CSE 5343/7343 Fall 2006 - PowerPoint PPT Presentation

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CSE 5343/7343 Fall 2006

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Title: CSE 5343/7343 Fall 2006


1
CSE 5343/7343Fall 2006
  • Case Studies
  • UNIX

2
UNIX Case Study Outline
  • History
  • Design Philosophy
  • Process Management
  • Processes
  • PCB/Process Table/U Area
  • Process States
  • Process Scheduling/Priorities
  • IPC
  • Memory Management
  • File Systems

3
History (2,3)
  • 1965 Bell and GE joined project MAC at MIT to
    develop Multics. Goal multicomputing and data
    sharing for a large group of users.
  • Ken Thompson (Bell) developed a game called
    Space Travel and found an unused PDP-7.
  • 1969
  • Thompson and Ken Ritchie implemented an earlier
    designed file system on PDP-7.
  • This grew into UNIX.
  • File system design and idea of command
    interpreter (shell) as a user process came from
    Multics
  • Fork idea came from Berkeleys GENIE OS.

4
History (contd)
  • 1971 UNIX used in first real project text
    processing for BELL labs patent department.
  • 1971 UNIX required 16K bytes for system, 8K
    bytes for user programs, 512K bytes of disk, and
    limit of 64K disk bytes per file.
  • Thompson set out to write a new Fortran compiler
    but developed a new programming language B. B
    was based on BCPL (a tool for compiler writing
    and systems programming). B was interpretive.
    He later improved on B and called it C.
  • 1973 UNIX rewrittten in C (unheard of at the
    time). ATT offered UNIX free to universities.
  • 1974 Ritchie and Thompson paper describing UNIX
    in CACM.

5
History (contd)
  • 1977 - Bell combined several versions into UNIX
    System II and marketed. History (contd)
  • 1978 After distribution of Ver7 in 1978, the
    Unix Support Group (USG) at ATT took over
    responsibilities from the research for
    distribution within ATT.
  • 1982 First external distribution from USG
    System III.
  • UC Berkeley developed their version of UNIX
    (Berkeley software Distributions).
  • BSD introduced vi in 2BSD, demand-pages virtual
    memory in 3BSD, TCP/IP networking protocol in
    4.2BSD.
  • Less than 3 of BSD written in assembly.
  • 1991 Finnish student Linus Torvalds wrote Linux
    for 80386, 32 bit processor

6
Design Philosophy (2,3)
  • Smplicity
  • C
  • Time-sharing
  • Simple user interface (modular and may be
    replaced)
  • Device independence (treat files and devices in
    same manner)
  • Aimed for programming environment
  • Flexibility

7
Design (contd)
  • Programs such as shell and vi interact with
    kernel using well defined system call procedures.
  • Cc built on top of c preprocessor, two-pass
    compiler.

8
UNIX
  • Process
  • Management

9
Processes
  • Process is program in execution
  • Consists of machine instructions (text), data,
    and stack regions.
  • Separate stack for user and kernel mode.
  • PID (Process ID)
  • Processes are either user processes, daemon
    processes, or kernel processes.
  • Daemons are not associated with user, but do
    system wide functions. Init may create daemons
    that exist throughout the life of the system or
    as needed.

10
Solaris Threads (3)
  • Kernel and user level threads
  • Only kernel level threads are scheduled
  • Implements Pthread API
  • LWP between kernel and user level threads
  • Each LWP associated with a kernel thread.
  • User processes have at least one LWP.
  • User threads may be bound or unbound to a LWP.
  • May have kernel thread without LWP.
  • Pool of LWPs for a process

11
Solaris Threads (contd)
  • User level thread
  • Thread ID
  • Registers
  • Stack pointer/stack
  • Priority
  • Process
  • Process ID
  • Memory map
  • Open files
  • Priority
  • LWPs
  • Kernel thread
  • Copy of kernel registers
  • Pointer to LWP
  • Priority
  • Scheduling information
  • Stack
  • LWP
  • Registers
  • Memory
  • Accounting information

12
PCB (1,2,4)
  • Process Table
  • State
  • UID for owner
  • Memory status (swapped or in memory)
  • Parent PID
  • Child PID
  • Event descriptor if suspended
  • Entry in kernel process table that points to
    process region table. These in turn point to
    entries in the region table and to the regions
    for that process. This allows independent
    processes to share regions.

13
U (User) Area (2)
  • Information needed when process is executing.
  • Process table slot
  • Information about current system call
  • File descriptors for open files
  • Current directory
  • Current root
  • Login terminal
  • Kernel has direct access to U area of currently
    executing process.

