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April 1, 2021 TCSS422: Operating Systems [Spring 2021] School of Engineering and Technology, University of Washington - Tacoma
Operating Systems –
Three Easy Pieces & Processes
Wes J. Lloyd
School of Engineering and Technology
University of Washington - Tacoma
TCSS 422: OPERATING SYSTEMS
Questions from 3/
C Review Survey
Student Background Survey
Virtual Machine Survey
Chapter 2: Operating Systems – Three Easy Pieces
Concepts of virtualization/abstraction
Three Easy Pieces: CPU, Memory, I/O
Concurrency
Operating system design goals
Chapter 4: Processes
Process states, context switches
Kernel data structures for processes and threads
April 1, 2021 TCSS422: Operating Systems [Spring 2021] School of Engineering and Technology, University of Washington - Tacoma L2. OBJECTIVES – 4/
Daily Feedback Quiz in Canvas – Available After Each Class
Extra credit available for completing surveys ON TI ME
Tuesday surveys: due by ~ Wed @ 11:59p
Thursday surveys: due ~ Mon @ 11:59p
April 1, 2021 TCSS422: Computer Operating Systems [Spring 2021] School of Engineering and Technology, University of Washington - Tacoma L2. ONLINE DAILY FEEDBACK SURVEY April 1, 2021 TCSS422: Computer Operating Systems [Spring 2021] School of Engineering and Technology, University of Washington - Tacoma L2.
Please classify your perspective on material covered in today’s
class (63 respondents):
1-mostly review, 5-equal new/review, 10-mostly new
Average – 5 .59 (no previous trend yet)
Please rate the pace of today’s class:
1-slow, 5-just right, 10-fast
Average – 5 .33 (no previous trend yet)
April 1, 2021 TCSS422: Computer Operating Systems [Spring 2021] School of Engineering and Technology, University of Washington - Tacoma L2. MATERIAL / PACE April 1, 2021 TCSS422: Operating Systems [Spring 2021] School of Engineering and Technology, University of Washington - Tacoma L2. FEEDBACK
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Questions from 3/
C Review Survey
Student Background Survey
Virtual Machine Survey
Chapter 2: Operating Systems – Three Easy Pieces
Concepts of virtualization/abstraction
Three Easy Pieces: CPU, Memory, I/O
Concurrency
Operating system design goals
Chapter 4: Processes
Process states, context switches
Kernel data structures for processes and threads
April 1, 2021 TCSS422: Operating Systems [Spring 2021] School of Engineering and Technology, University of Washington - Tacoma L2. OBJECTIVES – 4/ C REVIEW SURVEY April 1, 2021 TCSS422: Operating Systems [Spring 2021] School of Engineering and Technology, University of Washington - Tacoma L2.
Questions from 3/
C Review Survey
Student Background Survey
Virtual Machine Survey
Chapter 2: Operating Systems – Three Easy Pieces
Concepts of virtualization/abstraction
Three Easy Pieces: CPU, Memory, I/O
Concurrency
Operating system design goals
Chapter 4: Processes
Process states, context switches
Kernel data structures for processes and threads
April 1, 2021 TCSS422: Operating Systems [Spring 2021] School of Engineering and Technology, University of Washington - Tacoma L2. OBJECTIVES – 4/
Please complete the Student Background Survey
https://forms.gle/yr6Dc9x9rX516U6t
April 1, 2021 TCSS422: Operating Systems [Spring 2021] School of Engineering and Technology, University of Washington - Tacoma L2. STUDENT BACKGROUND SURVEY
Questions from 3/
C Review Survey
Student Background Survey
Virtual Machine Survey
Chapter 2: Operating Systems – Three Easy Pieces
Concepts of virtualization/abstraction
Three Easy Pieces: CPU, Memory, I/O
Concurrency
Operating system design goals
Chapter 4: Processes
Process states, context switches
Kernel data structures for processes and threads
April 1, 2021 TCSS422: Operating Systems [Spring 2021] School of Engineering and Technology, University of Washington - Tacoma L2. OBJECTIVES – 4/
Please complete the Virtual Machine Survey to request
a “School of Engineering and Technology” remote
hosted Ubuntu VM
https://forms.gle/BR2G1wr9RDBVB9AK
