09/27/2007ecs150 Fall 20071 Operating System ecs150 Fall 2007 : Operating System #1: OS...

transcript

09/27/2007 ecs150 Fall 2007 1

ecs150 Fall 2007:Operating SystemOperating System#1: OS Architecture, Kernel, & Process

Dr. S. Felix Wu

Computer Science Department

University of California, Davishttp://www.cs.ucdavis.edu/~wu/

sfelixwu@gmail.com

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VM/MVS, DOS, Win95/98/ME/2000/XP, Freebsd/Linux, MacOS-10, Mach, Minix, PalmOS, uCOS, TinyOS, …

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Applications……..

Hardware: CPU/Memory/HD/DVD/Wireless…

….where applications meet Hardware!!!

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““Information Router”Information Router”

One NIC a process’s user-level memory One file another file

– OS kernel layer– Hardware layer

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Applications……..

Hardware: CPU/Memory/HD/DVD/Wireless…

….where applications meet Hardware!!!

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This quarter….This quarter….

The internals of OS The basic design principles of OS The skills to modify or implement an OS.

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Operating SystemOperating System

An interesting balance between:– Theories and Practical Experiences/Experiments– Architectural Concept and Detailed Design– Formal Verification and Empirical Validation

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About the InstructorAbout the Instructor

S. Felix Wu – sfelixwu@gmail.com – Facebook group (under UCD network): ecs150

Office: 3057 Engineering II Phone: 530-754-7070 Office Hours:

– 1-2 p.m. on Tuesday and Friday– by appointment

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Why 3 email addresses?Why 3 email addresses?

– sfelixwu@gmail.com

– sfwu@ucdavis.edu

– sfelixwu@yahoo.com

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– sfwu@ucdavis.edu– My main email contact for everything all the time.

– sfelixwu@yahoo.com

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– sfelixwu@yahoo.com– Read only once in the past three months…

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read/response during the quarters, especially before the homework deadlines.

– sfelixwu@yahoo.com– Read only once in the past three months…

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Anti-SpamAnti-Spam

sfelixwu@gmail.com subject: [ecs150 f2007]…

[ecs150 2007]is the cyber social link between the instructor and the students in ecs150, fall 2007.

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Anti-SpamAnti-Spam

sfelixwu@gmail.com subject: [ecs150 f2007]… [ecs150 f2007] is the cyber social link

between the instructor and the students in ecs150, fall 2007.

Let’s see by the end of quarter whether this little secret will be known to the spammers…

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About the TAAbout the TA

TA Sean Whalen (shwhalen@gmail.com)– Office Hours: TBA– Discussion: Mon 4:10~5:00 (146 Olson)

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about Web siteabout Web site

http://www.cs.ucdavis.edu/~wu/ecs150/ Also the Facebook group all lectures, notes, announcements,

homework assignments, tools, papers will be there.

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TextbookTextbook

http://www.freebsd.org/

"The Design and Implementation of the FreeBSD Operating Systems" by Marshall Kirk McKusick and George V. Neville-Neil

Addison Wesley Professional, 2005, ISBN 0-201-70245-2.

Reading this book itself may be a major challenge.But, you really learn when you go through this process!

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PrerequisitesPrerequisites

Programming Languages: C and assembly (ecs50)

Date Structure (ecs110) and basic Computer Architecture (ecs154a/eec70).

ecs40 Please talk to me if you have any concern.

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SyllabusSyllabus

Process/Kernel (09) Memory Management (06) Midterm (11/01/2007, in class) IO & File Systems (10) Others (03) Final (12/13/2007, 8~10 a.m.)

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OS Principles/ConceptsOS Principles/Concepts

What is “kernel”?What is the difference between a process and a thread?What is the difference between user-level and kernel-level threads?What is the difference between a system call and a library function call?What are SJF, RR, Lottery, LRU, TLB, Second Chance?How to do Mutual Exclusion?What is the difference between deadlock prevention and avoidance?What are the differences among hardware interrupt, hardware trap, and software trap?

