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Threads, SMP, and Microkernels. Chapter 4. Process: Some Info. Motivation for threads! Two fundamental aspects of a “process”: Resource ownership Scheduling or execution Resource ownership - process includes a virtual address space to hold the process image

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Threads, SMP, and Microkernels

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Threads smp and microkernels

Threads, SMP, and Microkernels

Chapter 4

Process some info

Process: Some Info.

  • Motivation for threads!

  • Two fundamental aspects of a “process”:

    • Resource ownership

    • Scheduling or execution

  • Resource ownership - process includes a virtual address space to hold the process image

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

  • These two characteristics are treated independently by the operating system



  • Dispatching is referred to as a thread or lightweight process

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

  • So far, we have considered processes that had just one thread:

    • A “process” or a “process with one thread” are kind of similar!



  • An attempt to define 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

What exactly is a process now

What exactly is a Process now?

  • Have a virtual address space which holds the process image

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

What exactly is a thread now

What exactly is a Thread now?

  • 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:

    • In GUI-based applications, one thread can make display and the other can process input

  • Asynchronous processing:

    • Daemons or services in OSes

  • Speed of execution:

    • Make even better use of processor, especially in multiprocessor systems

  • Modular program structure

Threads what happens to state models

Threads: What happens to state models?

  • 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



Top command

TOP Command

Pstree command

PSTREE Command

Proc directory on linux

/proc directory on Linux

Details of process 2114

Details of Process 2114

Adobe pagemaker

Adobe PageMaker

Categories of thread implementation

Categories of Thread Implementation

  • User-level threads

  • Kernel-level threads

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

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

Flynn s taxonomy

Flynn’s Taxonomy

  • There is no authoritative classification of parallel computers!

  • Flynn’s taxonomy is one such classification based on number of instruction and data stream processed by a parallel computer:

    • Single Instruction Single Data (SISD)

    • Multiple Instruction Single Data (MISD)

    • Single Instruction Multiple Data (SIMD)

    • Multiple Instruction Multiple Data (MIMD)

      • Almost all modern computers fall in this category

Flynn s taxonomy1

Flynn’s Taxonomy

  • Extensions to Flynn’s taxonomy:

    • Single Program Multiple Data (SPMD)—a programming model

  • This classification is largely outdated!

Symmetric multi processors smp

Symmetric Multi-Processors (SMP)

  • A SMP is a parallel processing system with a shared-everything approach:

    • The term signifies that each processor shares the main memory and possibly the cache

  • Typically a SMP can have 2 to 256 processors

  • Examples include AMD Athlon, AMD Opteron 200 and 2000 series, Intel XEON etc

Shared memory

Shared Memory

  • All processors have access to shared memory:

    • Notion of “Global Address Space”

Multiprocessor operating system design considerations

Multiprocessor Operating System Design Considerations

  • Simultaneous concurrent processes or threads:

    • Executing same kernel code should not result in erroneous behavior

  • Scheduling:

    • Opportunities exist to execute multiple threads of the same process

  • Synchronization

  • Memory management

  • Reliability and fault tolerance



  • 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

Benefits of a microkernel organization

Benefits of a Microkernel Organization

  • Uniform interface on request made by a process

  • Extensibility

  • Flexibility

  • Portability

  • Reliability

  • Distributed System Support

  • Object-oriented Operating System

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

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