April 1, 2021 TCSS422: Operating Systems [Spring 2021] School of Engineering and Technology, University of Washington - Tacoma L2. VIRTUAL MACHINE SURVEY
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Simple Looping C Program
April 1, 2021 TCSS422: Operating Systems [Spring 2021] School of Engineering and Technology, University of Washington - Tacoma L2. VIRTUALIZING THE CPU - 2 12 #include#include <stdio.h><stdlib.h> 34 #include#include <sys/time.h><assert.h> 56 #include "common.h" 78 intmain(int argc, char *argv[]) 910 { if (argc != 2 ) { 1112 fprintf(stderr,exit( 1 ); "usage: cpu \n"); 1314 }char *str = argv[ 1 ]; 1516 while ( 1 ) (^) Spin({ 1 ); // Repeatedly checks the time and 17 returnsprintf("%s\n", str);^ once^ it^ has run for a^ second 1819 }return 0 ; 20 }
Runs forever, must Ctrl-C to halt…
April 1, 2021 TCSS422: Operating Systems [Spring 2021] School of Engineering and Technology, University of Washington - Tacoma L2. VIRTUALIZING THE CPU - 3 prompt> prompt> gcc./cpu "A" -o cpu cpu.c -Wall A A A ˆC prompt> April 1, 2021 TCSS422: Operating Systems [Spring 2021] School of Engineering and Technology, University of Washington - Tacoma L2. VIRTUALIZATION THE CPU - 4 prompt> [1] 7353 ./cpu A & ; ./cpu B & ; ./cpu C & ; ./cpu D & [2] 7354 [3] 7355 [4] 7356 A B D C A B D C A C B D ... Even though we have only one processor, all four instances of our program seem to be running at the same time!
& - run a job in the background
fg – brings a job to the foreground
bg – sends a job to the background
CTRL-Z to suspend a job
CTRL-C to kill a job
“jobs” command – lists running jobs
“jobs –p” command – lists running jobs by process ID
top –d .2 top utility shows active running jobs like
the Windows task manager
top –H –d .2 display all processes & threads
top –H –p display all threads of a process
htop alternative to top, shows CPU core graphs
April 1, 2021 TCSS422: Operating Systems [Spring 2021] School of Engineering and Technology, University of Washington - Tacoma L2. MANAGING PROCESSES FROM THE CLI
Questions from 3/
C Review Survey
Student Background Survey
Virtual Machine Survey
Chapter 2: Operating Systems – Three Easy Pieces
Concepts of virtualization/abstraction
Three Easy Pieces: CPU, Memory, I/O
Concurrency
Operating system design goals
Chapter 4: Processes
Process states, context switches
Kernel data structures for processes and threads
April 1, 2021 TCSS422: Operating Systems [Spring 2021] School of Engineering and Technology, University of Washington - Tacoma L2. OBJECTIVES – 4/
Computer memory is treated as a large array of bytes
Programs store all data in this large array
Read memory (load)
Specify an address to read data from
Write memory (store)
Specify data to write to an address
April 1, 2021 TCSS422: Operating Systems [Spring 2021] School of Engineering and Technology, University of Washington - Tacoma L2. VIRTUALIZING MEMORY
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Program to read/write memory:
April 1, 2021 TCSS422: Operating Systems [Spring 2021] School of Engineering and Technology, University of Washington - Tacoma L2. VIRTUALIZING MEMORY - 2 12 #include#include <unistd.h><stdio.h> 34 #include#include <stdlib.h>"common.h" (^56) int 78 main({ int argc, char *argv[]) 9 int *p = malloc(sizeof(int)); memory // a1: allocate some 1011 assert(pprintf("(%d) != NULLaddress); of p: %08x\n", 12 getpid(), (unsigned) address of the p); // a2: memmoryprint out the 1314 p =while 0 ;( (^1) )// a3: { put zero into the first slot of the memory 1516 Spin(p = *p 1 ); + 1 ; (^1718) } printf("(%d) p: %d\n", getpid(), *p); // a (^1920) } return 0 ;
Output of mem.c
int value stored at 00200000
program increments int value
April 1, 2021 TCSS422: Operating Systems [Spring 2021] School of Engineering and Technology, University of Washington - Tacoma L2. VIRTUALIZING MEMORY - 3 prompt> (2134) memory address./mem of p: 00200000 (2134) (2134) p:p: (^12) (2134) (2134) p:p: (^34) (2134) ˆC p: 5
Multiple instances of mem.c
(int*)p receives the same memory location 00200000
Why does modifying (int*)p in program #1 (PID=24113), not
interfere with (int*)p in program #2 (PID=24114)?