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Let’s examine OS concepts in a realistic context: “FreeBSD”

Then, we can re-think those concepts….– And, maybe you will realize later that some of

the concepts are either “misleading” or “irrelevant” in certain context.

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Principles vs. PracticePrinciples vs. Practice

Ideas and Theories first, then we will go over some FreeBSD code segments.

You will need to learn FreeBSD internals for programming assignments!!

The first few discussion sessions will be dedicated to FreeBSD internals.– Most of the discussion sessions are very important and

they will appear in the exams and homeworks.

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Course RequirementsCourse Requirements

48%: Programming Assignments– teamwork: 1~2 students (no more than 2!)– 4 Assignments (10%, 18%, 12%, 8%)– HW#1 is out.

16%: In-class open-book midterm 32%: open-book final 04%: Participation of Lectures and

Discussion sessions.– Deducted if missed more than TWO sessions.

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GradingGrading

I will give +/- grades. possible grading :

– A: >= 92 A-: >= 89 B+: >= 85– B: >= 82 B-: >= 79 C+: >= 75– C: >= 72 C-: >= 69 D+: >= 65– D: >= 62 D-: >= 59

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FreeBSDFreeBSD

You need to have access to a FreeBSD environment– I386, QEMU, VMware, VirtualPC, Parallel

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Standard Full Virtualization e.g.,

Unmodified OS (XP, Linux, Solaris, or, FreeBSD)

Unmodified Applications

Hardware

VirtualPCWindowXP

virtualizationvirtualization

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Virtual PC or VMware

Hardware

FreeBSDFreeBSD

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“Programmable” Full Virtualization

Hardware

Programmable VirtualizationProgrammable Virtualization

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The Structure of OSThe Structure of OS

The Kernel Processes and Threads The System Call Interface

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What is “kernel”?What is “kernel”?

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KernelKernel

The basic OS services Which services? What is it doing? Let’s check a couple examples

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….what are the basic services?

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FreeBSD Kernel: FreeBSD Kernel: ServicesServices

Timer/clock, descriptor, process Memory Management: paging/swapping I/O control and terminal File System Inter-process communication Networking

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Kernel of SVR2 of AT&T UnixKernel of SVR2 of AT&T Unix

hardware

System Call Interface

LibrariesUser programs

trapuser

File subsys

Buffer cache

Hardware Control

Character blockdevice drivers

ProcessControlSubsys.

Inter-ProcessCommunication

Scheduler

MemoryManagement

kernel

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Kernel & ProcessesKernel & Processes

The concept of “application process”

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Kernel and User SpaceKernel and User Space

Process FOOFOOMemoryspace for thisprocess

System call(or trap into the kernel)

program

System Call

conceptually

Kernel Resources(disk or IO devices)

Process FOOFOOin the Kernel

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ProcessesProcesses

> ps PID TTY TIME CMD 2910 pts/4 0:00 tcsh> ps -ef UID PID PPID C STIME TTY TIME CMD root 0 0 0 Sep 25 ? 0:01 sched root 1 0 0 Sep 25 ? 0:00 /etc/init - root 2 0 0 Sep 25 ? 0:00 pageout root 3 0 0 Sep 25 ? 0:01 fsflush root 223 1 0 Sep 25 ? 0:00 /usr/lib/utmpd root 179 1 0 Sep 25 ? 0:00 /usr/sbin/cron root 273 1 0 Sep 25 ? 0:00 /usr/lib/saf/sac -t 300 root 56 1 0 Sep 25 ? 0:00 /usr/lib/devfsadm/devfseventd root 58 1 0 Sep 25 ? 0:00 /usr/lib/devfsadm/devfsadmd root 106 1 0 Sep 25 ? 0:00 /usr/sbin/rpcbind root 197 1 0 Sep 25 ? 0:01 /usr/sbin/nscd root 108 1 0 Sep 25 ? 0:00 /usr/sbin/keyserv root 168 1 0 Sep 25 ? 0:00 /usr/sbin/syslogd root 118 1 0 Sep 25 ? 0:00 /usr/lib/netsvc/yp/ypbind root 159 1 0 Sep 25 ? 0:00 /usr/lib/autofs/automountd

