Threads smp and microkernels
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Threads, SMP, and Microkernels. Chapter 4. Process. Resource ownership: process includes a virtual address space to hold the process image (fig 3.16) Scheduling/execution: follows an execution path that may be interleaved with other processes

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Threads smp and microkernels

Threads, SMP, and Microkernels

Chapter 4



  • Resource ownership: process includes a virtual address space to hold the process image (fig 3.16)

  • Scheduling/execution: follows an execution path that may be interleaved with other processes

  • These two characteristics can be treated independently by the operating system



  • Unit of dispatching is referred to as a thread or lightweight process

  • Unit of resource ownership is referred to as a process or task



  • 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



  • Have a virtual address space which holds the process image

  • Protected access to processors, other processes, files, and I/O resources



  • 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

Benefits of threads

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

Uses of threads in a single user multiprocessing system

Uses of Threads in a Single-User Multiprocessing System

  • Foreground to background work

  • Asynchronous processing

  • Speed of execution

  • Modular program structure



  • 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

Thread states

Thread States

  • States associated with a change in thread state

    • Spawn

      • Spawn another thread

    • Block

    • Unblock

    • Finish

      • Deallocate register context and stacks

Remote procedure call using single thread

Remote Procedure Call Using Single Thread

Remote procedure call using threads

Remote Procedure Call Using Threads



Adobe pagemaker

Adobe PageMaker

User level threads

User-Level Threads

  • All thread management is done by the application

  • The kernel is not aware of the existence of threads

User level threads1

User-Level Threads

Advantages of user level threads

Advantages of User-Level Threads

  • Thread-switching does not require kernel mode privileges and switching

  • Thread scheduling can be tailored to application

  • ULTs can run on any OS. They can be implemented with a thread library that runs within the app.

Disadvantages of ults

Disadvantages of ULTs

  • If blocking system call (eg IO call), whole process blocked

    • can use ‘jacketing’ – call other process to check state of resource

  • Cannot use multiprocessing since OS sees all threads as a single process.

Kernel level threads

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

Kernel level threads1

Kernel-Level Threads

Vax running unix like operating system

VAX Running UNIX-Like Operating System

Combined approaches

Combined Approaches

  • Example is Solaris

  • Thread creation done in the user space

  • Bulk of scheduling and synchronization of threads within application

Combined approaches1

Combined Approaches

Relationship between threads and processes

Relationship Between Threads and Processes

1:M and M:N approaches are experimental.

Symmetric multiprocessing smp

Symmetric Multiprocessing (SMP)

Symmetric multiprocessing

Symmetric Multiprocessing

  • Tradition: Single sequence of instructions

    • von Neumann machine concept

  • Real machines do instruction pipelining, DMA and other parallel operations

    • Pipeline explanation and movie

    • Hyperthreading

  • With cheaper HW can extend this to multiple processors

Categories of computer systems

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.

    • ‘Normal’ computing

  • Single Instruction Multiple Data (SIMD) stream

    • Each instruction is executed on a different set of data by the different processors.

    • Eg DSP or vector processing

Categories of computer systems1

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

Symmetric multiprocessing1

Symmetric Multiprocessing

  • Kernel can execute on any processor

  • Typically each processor does self-scheduling from the pool of available process or threads

Multiprocessor operating system design considerations

Multiprocessor Operating System Design Considerations

  • Simultaneous concurrent processes or threads

    • Re-entrant kernel code, deadlock, etc.

  • Scheduling (see ch 10 for more detail)

  • Synchronization

    • Mutual exclusion, event ordering, locks etc (ch 5)

  • Memory management

    • Coordination in paging systems when multiple processors accessing pages (ch 7)

  • Reliability and fault tolerance

    • Graceful degradation on processor failure

Distributed processing

Distributed Processing

  • Another alternative is distributed processing

  • Each node has its own CPU, memory and communication channel

    • Slower communications, more independence

  • EG. Cluster computing, Beowulf etc.

    • See Ch 14, 15





  • Small operating system core (how small?)

  • Concept: 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

Benefits of a microkernel organization

Benefits of a Microkernel Organization

  • Uniform interface on request made by a process

    • Don’t distinguish between kernel-level and user-level 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

Benefits of a microkernel organization1

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

      • Exhaustive testing vs. module testing

Benefits of microkernel organization

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

Microkernel design

Microkernel Design

  • Low-level memory management

    • Mapping each virtual page to a physical page frame

Microkernel design1

Microkernel Design

  • Interprocess communication

  • I/O and interrupt management

Ms windows processes

MS-Windows Processes

  • Implemented as objects

  • An executable process may contain one or more threads

  • Both processes and thread objects have built-in synchronization capabilities

Windows process object

Windows Process Object

Windows thread object

Windows Thread Object

Ms windows thread states

MS-Windows Thread States

  • Ready

  • Standby

  • Running

  • Waiting

  • Transition

  • Terminated



  • Process includes the user’s address space, stack, and process control block

  • User-level threads

  • Lightweight processes (LWP)

  • Kernel threads

Solaris lightweight data structure

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

Linux task data structure

Linux Task Data Structure

  • State

  • Scheduling information

  • Identifiers

  • Interprocess communication

  • Links

  • Times and timers

  • File system

  • Address space

  • Processor-specific context

Linux states of a process

Linux States of a Process

  • Running

  • Interruptible

  • Uninterruptible

  • Stopped

  • Zombie

Linux threads

Linux Threads

  • Traditionally no threads

    • ULTs with pthread library

  • Modern Linux supports KLT

  • Process = thread (cloning)

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