The OS has “virtualized” memory, and provides a “virtual” address
April 1, 2021 TCSS422: Operating Systems [Spring 2021] School of Engineering and Technology, University of Washington - Tacoma L2. VIRTUALIZING MEMORY - 4 prompt> [1] 24113 ./mem &; ./mem & [2] 24114 (24113) memory address of p: 00200000 (24114) (24113) memoryp: 1 address of p: 00200000 (24114) (24114) p: 1p: 2 (24113) (24113) p: 2p: 3 (24114) ... p: 3
Key take-aways:
Each process (program) has its own vir tual address space
The OS maps virtual address spaces onto
physical memory
A memory reference from one process can not affect the
address space of others.
Isolation
Physical memory, a shared resource, is managed by the OS
April 1, 2021 TCSS422: Operating Systems [Spring 2021] School of Engineering and Technology, University of Washington - Tacoma L2. VIRTUAL MEMORY
Questions from 3/
C Review Survey
Student Background Survey
Virtual Machine Survey
Chapter 2: Operating Systems – Three Easy Pieces
Concepts of virtualization/abstraction
Three Easy Pieces: CPU, Memory, I/O
Concurrency
Operating system design goals
Chapter 4: Processes
Process states, context switches
Kernel data structures for processes and threads
April 1, 2021 TCSS422: Operating Systems [Spring 2021] School of Engineering and Technology, University of Washington - Tacoma L2. OBJECTIVES – 4/
DRAM: Dynamic Random Access Memory: DIMMs/SIMMs
Stores data while power is present
When power is lost, data is lost (volatile)
Operating System helps “persist” data more permanently
I/O device(s): hard disk drive (HDD), solid state drive (SSD)
File system(s): “catalog” data for storage and retrieval
April 1, 2021 TCSS422: Operating Systems [Spring 2021] School of Engineering and Technology, University of Washington - Tacoma L2. PERSISTENCE
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thread.c
Listing continues …
April 1, 2021 TCSS422: Operating Systems [Spring 2021] School of Engineering and Technology, University of Washington - Tacoma L2. CONCURRENCY - 2 12 #include#include <stdio.h><stdlib.h> 34 #include "common.h" 56 volatile intint loops; counter = 0 ; (^78) void *worker(void *arg) { 910 intfor i;(i = 0 ; i < loops; i++) { (^1112) } counter++; (^1314) } return NULL; 15 ...
Not the same as Java volatile: Provides a compiler hint than an object may change value
unexpectedly (in this case by a separate thread) so aggressive
optimization must be avoided.
Program creates two threads
Check documentation: “man pthread_create”
worker() method counts from 0 to argv[1] (loop)
April 1, 2021 TCSS422: Operating Systems [Spring 2021] School of Engineering and Technology, University of Washington - Tacoma L2. CONCURRENCY - 3 1617 intmain(int argc, char *argv[]) 1819 { if (argc != 2 ) { 2021 fprintf(stderr,exit( 1 ); "usage: threads \n"); 2223 }loops = atoi(argv[ 1 ]); 2425 pthread_t p1, p2;printf("Initial value : %d\n", counter); (^2627) Pthread_create(&p1, NULL, worker, NULL); 2829 Pthread_create(&p2,Pthread_join(p1, NULL NULL);, worker, NULL); 3031 Pthread_join(p2,printf("Final value : %d\n", NULL); counter); (^3233) } return 0 ; April 1, 2021 TCSS422: Operating Systems [Spring 2021] School of Engineering and Technology, University of Washington - Tacoma L2.
Linux
“man”
page
example
April 1, 2021 TCSS422: Operating Systems [Spring 2021] School of Engineering and Technology, University of Washington - Tacoma L2. CONCURRENCY - 4
Command line parameter argv[1] provides loop length
Defines number of times the shared counter is incremented
Loops: 1000
Loops 100000
prompt> gcc prompt> ./thread 1000 -o thread thread.c -Wall -pthread Initial value : Final value : 2000 0 prompt> ./thread 100000 Initial value : 0 Final value prompt> ./thread 100000 : 143012 // huh?? Initial value : Final value : 137298 (^0) // what the??