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Memory StructureMemory StructureHigh

LowStack Growth

String Growth

Arguments

Return address

Prev. frame pointer

Local variables

Stack Pointer

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Memory StructureMemory StructureHigh

LowStack Growth

String Growth

Arguments

Return address

Prev. frame pointer

Local variables

Stack Pointer

bar( ){……}

foo( ){ …… call bar( ); ……}

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Procedure CallProcedure Call on the same on the same

User StackUser Stack

Per-processKernel Stack

User-stack

Initialized data Initialized data

text text

a.out header

a.out magic numberMemory

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System CallSystem Call on a different stack on a different stack

Per-processKernel Stack

User-stack

Initialized data Initialized data

text text

a.out header

a.out magic numberMemory

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System CallsSystem Calls

Not a “normal” procedure call

It is a software trap “into” the kernel– Hardware interrupt– Hardware trap– Software trap

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System EntrySystem Entry

Hardware interrupt– Asynchronous, might not relate to the context

of the executing process Hardware trap

– Related to the current executing process, e.g., divided by zero

Software-initiated trap– Instructions, int

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System Entry VectorSystem Entry Vector

fork()

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System Entry VectorSystem Entry Vector

fork()

TrapReserved forloadable system calls

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kldloadkldload

fork()

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OS ArchitectureOS Architecture

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ProcessProcess

Process – a program in execution A process includes:

– program counter – stack– data section

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Context SwitchingContext Switching

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Running

Blocked Ready

Running

Blocked Ready

Running

Blocked Ready

Running

Blocked Ready

Scheduling &Context Switching

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States of a ProcessStates of a Process

Running, Blocked, and Ready

Running

Waiting Ready

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256 different priorities64 scheduling classes

0~63 bottom-half kernel (interrupt)64~127 top-half kernel128~159 real-time user160~223 timeshare224~255 idle

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Kernel ProcessesKernel Processes

idle, swapper, vmdaemon, pagedaemon, pagezero, bufdaemon, syncer, ktrace, vnlru, random, g_event, g_up, g_down

/usr/src/sys/kern/kern_idle.c/usr/src/sys/kern/init_main.c/usr/src/sys/vm/vm_zeroidle.c/usr/src/sys/kern_ktrace.c/usr/src/sys/dev/random/randomsoft_dev.c

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Running

Waiting Ready

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4.4BSD Process Structure4.4BSD Process Structure(/usr/src/sys/sys/proc.h)(/usr/src/sys/sys/proc.h)

ProcessStructure

machine-dependentprocess information

process group

process credential

VM space

file descriptors

resource limits

statistics

signal actions

process control blockprocess kernel stack

session

user credential

region list

file entries

} user structure

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FreeBSD User StructureFreeBSD User Structure/*

* Per process structure containing data that isn’t needed in core when the

* process isn’t running (esp. when swapped out). This structure may or may not

* be at the same kernel address in all processes.

struct user {

struct pcb u_pcb;

struct sigacts u_sigacts; /* p_sigacts points here (use it!) */

struct pstats u_stats; /* p_stats points here (use it!) */

/* Remaining fields only for core dump and/or ptrace—

not valid at other times! */

struct kinfo_proc u_kproc; /* proc + eproc */

struce md_coredump u_md; /* machine dependent glop */

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5.x Kernel

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KSE:Kernel Scheduling Entity kernel-level thread

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What is a thread?What is a thread?

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Process and ThreadProcess and Thread(abstraction and abstraction)

An execution instance of a program. Threads and resources

– a thread is a control entity of the logical flow in the program.

– A sequential program needs only one single thread because it only need to be controlled by one entity.

– Can you distinguish a process and a thread?

User mode versus (trap into the) Kernel mode.

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A Program and ThreadsA Program and Threads

(shared)variables

If (j==0)

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ThreadsThreads

Heavy-weight Process versus Light-weight Thread

User-level versus Kernel-level

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a Process and a Threada Process and a Thread A tradition process contains one thread (i.e,

one flow of control) and the resources (user or kernel).

