written, -1 on error
(^) off_t lseek (int fd, off_t pos, int whence);
- whence: 0 – start, 1 – current, 2 – end . (^) Returns previous file offset, or -1 on error
(^) int close (int fd);

25 / 35

File descriptor numbers

(^) File descriptors are inherited by processes
- When one process spawns another, same fds by default
(^) Descriptors 0, 1, and 2 have special meaning
- 0 – “standard input” (stdin in ANSI C)
- 1 – “standard output” (stdout, printf in ANSI C)
- 2 – “standard error” (stderr, perror in ANSI C)
- Normally all three attached to terminal
(^) Example: type.c
- Prints the contents of a file to stdout

26 / 35

type.c

void typefile (char *filename) { int fd, nread; char buf[1024];

fd = open (filename, O_RDONLY); if (fd == -1) { perror (filename); return; }

while ((nread = read (fd, buf, sizeof (buf))) > 0) write (1, buf, nread);

close (fd); }

(^) Can see system calls using strace utility (ktrace on BSD)

Protection example: CPU preemption

(^) Protection mechanism to prevent monopolizing CPU
(^) E.g., kernel programs timer to interrupt every 10 ms
- Must be in supervisor mode to write appropriate I/O registers
- User code cannot re-program interval timer
(^) Kernel sets interrupt to vector back to kernel
- Regains control whenever interval timer fires
- Gives CPU to another process if someone else needs it
- Note: must be in supervisor mode to set interrupt entry points
- No way for user code to hijack interrupt handler
(^) Result: Cannot monopolize CPU with infinite loop
- At worst get 1/N of CPU with N CPU-hungry processes

Resource allocation & performance

(^) Multitasking permits higher resource utilization
(^) Simple example:
- Process downloading large file mostly waits for network
- You play a game while downloading the file
- Higher CPU utilization than if just downloading
(^) Complexity arises with cost of switching
(^) Example: Say disk 1,000 times slower than memory
- 1 GB memory in machine
- 2 Processes want to run, each use 1 GB
- Can switch processes by swapping them out to disk
- Faster to run one at a time than keep context switching

Useful properties to exploit

(^) Skew
- 80% of time taken by 20% of code
- 10% of memory absorbs 90% of references
- Basis behind cache: place 10% in fast memory, 90% in slow, usually looks like one big fast memory
(^) Past predicts future (a.k.a. temporal locality)
- What’s the best cache entry to replace?
- If past ≈ future, then least-recently-used entry
(^) Note conflict between fairness & throughput
- Higher throughput (fewer cache misses, etc.) to keep running same process
- But fairness says should periodically preempt CPU and give it to next process

CS – Operating Systems, Slides of Operating Systems

Related documents

Partial preview of the text

Download CS – Operating Systems and more Slides Operating Systems in PDF only on Docsity!

CS140 – Operating Systems

Instructor: David Mazières

CAs: Emma Dauterman, Peter Dunn, and Francis Yan

Outline

1 Administrivia

2 Substance

Administrivia

by Silberschatz, Galvin, and Gagne

Administrivia 2

Lecture videos

Course topics

midterm > 0? final : 0 , 21 ( midterm + final )

1 Administrivia

2 Substance

Hardware

OS

emacs firefox

user^ P1^ P2^ P3^ P

kernel

NIC console

disk

VM IPC

scheduler

file

system

sockets

TCP/IP

type.c Mon Jan 07 10:46:30 2019 1

#include <fcntl.h>

#include <stdio.h>

#include <stdlib.h>

#include <unistd.h>

void

typefile (char *filename)

int fd, nread;

char buf[1024];

fd = open (filename, O_RDONLY);

if (fd == -1) {

perror (filename);

return;

while ((nread = read (fd, buf, sizeof (buf))) > 0)

write (1, buf, nread);

close (fd);

int

main (int argc, char **argv)

int argno;

for (argno = 1; argno < argc; argno++)

typefile (argv[argno]);

exit (0);