1. Operating Systems (OS) Threads, SMP, and Microkernel, Unix Kernel
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COMP5102/5122 Lecture 5
Operating Systems (OS)
Threads, SMP, and Microkernel, Unix Kernel

2. © De Montfort University, 2005
Lecture Outline
Threads,
SMP
Microkernels
Unix Kernel
IPC and deadlock
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Comp5102/ L5

3. © De Montfort University, 2005
Consider
A Process is a unit of:
Resource ownership
Dispatching (execution path, state)
What if we treat each independently?
Process resource ownership
Thread dispatch and execution unit
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4. © De Montfort University, 2005
Threads
Sometimes called a lightweight process
smaller execution unit than a process
Consists of:
program counter
register set
stack space
Threads share:
memory space
code section
OS resources(open files, signals, etc.)
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5. © De Montfort University, 2005
Multithreading
Most OS support multiple threads of execution within a single process
MS-DOS supports a single thread
UNIX supports multiple user processes but only supports one thread per process
Windows NT, Solaris, Linux, Mac, and OS/2 support multiple threads
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6. Threads Process 0 Process 1 regs regs regs mem code code memory
All threads in a process share the same memory space
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7. Single Threaded and Multithreaded Process Models
Control
Block
Thread
Control
Block
Thread
Control
Block
Process
Control
Block
User
Stack
Process
Control
Block
User
Stack
User
Stack
User
Stack
User
Address
Space
Kernel
Stack
User
Address
Space
Kernel
Stack
Kernel
Stack
Kernel
Stack
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8. © De Montfort University, 2005
Why use threads?
Parallelism
Uses fewer resources
Faster context switch
Threads can work together easier
Modularity
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Parallel Processing
The processing of program instructions by dividing them among multiple processors with the objective of running a program in less time.
Rather than speeding up hardware you could just add more processors to speed up the system.
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Comp5102/ L5

10. Flynn’s Classification
Based on the number of instruction streams and the number of data streams.
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11. Categories of Computer Systems
Single Instruction Single Data (SISD)
single processor executes a single instruction stream to operate on data stored in a single memory
Single Instruction Multiple Data (SIMD)
each instruction is executed on a different set of data by the different processors
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12. Categories of Computer …
Multiple Instruction Single Data (MISD)
a sequence of data is transmitted to a set of processors, each of which executes a different instruction sequence. Never implemented
Multiple Instruction Multiple Data (MIMD)
a set of processors simultaneously execute different instruction sequences on different data sets
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Comp5102/ L5

13. © De Montfort University, 2005
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14. Symmetric Multiprocessing
SMP is the processing of programs by multiple processors that share a common operating system and memory.
Kernel can execute on any processor
Typically each processor does self-scheduling from the pool of available process or threads
Timer interrupt
Ready queue
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Comp5102/ L5

15. Symmetric Multiprocessor Organization. . .
Processor
Cache
Cache
Cache
I/O adaptor
Main
Memory
I/O
Subsystem
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Comp5102/ L5

