Threads, SMP, and Microkernels

1
Threads, SMP, and Microkernels

• Chapter 4

2
(No Transcript)
3
Multithreading

• Operating system supports 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, Solaris, Linux, Mach, and OS/2 support
  multiple threads

4
(No Transcript)
5
Process

• Resource ownership - process includes a virtual
  address space to hold the process image and
  access to I/O
• Scheduling/execution- follows an execution path
  that may be interleaved with other processes
• These two characteristics are treated
  independently by the operating system

6
Process

• Dispatching is referred to as a thread or
  lightweight process
• Resource of ownership is referred to as a process
  or task

7
Thread

• An execution state (running, ready, etc.)
• Saved thread context when not running
• Has an execution stack
• Some per-thread static storage for local
  variables
• Access to the memory and resources of its process
• all threads of a process share this

8
User-Level Threads
9
User-Level Threads

• All thread management is done by the application
• The kernel is not aware of the existence of
  threads
• I/O requests causes the whole process to be
  blocked.

10
Kernel-Level Threads
11
Kernel-Level Threads

• Windows is an example of this approach
• Kernel maintains context information for the
  process and the threads
• Scheduling is done on a thread basis
• I/O requests only cause the affect thread to be
  blocked.

12
VAX Running UNIX-Like Operating System
13
Combined Approaches
14
Combined Approaches

• Example is Solaris
• Thread creation done in the user space and kernel
  space
• Bulk of scheduling and synchronization of threads
  within application in both kernel and user space
• Communication between threads can be done in
  kernel or user space.

15
Benefits of Threads

• Takes less time to create a new thread than a
  process
• Less time to terminate a thread than a process
• Less time to switch between two threads within
  the same process
• Since threads within the same process share
  memory and files, they can communicate with each
  other without invoking the kernel

16
Uses of Threads in a Single-User Multiprocessing
System

• Foreground to background work Managing
  different processes with different levels of
  priority.
• Asynchronous processing Threads that can
  execute without care of what the other threads
  are doing.
• Speed of execution Faster to swap out threads
  than processes.

17
Threads - Review

• Suspending a process involves suspending all
  threads of the process since all threads share
  the same address space
• Termination of a process, terminates all threads
  within the process

18
Thread States

• States associated with a change in thread state
• Spawn
• Spawn another thread
• Block/Unblock
• Ready/Running
• Finish
• Deallocate register context and stacks

19
(No Transcript)
20
Processor Architectures
21
Categories of Computer Systems

• Single Instruction Single Data (SISD) stream
• Single processor executes a single instruction
  stream to operate on data stored in a single
  memory
• Single Instruction Multiple Data (SIMD) stream
• Each instruction is executed on a different set
  of data by the different processors

22
Categories of Computer Systems

• Multiple Instruction Single Data (MISD) stream
• 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

23
(No Transcript)
24
Symmetric Multiprocessing(MIMD)

• Kernel can execute on any processor
• Typically each processor does self-scheduling
  form the pool of available process or threads

25
(No Transcript)
26
Symmetric Multiprocessing(MIMD)

• What new issues might we have to deal with?
• Having to worry about proper sharing of Memory
• Two processes executing the same code either on
  purpose or by accident
• The Kernel can be running on multiple processors
  at the same time.

27
Multiprocessor Operating System Design
Considerations

• Simultaneous concurrent processes or threads
• Scheduling
• Synchronization
• Memory management
• Reliability and fault tolerance

28
Microkernels
29
Microkernels

• Small operating system core
• Contains only essential core operating systems
  functions
• Many services traditionally included in the
  operating system are now external subsystems
• Device drivers
• File systems
• Virtual memory manager
• Windowing system
• Security services

30
(No Transcript)
31
Benefits of a Microkernel Organization

• Uniform interface on request made by a process
• Dont distinguish between kernel-level and
  user-level services (Where are all the services?)
• All services are provided by means of message
  passing
• Extensibility
• Allows the addition of new services
• Flexibility
• New features added
• Existing features can be subtracted

32
Benefits of a Microkernel Organization

• 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

33
Benefits of Microkernel Organization

• 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

34
Microkernel Design

• Low-level memory management
• Mapping each virtual page to a physical page
  frame (Kernel)
• Memory protection and allocation (User-Level)

35
Microkernel

• Supporting External Paging and Virtual Memory
  Management
• Grant A User-Level process can grant/assign
  memory to another process.
• Map Placing one or more pages of memory in
  overlapping space.
• Flush The granter process can reclaim any
  memory.

36
Microkernel Design

• Interprocess communication
• Uses messages that contains a header and a body.
• I/O and interrupt management
• Interrupts recognized by the kernel, but handed
  off to a user-level process.

37
Closer Look at Windows and Solaris
38
Windows Processes

• Implemented as objects
• An executable process may contain one or more
  threads
• Both processes and thread objects have built-in
  synchronization capabilities
• Threads and Processes run in kernel mode

39
(No Transcript)
40
Solaris

• User-level and Kernel-level Threads
• Process includes the users address space, stack,
  and process control block
• Accessible by the Kernel Threads
• Lightweight processes (LWP)
• Shadow of the Process that allows the User-Level
  threads to function without making direct calls
  to the Kernel threads.

41
(No Transcript)
42
Windows 2000Thread States
43
(No Transcript)
44
End
45
Remote Procedure Call Using Single Thread
46
Remote Procedure Call Using Threads
47
Multithreading
48
Adobe PageMaker
49
(No Transcript)
50
(No Transcript)
51
(No Transcript)
52
Closer Look at Solaris
53
Solaris Lightweight Data Structure

• Identifier
• Priority
• Signal mask
• Saved values of user-level registers
• Kernel stack
• Resource usage and profiling data
• Pointer to the corresponding kernel thread
• Pointer to the process structure

54
(No Transcript)
55
Linux Task Data Structure

• State
• Scheduling information
• Identifiers
• Interprocess communication
• Links
• Times and timers
• File system
• Address space
• Processor-specific context

56
(No Transcript)
57
Linux States of a Process

• Running
• Interruptable
• Uninterruptable
• Stopped
• Zombie