Resources

No obvious concurrency within a process

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Process and ThreadsProcess and Threads

A Process can contain more than one threads sharing the resources (user or kernel).

Resources

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ThreadsThreads

User-level Kernel-level

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ThreadsThreads

Blocking/Synchronous I/O– One thread blocks all others???– “Block one block all”

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mainmemory

I/O bridge

bus interface

register file

CPU chip

system bus memory bus

disk controller

graphicsadapter

USBcontroller

mousekeyboard monitor

I/O bus Expansion slots forother devices suchas network adapters.

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mainmemory

register file

CPU chip

disk controller

graphicsadapter

USBcontroller

I/O bus

bus interface

CPU initiates a disk read by writing a command, logical block number, and destination memory address to a port (address) associated with disk controller.

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mainmemory

register file

CPU chip

disk controller

graphicsadapter

USBcontroller

I/O bus

bus interface

Disk controller reads the sector and performs a direct memory access (DMA) transfer into main memory.

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mainmemory

register file

CPU chip

disk controller

graphicsadapter

USBcontroller

I/O bus

bus interface

When the DMA transfer completes, the disk controller notifies the CPU with an interrupt (i.e., asserts a special “interrupt” pin on the CPU)

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Asynchronous I/OAsynchronous I/O

How to deal with multiple I/O operations concurrently? For example: wait for a keyboard input, a mouse click and

input from a network connection.

Select system call

Poll system call (same idea, different implementation)

For more info see http://www.kegel.com/c10k.html

int select(int n, fd_set *readfds, fd_set *writefds, fd_set *exceptfds, struct timeval *timeout);

int poll(struct pollfd *ufds, unsigned int nfds, int timeout);

struct pollfd { int fd; /* file descriptor */ short events; /* requested events */ short revents; /* returned events */ };

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/usr/src/sys/kern/vfs_aio.c/usr/src/sys/kern/vfs_aio.c

POSIX P1003.4 Asynchronous I/O interface functions:– aio_cancel:cancel asynchronous read and/or write

requests – aio_error:retrieve Asynchronous I/O error status – aio_fsync:asynchronously force I/O completion, and sets

errno to ENOSYS – aio_read:begin asynchronous read – aio_return:retrieve return status of Asynchronous I/O

operation – aio_suspend:suspend until Asynchronous I/O Completes – aio_write:begin asynchronous write – lio_listio:issue list of I/O requests

Solaris, Linux 2.6, FreeBSD pp230~231

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Security Problem!!

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User-Level ThreadsUser-Level Threads

Now, you should get the basic idea about how to avoid “block one block all”….

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ThreadsThreads

User-level– Kernel is unaware of multiple threading within

the same process. (Conceptually, the kernel pretends one “kernel” thread per process.)

Kernel-level– Kernel is fully aware of multiple kernel threads

within the same process, and therefore, it will provide “related kernel services”.

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User and Kernel ThreadsUser and Kernel Threads One thread per process or multiple thread per

process

KernelTsUserLevelTs

Which approach is better???

KTS KTS

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User-Level ThreadsUser-Level Threads

A small OS in the user-space to manage the threads.

The kernel is totally unaware how many threads the process currently has.

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Why Multiple Threads??Why Multiple Threads??

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Responsiveness Resource Sharing Economy Utilization of MP Architectures

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fork()

fork()fork()Process A

GlobalVariables

Process B

GlobalVariables

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fork()Parent

GlobalVariables

execve()

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pthread_create()pthread_create()Process AThread 1

GlobalVariables

Process AThread 2

pthread_create()

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Creation Time DifferenceCreation Time Difference Because threads are by definition lightweight, they can be created

more quickly that “heavy” processes:

– Sun Ultra5, 320 Meg Ram, 1 CPU 94 forks()/second 1,737 threads/second (18x faster)

– Sun Sparc Ultra 1, 256 Meg Ram , 1 CPU 67 forks()/second 1,359 threads/second (20x faster)

– Sun Enterprise 420R, 5 Gig Ram, 4 CPUs 146 forks()/second 35,640 threads/second (244x faster)

– Linux 2.4 Kernel, .5 Gig Ram, 2 CPUs 1,811 forks()/second 227,611 threads/second (125x faster)

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User ThreadsUser Threads

Thread management done by user-level threads library

Examples

- POSIX Pthreads

- Mach C-threads

- Solaris threads

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Kernel ThreadsKernel Threads Supported by the Kernel Examples

- Windows 95/98/NT/2000

- Solaris

- Linux

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Solaris 2 ThreadsSolaris 2 Threads

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Linux ThreadsLinux Threads

Linux refers to them as tasks rather than threads.