16. Multiprocessor Operating System
Design Considerations:
Simultaneous concurrent processes or threads
Scheduling
Synchronization
Memory Management
Reliability and Fault Tolerance
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17. © De Montfort University, 2005
Microkernel
Small operating system core
Contains only essential OS functions
Many services traditionally included in the operating system are now external subsystems
device drivers
file systems
virtual memory manager
windowing system and security services
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18. © De Montfort University, 2005
Microkernel OS U s e r P o c D e v i c r V i r t u a l M e m P r o c e s S v F i l e S y s t m
User Processes
File System
IPC
I/O & Device Mgmt
Virtual Memory
Process Management
Microkernel
Hardware
Hardware
Kernel Mode
User Mode
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19. © De Montfort University, 2005
Unix Kernel
Hardware is surrounded by the OS which is called the kernel
Comes with a number of services and interfaces
Shell
C compiler
strictly speaking, the kernel is Unix
monolithic in design; grown to a massive block
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Unix …
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Unix …
The Kernel can be split into two sections :-
Machine dependent
hardware control, incorporating low level i/o, device drivers, interrupt handlers, context switching and some memory management.
Machine independent
the rest
(see diagram in the book)
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22. © De Montfort University, 2005
Kernel Structures
The key structure is the process table
contains an entry for every process
contains information, accessible to the kernel.
The user area contains fields relating to the current process which can be swapped to disk
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23. Process table entries:-
Scheduling details:
priority, CPU usage, sleeping etc.
Identifiers:
process id, parent's id, user id.
Memory usage
Signals:
signals sent to the process but not yet dealt with.
Synchronisation
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24. © De Montfort University, 2005
The user area :-
machine registers in user state;
system call state - parameters and results;
file descriptor table -
current directory;
permission modes for creating files;
accounting information - user time, system time;
kernel stack.
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User processes - pre-emptive scheduling.
Unpriviledged.
Kernel - hardware independent - runs until completed or blocked.
Priviledged.
Kernel - hardware dependent - Never scheduled. Cannot block. Deals with interrupts. Runs on kernel stack, in kernel address space.
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26. © De Montfort University, 2005
Interrupt priorities
high priority
Machine errors
Clock
Disk
Network
Terminals
low priority
Software Interrupt
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Sleep And Wakeup
process executing in kernel may need to wait for some event.
executes the sleep routine.
state of process is changed to blocked
scheduler selects another process.
When the event occurs the interrupt routine executes:
wakeup routine executed by interrupt
process changed to ready state.
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28. © De Montfort University, 2005
Kernel sets the priority of the sleeping process according to the reason for sleeping.
e.g. we could have 3 processes contending for a locked buffer :-
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29. © De Montfort University, 2005
process A process B process C
buffer locked
sleeps
buffer locked, sleeps
buffer unlocked. A, B, C woken
- ready to run ready to run ready to run
Runs - locks
buffer
sleeps for
some reason
Runs - buffer
locked - sleeps Runs - buffer
locked - sleeps
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Comp5102/ L5

30. © De Montfort University, 2005
Summary
Symmetric multiprocessing is a method of organising a multiprocessing system such that any process (or thread) can run on any processor; this includes kernel codes and processes. An SMP architecture raises new operating systems design issues and provides greater performance than a uniprocessor system under similar conditions.
In recent years there has been much interest in the microkernel approach to operating system design. In its pure form, a microkernel operating system consists of a very small microkernel that runs in kernel mode and that contains only the most essential and critical operating system functions.
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Comp5102/ L5

31. Benefits of Microkernel Organization (Appendix A)
Uniform interface on request made by a process
all services are provided by means of message passing
Extensibility
allows the addition of new services
Flexibility
existing features can be subtracted
Portability
changes needed to port the system to a new processor is changed in the microkernel - not in the other services
Reliability
modular design
small microkernel can be rigorously tested
Distributed system support
message are sent without knowing what the target machine is
Object-oriented operating system
components are objects with clearly defined interfaces that can be interconnected to form software
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Comp5102/ L5

32. © De Montfort University, 2005
Assgnment:
Hand in in a folder:
One page explaining the shell programming and what is your work all about.
Don’t worry about bundling!
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Comp5102/ L5

33. © De Montfort University, 2005
Hand in a floppy disk, containing your programs.
Listing of your programs.
Make sure that you have commented the programs well and say in your introductory page how to run the programs.
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Comp5102/ L5

34. © De Montfort University, 2005
In your initialise file:
echo "0" > $HOME/trash/counter
Then in your del file to increment counter for each file deleted:
C=$HOME/trash/counter
CT=`cat $C`
CT=`expr $CT + 1`
echo "$CT" > $HOME/trash/counter
© De Montfort University, 2005
Comp5102/ L5