When loop value is large why do we not achieve 200000?
C code is translated to (3) assembly code operations
1. Load counter variable into register
2. Increment it
3. Store the register value back in memory
These instructions happen concurrently and VERY FAST
(P1 || P2) write incremented register values back to memory,
While (P1 || P2) read same memory
Memory access here is unsynchronized (no n-atomic)
Some of the increments are lost
April 1, 2021 TCSS422: Operating Systems [Spring 2021] School of Engineering and Technology, University of Washington - Tacoma L2. CONCURRENCY - 5 April 1, 2021 TCSS422: Operating Systems [Spring 2021] School of Engineering and Technology, University of Washington - Tacoma L2.
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To perform parallel work, a single process may:
A. Launch multiple threads to execute code in parallel while
sharing global data in memory
B. Launch multiple processes to execute code in parallel
without sharing global data in memory
C. Both A and B
D. None of the above
April 1, 2021 TCSS422: Operating Systems [Spring 2021] School of Engineering and Technology, University of Washington - Tacoma L2. PARALLEL PROGRAMMING
Questions from 3/
C Review Survey
Student Background Survey
Virtual Machine Survey
Chapter 2: Operating Systems – Three Easy Pieces
Concepts of virtualization/abstraction
Three Easy Pieces: CPU, Memory, I/O
Concurrency
Operating system design goals
Chapter 4: Processes
Process states, context switches
Kernel data structures for processes and threads
April 1, 2021 TCSS422: Operating Systems [Spring 2021] School of Engineering and Technology, University of Washington - Tacoma L2. OBJECTIVES – 4/
ABSTRACTING THE HARDWARE
Makes programming code easier to write
Automate sharing resources – save programmer burden
PROVIDE HIGH PERFORMANCE
Minimize overhead from OS abstraction
(Virtualization of CPU, RAM, I/O)
Share resources fairly
Attempt to tradeoff performance vs. fairness consider
priority
PROVIDE ISOLATION
User programs can’t interfere with each other’s virtual
machines, the underlying OS, or the sharing of resources
April 1, 2021 TCSS422: Operating Systems [Spring 2021] School of Engineering and Technology, University of Washington - Tacoma L2. SUMMARY: OPERATING SYSTEM DESIGN GOALS
RELIABILIT Y
OS must not crash, 24/7 Up-time
Poor user programs must not bring down the system:
Blue Screen
Other Issues:
Energy-efficiency
Security (of data)
Cloud: Virtual Machines
April 1, 2021 TCSS422: Operating Systems [Spring 2021] School of Engineering and Technology, University of Washington - Tacoma L2. SUMMARY: OPERATING SYSTEM DESIGN GOALS - 2 WE WILL RETURN AT 5:00PM April 1, 2021 TCSS422: Operating Systems [Spring 2021] School of Engineering and Technology, University of Washington - Tacoma L2.
Questions from 3/
C Review Survey
Student Background Survey
Virtual Machine Survey
Chapter 2: Operating Systems – Three Easy Pieces
Concepts of virtualization/abstraction
Three Easy Pieces: CPU, Memory, I/O
Concurrency
Operating system design goals
Chapter 4: Processes
Process states, context switches
Kernel data structures for processes and threads
April 1, 2021 TCSS422: Operating Systems [Spring 2021] School of Engineering and Technology, University of Washington - Tacoma L2. OBJECTIVES – 4/
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April 1, 2021 TCSS422: Operating Systems [Spring 2021] School of Engineering and Technology, University of Washington - Tacoma L2. static data^ code heap stack Process Memory static data^ code heap Program
Loading:
Reads program from
disk into the address
space of process
CPU
Questions from 3/
C Review Survey
Student Background Survey
Virtual Machine Survey
Chapter 2: Operating Systems – Three Easy Pieces
Concepts of virtualization/abstraction
Three Easy Pieces: CPU, Memory, I/O
Concurrency
Operating system design goals
Chapter 4: Processes
Process states, context switches
Kernel data structures for processes and threads
April 1, 2021 TCSS422: Operating Systems [Spring 2021] School of Engineering and Technology, University of Washington - Tacoma L2. OBJECTIVES – 4/
RUNNING
Currently executing instructions
READY
Process is ready to run, but has been preempted
CPU is presently allocated for other tasks
BLOCKED
Process is not ready to run. It is waiting for another event
to complete:
Process has already been initialized and run for awhile
Is now waiting on I/O from disk(s) or other devices
April 1, 2021 TCSS422: Operating Systems [Spring 2021] School of Engineering and Technology, University of Washington - Tacoma L2. PROCESS STATES April 1, 2021 TCSS422: Operating Systems [Spring 2021] School of Engineering and Technology, University of Washington - Tacoma L2. PROCESS STATE TRANSITIONS Running Ready Blocked Descheduled Scheduled I/O: initiate I/O: done
Can inspect the number of CONTEXT SWITCHES made by a
process
Let’s run mem.c (from chapter 2)
cat /proc/{process-id}/status
proc “status” is a virtual file generated by Linux
Provides a report with process related meta-data
What appears to happen to the number of context s witches
the lo nger a process runs? (mem.c)
April 2, 2020 TCSS422: Operating Systems [Spring 2020] School of Engineering and Technology, University of Washington - Tacoma L2. OBSERVING PROCESS META-DATA
How long does a context s witch take?