Thread creation is done through clone() system call.

clone() allows a child task to share the address space of the parent task (process)

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Operating System(Linux Native Thread)

Programming Library(POSIX thread)

Programming Language(Java)

Application(Web Server)

System call: Clone

Thread class: run

Lib call:

pthread_create

Open new connection

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KT vs. UTKT vs. UT

pros and cons?

BTW, how about FreeBSD?

Threads

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UTS + KTSUTS + KTS Two independent schedulers:

processor processor processor

OS Kernel

Process Process Process

Scheduler

User Space

Scheduler Scheduler

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KTSKTS One single scheduler:

processor processor processor

OS Kernel

Process Process Process

Scheduler

User Space

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KT vs. UTKT vs. UT

Kernel Interface

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Solaris 2 ThreadsSolaris 2 Threads

mapping but NOT coordinating

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Questions to askQuestions to ask Why do we need “coordination”?

– kernel-support user-level threads What do we need in this “K/U

coordination”?– extended system call API

Is this only good for SMP?– How about single processor?– How about NPU? (e.g., IXP-2400)

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Kernel

Library

Notify I/O

events

Notify new

decision

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Kernel Space

User Space

Hardware

syscall

I/O request interrupt

I don’t know how many UT’s you have up there?

I can guess but I am not sure that is exactly what you want!

Is this a problem?

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Scheduler ActivationsScheduler Activations

Kernel Space

User Space

Hardware

upcall upcall

Kernel Space

User Space

Hardware

syscall

I/O request interrupt

CPU time wasted

CPU used

I don’t know how many UT’s you have up there?

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Scheduler ActivationsScheduler Activations First proposed by [Anderson et al. 91] Idea: cooperation between schedulers should take place in

both directions User scheduler uses system calls Kernel scheduler should use upcalls!

Upcalls– Notify the user-level of kernel scheduling events

Activations– A new structure to support upcalls (~kernel thread)– As many running activations as processors– Kernel controls activation creation and destruction

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Kernel

Library

KTS – virtual CPU’s

Notify I/O

events

UTS - threads

Notify new

decision

One Model (FreeBSD 5.x)

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I/O happens for ThreadI/O happens for Thread

(4)(3)(2)

User Program

User-LevelRuntime System

Operating System Kernel

Processors

AddProcessor

(A) (B)

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A’s Thread has blocked on an I/O requestA’s Thread has blocked on an I/O request

(3)(2)(1)

User Program

Processors

(A) (B) ( C )

A’s thread has blockedOperating System Kernel

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(4)(3)(2)

User Program

Processors

(A) (B) ( C )Operating System Kernel

(D) A’s thread and B’s Thread can continue

A’s Thread I/O completedA’s Thread I/O completed

“the upcall stack problem”

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A’s Thread resumes on Scheduler Activation D

(4)(3)(2)

User Program

Processors

( C )Operating System Kernel

(D) A’s thread and B’s Thread can continue

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Kernel

Library

Notify I/O

events

UTS - threads

Notify new

decision

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FreeBSD 5.xFreeBSD 5.x

Kernel Scheduling Entity (KSE)– a virtual CPU– When “anything” changes regarding the service

of this KSE to the process, this KSE is “unassigned” as the kernel doesn’t know what other threads might be there!!

– Upcall to the UTS (via KSE mailbox).– UTS uses both KSE mailbox and Thread

mailbox to handle/decide.