14
Process States (1,2)
  • No context switch is needed to go from state 2 to
    state 1.
  • States 3 and 7 are really the same.
  • I/O request puts process to sleep.
  • Zombie state Child has finished execution, but
    parent wants to get information about it from the
    PCB.

15
Process Hierarchy (1)
  • Initial boot process (0) forks a child (process
    1) and process 0 becomes the swapper. Process 1
    is init process and is ancestor of all other
    processes.
  • Parent/Child/Sibling relationship indicated by
    pointers in process table.
  • Execve usually called to replace memory portion
    of new process.
  • Exit process termination
  • Wait Parent waits for child to exit. Reclaims
    process resources.
  • Process group ID (GID) in process table
  • Execute ps -alx

16
Process Scheduling(2,3,5)
  • Typical time slice values
  • 4.3BSD 1/10 second
  • System V 50-100 times per second
  • Round robin multilevel feedback queue
  • At end of context switch, kernel executes
    algorithm to schedule a process.
  • Highest priority process which is ready is
    scheduled. On tie, picks the one which has
    waited the longest.

17
Process Scheduling (contd)
  • Higher number Lower Priority
  • User and kernel priorities user below kernel.
  • User mode priority is function of recent CPU
    usage. Lower priority if recently used CPU.
  • Priority assigned based on process group

18
Process Scheduling (contd)
  • Kernel to user mode change to user mode and
    calculate based on kernel resources just used.
  • Clock Handler adjusts all user mode process
    priorities at 1 second (System V) intervals and
    causes kernel to reschedule.
  • Decay function adjusts recent CPU usage values at
    this time decay(CPU) CPU/2
  • Priority is recalculated at these 1 second
    intervals plus when a process is in the preempted
    but ready to run state priority CPU/2 base
    level priority
  • Base level priority is the threshold between user
    and kernel mode.
  • Processes move up in queue but can not change to
    kernel mode.

19
IPC (2,3)
  • Pipes Only used from descendents of process
    that created the pipe.
  • Named Pipes- Used by unrelated processes. Has a
    directory entry and is accessed as a file.
  • Signals
  • Inform process of occurrence of asynchronous
    events.
  • Handling of signal by user process. Address of
    this routine is located in uarea next to signal
    number.
  • Socket
  • Introduced by 4.2BSD
  • Transient object Exists only as long as some
    process holds a descriptor referring to it.
  • Created by socket system call

20
IPC (contd)
  • Messages (System V)
  • On sending a message, a new entry is added to the
    associated linked list and the message is copied
    form the uarea. Message headers arranged in FIFO
    order.
  • Kernel awakens processes waiting for a message
    from this queue.
  • On receiving a message, process indicates what
    should be done if no message on the queue.

21
IPC (contd)
  • Shared Memory (System V)
  • System call creates a new region of shared memory
    or returns a current one.
  • Reading and writing is done as normal no system
    calls.
  • Shared memory remains in tact even if no
    processes include it in their virtual address
    space.

22
IPC (contd)
  • Semaphores (System V)
  • System calls create and use semaphore.
  • Semaphore array where each entry is the count
    value.
  • If process is put to sleep, it sleeps at an
    interruptable priority and wakes up on receipt of
    a signal.
  • Handled similar to messages with id being the
    entry in the semaphore table.

23
UNIX
  • Memory
  • Management

24
Memory Management (1,2)
  • Depends on platform and version
  • Early versions
  • Swapping
  • Transferred entire processes
  • 3BSD First demand-paged VM

25
Swapping (2)
  • Kernel swaps out a process if more memory space
    needed
  • Fork system call must allocate space for child
  • Size of process increases
  • Kernel wants to free memory for processes
    previously swapped out
  • Picking target process
  • Zombie are not swapped (they take up no memory)
  • Sleeping swapped out before ready to run
  • Depends on Priority and time in memory
  • If no sleeping process then ready to run based on
    nice value and time in memory

26
Swapping (contd)
  • Nice Value used to change to scheduling priority
  • Process 0 Swapper
  • Highest scheduling priority
  • Problem thrashing

27
Demand Paging System V 2
  • Approximate working set
  • Additional Page Table entries Valid
  • Reference
  • Modify
  • Copy on Write New copy must be created if
    updated
  • Age Time in working set
  • Disk Block Descriptor
  • Location on disk (VM)
  • Demand fill Immediately overwrite contents
    during exec
  • Demand zero Clear contents

