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ecs150 Spring 2006:Operating SystemOperating System#1: OS Architecture, Kernel, & Process
Dr. S. Felix Wu
Computer Science Department
University of California, Davishttp://www.cs.ucdavis.edu/~wu/
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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…
OS
….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…
OS
….where applications meet Hardware!!!
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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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“Programmable” Full Virtualization
Unmodified OS (XP, Linux, Solaris, or, FreeBSD)
Unmodified Applications
Hardware
AP
I
DLVM
Programmable VirtualizationProgrammable Virtualization
DLVM
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Virtual PC or VMware
Unmodified OS (XP, Linux, Solaris, or, FreeBSD)
Unmodified Applications
Hardware
AP
I
FreeBSDFreeBSD
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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 – [email protected], x4-7070
Office: 3057 Engineering II Office Hours:
– 1-2 p.m. on Tuesday and Friday– by appointment
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About the TAAbout the TA
TA Valerie Szudziejka ([email protected])
– Office Hours: TBA– Discussion:
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about Web siteabout Web site
http://www.cs.ucdavis.edu/~wu/ecs150/ 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 is 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 IO & File Systems (10) Others (03) final
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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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OSOS
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: 1~3 students– 3 Programming Assignments (12%, 18%, 18%)– HW#1 is out (check the website).
16%: In-class open-book midterm 32%: open-book final 04%: Participation of Lectures and Discussion
sessions.– Deducted if missed more than three sessions.
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GradingGrading
I will give +/- grades. possible grading (not finalized):
– A: >= 93 A-: >= 90 B+: >= 87– B: >= 84 B-: >= 81 C+: >= 78– C: >= 75 C-: >= 72 D : > 60
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FreeBSDFreeBSD
Your team need to have access to a FreeBSD environment– I386, VMware, VirtualPC
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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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OS
….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( ); ……}
foo
bar
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Procedure CallProcedure Call on the same on the same
User StackUser Stack
Per-processKernel Stack
User-stack
Heap
Initialized data Initialized data
text text
a.out header
a.out magic numberMemory
Disk
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System CallSystem Call on a different stack on a different stack
Per-processKernel Stack
User-stack
Heap
Initialized data Initialized data
text text
a.out header
a.out magic numberMemory
Disk
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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()
::
Trap
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System Entry VectorSystem Entry Vector
fork()
::
TrapReserved forloadable system calls
XYZ()
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kldloadkldload
fork()
::
Trap
XYZ()
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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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1
0
0
1
0
1
::.
256 different priorities64 scheduling classes
RR
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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1
0
0
1
0
1
::.
256 different priorities64 scheduling classes
RR
0~63 bottom-half kernel (interrupt)64~127 top-half kernel128~159 real-time user160~223 timeshare224~255 idle
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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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1
0
0
1
0
1
::.
256 different priorities64 scheduling classes
RR
0~63 bottom-half kernel (interrupt)64~127 top-half kernel128~159 real-time user160~223 timeshare224~255 idle
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
J=0;
If (j==0)
J=100
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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
ALU
register file
CPU chip
system bus memory bus
disk controller
graphicsadapter
USBcontroller
mousekeyboard monitor
disk
I/O bus Expansion slots forother devices suchas network adapters.
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mainmemory
ALU
register file
CPU chip
disk controller
graphicsadapter
USBcontroller
mousekeyboard monitor
disk
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
ALU
register file
CPU chip
disk controller
graphicsadapter
USBcontroller
mousekeyboard monitor
disk
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
ALU
register file
CPU chip
disk controller
graphicsadapter
USBcontroller
mousekeyboard monitor
disk
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???
UTS
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
Code
Stack
Process B
GlobalVariables
Code
Stack
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fork()Parent
GlobalVariables
Code
Stack
Child
GlobalVariables
Code
Stack
Child
GlobalVariables
Code
Stack
execve()
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pthread_create()pthread_create()Process AThread 1
GlobalVariables
Code
Stack
Process AThread 2
Stack
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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O p era tin g S ys tem(L in u x N ative Th read )
P rog ram m in g L ib ra ry(P O S IX th read )
P rog ram m in g L an g u ag e(Java)
A p p lica tion(W eb S erver)
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
UTS
KTS
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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
KTS
Notify I/O
events
UTS
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
SA SA
SA SA
One Model (FreeBSD 5.x)
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I/O happens for ThreadI/O happens for Thread
(4)(3)(2)
(1)
User Program
User-LevelRuntime System
Operating System Kernel
Processors
AddProcessor
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
(4)
(3)(2)(1)
User Program
User-LevelRuntime System
Processors
B
(A) (B) ( C )
A’s thread has blockedOperating System Kernel
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(4)(3)(2)
(1)
User Program
User-LevelRuntime System
Processors
(A) (B) ( C )Operating System Kernel
(1)
(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
User-LevelRuntime System
Processors
( C )Operating System Kernel
(1)
(D) A’s thread and B’s Thread can continue
(1)
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Kernel
Library
KTS – virtual CPU’s
Notify I/O
events
UTS - threads
Notify new
decision
SA SA
SA SA
One Model (FreeBSD 5.x)
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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
KTS
UTS
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
KTS – virtual CPU’s
Notify I/O
events
UTS - threads
Notify new
decision
SA SA
SA SA
One Model (FreeBSD 5.x)
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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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OS
….what are the basic services?
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An Alternative: Micro-Kernel
Message Passing versus Optimized Procedure Calls
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Micro versus MonolithicMicro versus Monolithic
What is the real difference between these two models??
First Brainstorming!!
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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.
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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
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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).
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What is “Process”? What is “System Call”? What is “Kernel”?