10,000 to 50,000 ns (.01 to .05 ms)
2,000 context switches is near 100ms
April 2, 2020 TCSS422: Operating Systems [Spring 2020] School of Engineering and Technology, University of Washington - Tacoma L2. CONTEXT SWITCH
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April 1, 2021 TCSS422: Operating Systems [Spring 2021] School of Engineering and Technology, University of Washington - Tacoma L2.
When a process is in this state, it is advantageous for the
Operating System to perform a CONTEXT SWITCH to
perform other work:
(a) RUNNING
(b) READY
(c) BLOCKED
(d) All of the above
(e) None of the above
April 1, 2021 TCSS422: Operating Systems [Spring 2021] School of Engineering and Technology, University of Washington - Tacoma L2. QUESTION: WHEN TO CONTEXT SWITCH
Questions from 3/
C Review Survey
Student Background Survey
Virtual Machine Survey
Chapter 2: Operating Systems – Three Easy Pieces
Concepts of virtualization/abstraction
Three Easy Pieces: CPU, Memory, I/O
Concurrency
Operating system design goals
Chapter 4: Processes
Process states, context switches
Kernel data structures for processes and threads
April 1, 2021 TCSS422: Operating Systems [Spring 2021] School of Engineering and Technology, University of Washington - Tacoma L2. OBJECTIVES – 4/
OS provides data structures to track process information
Process list
Process Data
State of process: Ready, Blocked, Running
Register context
PCB (Process Control Block)
A C-structure that contains information about each
process
April 1, 2021 TCSS422: Operating Systems [Spring 2021] School of Engineering and Technology, University of Washington - Tacoma L2. PROCESS DATA STRUCTURES
xv6: pedagogical implementation of Linux
Simplified structures shown in book
April 1, 2021 TCSS422: Operating Systems [Spring 2021] School of Engineering and Technology, University of Washington - Tacoma L2. XV6 KERNEL DATA STRUCTURES // // theto stopregisters and subsequently restart xv6 will save and restore a process struct int context { eip; // Index pointer register int int esp;ebx; //// Stack pointerCalled the base register register int int ecx;edx; //// Called the counterCalled the data register register int int esi;edi; //// Source indexDestination index register register };^ int^ ebp;^ //^ Stack base pointer^ register // enum the proc_state different { UNUSED,states a processEMBRYO, SLEEPING, can be in RUNNABLE, RUNNING, ZOMBIE }; April 1, 2021 TCSS422: Operating Systems [Spring 2021] School of Engineering and Technology, University of Washington - Tacoma L2. XV6 KERNEL DATA STRUCTURES - 2 // the information xv6 tracks about each process // including its struct proc { register context and state char uint *mem;sz; // Start of// Size of processprocess memory memory char *kstack; // Bottom of // for this processkernel stack enum int pid;proc_state state; // Process// Process stateID struct void *chan; proc *parent; // Parent process// If non-zero, sleeping on chan int struct killed; file (^) *ofile[NOFILE];// If // Open files non-zero, have been killed struct inode *cwd; // Current directory struct struct context context;trapframe *tf; // Switch here to run// Trap frame for the process };^ // current^ interrupt
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OFFICE HOURS HAVE STEPPED OUT WILL RETURN SHORTLY