28
Address Translation (4.3BSD Vax)1
  • Each region of address space mapped to a separate
    pag etable
  • Separate User and system area page tables
  • Two-level mapping, first level page tables reside
    in virtual memory
  • Page is 512 bytes
  • Virtual address
  • First two bits indicate regions
  • 10 system
  • 01 P0 - stack (user stack, kernel stack)
  • 00 P1 - Heap, data, text
  • User translation requires two levels of
    translation

29
Page Replacements Clock (4.3) 1
30
Clock Algorithm Example
Process 1
PT
0 1 2 3 4
Frame
Update
Disk
Valid
Process 2
PT
31
Start State
0 1 2 3 4
32
Create Process 1 / Load into VM
Process 1
PT

0 0 0 0
0 1 2 3 4
A B C D
Frame
Update
Disk
Valid
33
Load 1st Two Pages of P1 into Memory
Process 1
PT

0 0
1 3
1 1 0 0
A B
0 1 2 3 4
A B C D
Frame Table
1 0 1 0 1
1 1
Frame
Update
Disk
Valid
PID
Ref
Free
34
P1 Begins Executing using Pages 01
Process 1
PT

0 0
1 3
1 1 0 0
A B
0 1 2 3 4
A B C D
Frame Table
1 0 1 0 1
1 1
1 1
Frame
Update
Disk
Valid
PID
Ref
Free
35
Create Process 2 / Load into VM
Process 1
PT

0 0
1 3
1 1 0 0
A B
0 1 2 3 4
A B C D
Frame Table
1 0 1 0 1
1 1
1 1
Frame
Update
Disk
Valid
Process 2
PT
PID
Ref
Free
D E F

0 0 0
36
Load 1st Two Pages of P2 into Memory
Process 1
PT

0 0
1 3
1 1 0 0
E A D B
0 1 2 3 4
A B C D
Frame Table
0 0 0 0 1
2 1 2 1
0 1 0 1
Frame
Update
Disk
Valid
Process 2
PT
PID
Ref
Free
D E F

0 0
1 1 0
2 0
37
P2 Begins Executing using Pages 01 Update Page
1
Process 1
PT

0 0
1 3
1 1 0 0
E A D B
0 1 2 3 4
A B C D
Frame Table
0 0 0 0 1
2 1 2 1
1 1 1 1
Frame
Update
Disk
Valid
Process 2
PT
PID
Ref
Free
D E F

0 1
1 1 0
2 0
38
P2 Page Fault for Page 2 P1 Executes During
Paging I/O
Process 1
PT

0 0
1 3
1 1 0 0
E A D B F
0 1 2 3 4
A B C D
Frame Table
0 0 0 0 0
2 1 2 1 2
1 1 1 1 0
Frame
Update
Disk
Valid
Process 2
PT
PID
Ref
Free
D E F

0 1 0
1 1 1
2 0 4
39
I/O Completion Interrupt P2 Begins Execution -
Updates Page 2
Process 1
PT

0 0
1 3
1 1 0 0
E A D B F
0 1 2 3 4
A B C D
Frame Table
0 0 0 0 0
2 1 2 1 2
1 1 1 1 1
Frame
Update
Disk
Valid
Process 2
PT
PID
Ref
Free
D E F

0 1 1
1 1 1
2 0 4
40
Timer Interrupt P1 Begins Execution Page
Fault for Page 2 No Free Frames Initiate
Clock Algorithm for Page Replacement
Process 1
E A D B F
0 1 2 3 4
41
Replace Frame 0 Must swap out to disk as updated
Process 1
PT

0 0 0
1 3 0
1 1 1 0
C A D B F
0 1 2 3 4
A B C D
Frame Table
0 0 0 0 0
1 1 2 1 2
0 0 0 0 0
Frame
Update
Disk
Valid
Process 2
PT
PID
Ref
Free
D E F

0 1 2
1 0 1
2 0 4
42
References
  • Samuel J. Leffler, Marshall Kirk McKusick,
    Michael J. Karels, and John S. Quarterman, The
    Design and Implementation of the 4.3 BSD UNIX
    Operating System, Addison-Wesley, 1989.
  • Maurice J. Bach, The Design of the UNIX Operating
    System, Prentice Hall, 1990.
  • Abraham Silberschatz, Peter Baer Galvin, and Greg
    Gagne, Operating System Concepts Sixth Edition,
    John Wiley Sons, 2002.
  • Milan Milenkovic, Operating Systems Concepts and
    Design Second Edition, McGraw Hill, 1992.
  • Andrew S. Tanenbaum, Modern Operating Systems,
    Prentice Hall, 1992.
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