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#include <sys/types.h>#include <sys/kse.h>

int kse_create(struct kse_mailbox *mbx, int newsgroup);int kse_exit(void);int kse_release(struct timespec *timeout);int kse_wakeup(struct kse_mailbox *mbx);int kse_thr_interrupt(struct kse_thr_mailbox *tmbx);

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struct kse_mailbox {int km_version;struct kse_thr_mailbox *km_curthread; struct kse_thr_mailbox *km_completed;sigset_t km_sigscaught;unsigned int km_flags;kse_func_t *km_func; /* UTS function */stack_t km_stack; /* UTS context */void *km_udata; /* For use by the UTS */struct timespec km_timeofday; /* Time of day */int km_quantum;int km_spare[8];

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struct kse_thr_mailbox {ucontext_t tm_context; /* User and machine context */unsigned int tm_flags; /* Thread flags */struct kse_thr_mailbox *tm_next; /* Next thread in list */void *tm_udata; /* For use by the UTS */unsigned int tm_uticks;unsigned int tm_sticks;int tm_spare[8];

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upcallsupcalls

ksec_new ksec_preempt ksec_block ksec_unblock

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Kernel

Library

ksec_new

ksec_preempt

ksec_block

ksec_unblock

kse_createkse_exitkse_releasekse_wakeupkse_thr_interrupt

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KSE InternalKSE Internal

KSE KSEG KSEC

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Linux VPILinux VPI(Virtual Processor Interface)

Experimental/Research Prototype– Benson/Butner/Padden/Fedosov– Scheduler activation in Linux Kernel 2.4.18

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Kernel

Library

Notify I/O

events

UTS - threads

Notify new

decision

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Kernel ProcessesKernel Processes((table 3.1 page 50)table 3.1 page 50)

idle, swapper, vmdaemon, pagedaemon, pagezero, bufdaemon, syncer, ktrace, vnlru, random, g_event, g_up, g_down

“Kernel processes execute code that is complied into the kernel’s load image and operate with the kernel’s privileged execution code.”

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FreeBSD KernelFreeBSD Kernel

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FreeBSD KernelFreeBSD Kernel

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Kernel and User SpaceKernel and User Space

Process FOOFOOMemoryspace for thisprocess

System call(or trap into the kernel)

program

System Call

conceptually

Kernel Resources(disk or IO devices)

Process FOOFOOin the Kernel

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What is “micro-kernel”?What is “micro-kernel”?

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….what are the basic services?

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An Alternative: Micro-Kernel

Message Passing versus Optimized Procedure Calls

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System callsSystem calls

int 80h *.s (not in /usr/src/sys/kern/*) *.c (not in /usr/src/sys/kern/*) sysent/sysvec function pointer lkmnosys()

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/usr/src/sys/i386/i386/*.*

09/27/2007 ecs150 Fall 2007 145

Micro versus MonolithicMicro versus Monolithic

What is the real difference between these two models??

First Brainstorming!!

09/27/2007 ecs150 Fall 2007 146

Micro versus MonolithicMicro versus Monolithic

Is this really relevant? Advantages of Micro Kernels

– Modules (Architectural Cleanness), Adaptive, Small/Quick-to-Boot,…

We did learn some lessons– We have to consider the “users” &

“applications”, and make a new engineering design decision.

09/27/2007 ecs150 Fall 2007 147

FreeBSD Kernel: SizeFreeBSD Kernel: Size

689794 machine independent LOC 108346 machine dependent LOC 846525 device driver LOC

Comparing:– Windows 3.1 ~ 6M LOC– Windows 2000 ~ 30-50M LOC– Windows XP ~ 45M LOC– Netscape ~ 7M LOC

09/27/2007 ecs150 Fall 2007 148

OS DesignOS Design

Architectural Design– how to organize the user and kernel resources?

Module Control Design– how to design a control mechanism to protect the OS

resource integrity?

Interface Design– how to let user programs access the resources easier?

(e.g., system call interface, multi-threaded interface).

09/27/2007 ecs150 Fall 2007 149

What is “Process”? What is “System Call”? What is “Kernel”?

09/27/2007ecs150 Fall 20071 Operating System ecs150 Fall 2007 : Operating System #1: OS...

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